Engineering chemistry-I

ENGINEERING CHEMISTRY-I ANNAPOORANA ENGINEERING COLLEGE V.S.SaravanamanIEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 2 ANNAPOORANA ENGINEERING COLLEGE PERIYASEERAGAPADI, NH-47, SANKARI MAIN ROAD, SALEM ENGINEERING CHEMISTRY-I by Department of ChemistryEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 3 ENGINEERING CHEMISTRY-I UNIT I WATER TECHNOLOGY 9 Characteristics – alkalinity – types of alkalinity and determination – hardness –types and estimation by EDTA method (problems); Domestic water treatment –disinfection methods (Chlorination, ozonation. UV treatment) – Boiler feed water– requirements – disadvantages of using hard water in boilers – Internal conditioning (phosphate, calgon and carbonate conditioning methods) – external conditioning – demineralization process – desalination and reverse osmosis. UNIT II POLYMERS AND COMPOSITES 9 Polymers-definition – polymerization – types – addition and condensation polymerization – free radical polymerization mechanism – Plastics, classification – preparation, properties and uses of PVC, Teflon, polycarbonate, polyurethane nylon-6,6, PET-Rubber -vulcanization of rubber, synthetic rubbers – buty1 rubber, SBR, Composites – definition, types polymer matrix composites – FRP only. UNIT III SURFACE CHEMISTRY 9 Adsorption – types – adsorption of gases on solids – adsorption isotherms – Frendlich and Langmuir isotherms – adsorption of solutes from solution – role of adsorbents in catalysis, ionexchhang adsorption and pollution abatement. UNITIV NON-CONVENTIONAL ENERGY SOURCES AND STORAGE DEVICES 9 Nuclear energy – fission and fusion reactions and light water nuclear reactor for power generation (block diagram only) – breeder reactor – solar energy conversion – solar cells – wind energy – fuel cells – hydrogen – oxygen fuel cell –batteries – alkaline batteries – lead–acid, nickel– cadmium and lithium batteries. UNIT V ENGINEERING MATERIALS 9 Refractories – classification – acidic, basic and neutral refractories – properties (refractoriness, refractoriness under load, dimensional stability, porosity, thermal spalling) – manufacture of Alumina, Magnesite and Zirconia bricks, Abrasives – natural and synthetic abrasives – quartz, corundum, emery, garnet, diamond, silicon carbide and boron carbide. Lubricants – mechanism of lubrication, liquid lubricants, -properties – viscosity index, flash and fire points, cloud and pour points, oilyness) – solid lubricants – graphite and molybdenum sulphide. Nanomaterials – introduction to nanochemistry – carbon nanotubes and their applicationsEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 4 UNIT-I WATER TREATMENT Introduction Water is our lifeline, played a key role not only in the history of countries, but in religion, mythology and art. Water has always been perceived as a gift from the Gods.So it rained from the heavens. Water provides the earth with the capacity of supporting life. An organism does not have to be told how important water is to their existence. An amphibian knows to lay its eggs in water or else there will be no new born. Even flies know to lay their eggs in fresh water. The only organism that does not understand the importance of water is humans especially in industrialized countries. Although water covers more than 70% of the Earth, only 1% of the earth’s water is available as a source of drinking. Yet our society continues to contaminate this precious resource. Water is known as a natural solvent. Before it reaches the consumer’s tap, it comes into contact with many different substances including organic and disease – producing contaminants that may be present in the water. Although disinfection is an important step in the treatment of potable water, they are used to prevent disease, can create byproducts which may pose significant health risks. Today, drinking water treatment at the point-of -use is no longer a luxury, it is a necessity. Occurrence: Water is the only substance that occurs at ordinary temperatures in all three states of matter: Solid, Liquid and Gas. As a so33.3.33lid, ice, it forms glaciers, frozen lakes and rivers, snow, hail and frost. It is liquid as rain and dew, and it covers three-quarters of the earth’s surface in swamps, lakes, rivers and oceans. Water also occurs in the soil and beneath the earth’s surface as a vast groundwater reservoir. As gas, or water vapour, it occurs as fog, steam and clouds. Water purification: Impurities are removed from water by seeming, sedimentation, filtration, chlorination or irradiation. Aeration removes odours and tastes caused by decomposing organic matter, industrial wastes and some gases. Various salts and metals cause hardness in water. Hardness may be removed by boiling, by adding sodium carbonate and lime or by filtering through natural or artificial zeolites. Water is also purified by processes such as desalination, reverse osmosis, electrolysis etc., Characteristics of water Water hardness Hardness = the amount of dissolved salts in water. dH ppm (or) mg /lit CaCO3 Soft 0.3 0-50Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 5 Moderately Hard Slightly Hard Moderately Hard Hard Very Hard 3-6 6 -12 12-18 18-25 25+ 50-100 100-200 200-300 300-450 >450 dH -hydrogen Power pH = the concentration of hydrogen ions in water CHARACTERISTICS OF WATER As per the suggestion given by World Health Organisation (WHO) and by Indian Council of Medical Research (ICMR), the following are the important characteristics of potable water. 1. It should be clear, colourless and odourless. 2. It should be cool and pleasant to taste. 3. It should be free from harmful bacteria and suspended impurities. 4. It should be free from dissolved gases like CO2, H2S, NH3, etc., and poisonous minerals like lead, arsenic, manganese, etc., 5. Hardness should be less than 500 ppm. 6. Chloride ion content should be less than 250 ppm. 7. Fluoride ion content should be less than 1.5 ppm. 8. Total Dissolved Solids (TDS) content should be less than 500 ppm. 9. pH of the potable water should be 6.5 – 8.5. Acidic Neutral Alkaline pH=0-7 7 pH=7-14 Chemical Characteristics of water The most important chemical characteristics of water are its acidity, alkalinity, hardness and corrosiveness. Chemical impurities can be either natural, man made (Industrial) or be deployed in raw water sources by enemy forces. Some chemical impurities cause water to behave as either an acid or a base. Since either condition has an important bearing on the water treatment process, the pH value must beEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 6 determined. Generally the pH influences the corrosiveness of the water, chemical dosages necessary for proper disinfection and the ability to detect contaminants. Hardness Hardness is caused by the soluble salts of calcium, magnesium, iron, manganese, sodium, sulphates, chlorides and nitrates. The degree of hardness depends on the type and amount of impurities present in the water. Hardness also depends on the amount of carbon-di-oxide in solution. Carbon-di-oxide influences the solubility of the impurities that cause hardness. The hardness caused by carbonates and bicarbonates is called carbonate hardness. The hardness caused by all others (chlorides, sulphates, nitrates) is called non-carbonated hardness. Hard water Water which does not produce lather with soap solution, but produces white precipitate (scum) is called hard water. In other words, water that contains mineral salts (an calcium and magnesium ions) that limit the formation of lather with soap. This is due to the presence of dissolved Ca and Mg salts. 2C17H35COONa + Ca++ (C17 H35COO)2Ca + 2 Na + Sodium soap-hardness (Calcium Soap – Water Insoluble) water soluble causing ion Soft water Water, which produces lather, readily with soap solution is called soft water. This is due to the absence of Ca and Mg salts. Water that is not hard (ie., does not contain mineral salts that interfere with the formation of lather with soap). Hardness of water How to detect hardness? Hardness of water can be detected in two ways.  When the water is treated with soap solution, if it prevents lathering and forms white scum, the water contains hardness.  Water containing hardness, gives wine red colour with Eriochrome Black –T indicator.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 7 The total water hardness (including both Ca2+ and Mg2+ ions) is read as parts per million (ppm) or weight /volume (mg/L) of Calcium Carbonate (CaCO3) in the water. Although water hardness usually measures only the total concentrations of calcium and magnesium (the two most prevalent, divalent metal ions), iron, aluminum and manganese may also be present at elevated levels in some geographical locations. The predominant source of magnesium is dolomite (CaMg (CO3)2). Types of hardness Depending upon the types of dissolved salts present in water, hardness of water can be classified into two types:  Temporary Hardness  Permanent Hardness Temporary Hardness (or) Carbonate Hardness (CH) (or) Alkaline Hardness Temporary hardness is caused by a combination of calcium and magnesium bicarbonate ions in the water. It can be removed by  boiling water  by the addition of lime (Ca(OH)2) Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution, leaving water that is softer upon coving. Ca (HCO3)2  CaCO3 ↓+ H2O + CO2 Mg (HCO3)2 + 2Ca(OH)2  Mg (OH)2↓+ 2CaCO3↓ +2H2O Permanent Hardness (or) Non – Carbonate Hardness (NCH) (or) Non – alkaline Hardness Permanent hardness is hardness (mineral content) that cannot be removed by boiling. It is usually caused by the presence of calcium and magnesium sulphates and /or chlorides which become more soluble as the temperature rises. Despite the name, permanent hardness can be removed using water – softener or ion-exchange column, where the calcium and magnesium ions are exchanged with the sodium ions in the column. It can be removed by  Lime – Soda process  Zeolite process CaCl2 + Na2CO3 →CaCO3↓ +2Nacl (Soda) CaSO4 + Na2Ze →CaZe + Na2SO4 Zeolite =(Na2 Al2 Si2 O8. X H2O)Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 8 Hard water causes scaling, which is the left-over mineral deposits that are formed after the hard water had evaporated. This is also known as lime scale. Total Hardness The sum of temporary hardness and permanent hardness. Table 1 :1 Molecular weights of some hardness producing salts. Hardness producing salt Molecular weight Hardness producing salt Molecular weight Ca(HCO3)2 162 MgSO4 120 Mg(HCO3)2 146 MgCO3 84 Mg(NO3)2 148 MgCl2 95 Ca(NO3)2 164 CaCl2 111 CaCO3 100 Ca2+ 40 CaSO4 136 Mg2+ 24 Expression of hardness in terms of equivalents of CaCO3 The concentration of hardness producing salts are usually expressed in terms of an equivalent amount of CaCO3. CaCO3 is chosen as a standard because, i) Its molecular weight (100) and equivalent weight (50) is a whole number, so the calculations in water analysis can be simplified. ii) It is the most insoluble salt, that can be precipitated in water treatment. If the concentration of hardness producing salt is x mgs/lit. then Amount x X 100 equivalent to CaCO3 Molecular weight of hardness producing salt Example If the concentration ( or) weight of CaSO4 is 43mgs/lit, then weight equivalent to 43 X 100 CaCO3 = mgs/lit 136 Units of HardnessEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 9 1. Parts per million (ppm) It is defined as the number of parts of CaCO3 equivalent hardness per 106 parts of water. 2. Milligrams per litre (mg/lit) It is defined as the number of milligrams of CaCO3 equivalent hardness per 1 litre of water. 3. Clarke’s degree (oCl) It is defined as the number of parts of CaCO3 equivalent hardness per 70,000 parts of water. 4. French degree (oFr) It is defined as the number of parts of CaCO3 equivalent hardness per 105 parts of water. Relationship between various units 1ppm = 1 mg/lit = 0.10 Fr = 0.070 Cl Problem :1 100 ml of a sample of water requires 18 ml of an EDTA solution for titration. 22 ml of the same EDTA solution was required for the titration of 100 ml of standard hard water containing I gm CaCO3 per litre. Calculate hardness of water sample in ppm. Solution Given 1 litre of std. hard water contains 1 gm of CaCO3 i.e. 1000ml of std. hard water contains 1000 mgs of CaCO3  1 ml of std. hard water = 1 mg of CaCO3 22ml of EDTA = 100 ml of std. hard water = 100 X 1 mg of CaCO3  1 ml of EDTA = 100/22 mgs of CaCO3 100 ml of sample of water = 18 ml of EDTA = 18 X 100/22 mgs of CaCO3  For 1000 ml of sample of water = 18 X 100/22 X 1000/100Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 10 Hardness = 818.18 mgs/lit or ppm. Problem : 2 0.28 gm of CaCO3 was dissolved in HCl and the solution was made upto one litre with distilled water. 100 ml of the above solution required 28 ml of EDTA solution on titration. 100 ml of hard water sample required 33 ml of same EDTA solution on titration. 100 ml of this water, after boiling cooling and filtering required 10 ml of EDTA solution on titration. Calculate the temporary and permanent harness of water. SolutionGiven 1000ml of std. hard water contains = 0.28 gm of CaCO3 Ie., 1000 ml of std. hard water contains = 0.28 X 1000 mgs oc CaCO3 = 280 mgs of CaCO3  1 ml of std. hard water = 0.28 mg of CaCO3 28 ml of EDTA = 100 ml of the std. hard water = 100 X 0.28 mgs of CaCO3 = 28 mgs of CaCO3 1 ml of EDTA =28/28=1 mgs of CaCO3 (i) Total hardness 100 ml of hard water = 33 ml of EDTA = 33 X 1 mgs of CaCO3 = 33 mgs of CaCO3  1000 ml of hard water = 33 X 1000/100 Total hardness = 330 mgs/lit (or) ppm. (ii) Permanent hardness (NCH) 100 ml of the same water, After boiling, cooling and = 10 ml of EDTAEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 11 Filtering required = 10 X 1 mgs of CaCO3 = 10 mgs of CaCO3  1000 ml of the water = 10 X 1000 mgs of CaCO3 100 Permanent hardness = 100 mgs/lit (or) ppm. (iii) Temporary hardness (CH) Temporary hardness = Total hardness – permanent hardness = 330 -100 Temporary hardness = 230 mgs/lit (or) ppm. Problem : 3 100 ml of a sample of water required 25.0 ml of 0.01 M EDTA for the titration using Eriochrome Black-_T indicator. Calculate the total hardness. Solution We know that, 1 ml 0.01 M EDTA = 1 mg of CaCO3 25 ml of 0.01 M EDTA =25 mgs of CaCO3 100 ml of sample =25.0 ml of 0.01 M EDTA Of water required = 25.0 mgs of CaCO3 equivalent  1000 ml of water is equal to = 25.0 X 1000/100 mgs of CaCO3 equivalent Total hardness = 250 mgs/lit or ppm. Problem : 4Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 12 Calculate permanent hardness from the following.: 500 ml of a water sample is boiled for 1 hr. It is then cooled and filtered. The filtrate is made up to 500 ml again with distilled water. 50 ml of this solution requires 10 ml of N/50 EDTA with EBT-indicator and NH4Cl – NH4OH buffer. Solution Given 50 ml of water sample after boiling, filtering requires 10 ml of N/50 EDTA We know that 1 ml of N50 EDTA = 1 mg of CaCO3 equivalent hardness  10 ml of N /50 EDTA = 10 mgs of CaCO3 50 ml of the boiled water sample requires = 10 ml of N/50 EDTA = 10 mgs of CaCO3  1000 ml of the water sample = 10 X 1000/50 Permanent hardness = 200 mgs/lit or ppm. Problem: 5 100 ml of a sample of water required 15.0 ml 0.01 M EDTA for titration using Eriochrome Black-T indicator. In another experiment, 100 ml of the same sample was boiled to remove the CH, the precipitate was removed and the cold solution required 8.0 ml of 0.01 M EDTA using Eriochrome Black-T indicator. Calculate (i) the total hardness (ii) permanent hardness or NCH, (iii) carbonate hardness CH, in terms of mg/lit of CaCO3 Solution We know that 1 ml of 1 M EDTA = 100 mgs of CaCO3 1 ml of 0.01 M EDTA = 1 mg of CaCO3 (i) Total Hardness 100 ml of a sample of = 15 ml of 0.01 M EDTAEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 13 Water required = 15 X 1 mgs = 15 mgs of CaCO3  1000 ml of sample of water = 15 X 1000/100 mgs of CaCO3 Is equivalent to = 150 mgs of CaCO3 equivalent Total hardness = 150 mgs/lit or ppm. (ii) Permanent Hardness (NCH) 100 ml of the same water sample = 8.0 ml of 0.01 M EDTA after boiling, filtering consumes = 8.0 X 1 mgs = 8.0 mgs of CaCO3  1000 ml of sample of = 8.0 X 1000/100mgs Water is equal to = 80 mgs of CaCO3 equivalent Permanent hardness of the = 80 ppm. Water sample (iii) Temporary Hardness Temporary hardness = Total hardness – Permanent hardness = 150 – 80 = 70 ppm Total hardness = 70 ppm Alkalinity in water Definition The pH levels in water determine if the source is more acidic or alkaline. The alkaline level of water relates to its ability to neutralize acid. A moderate percentage of alkalinity helps balance the less desirable effects of acid. Fresh water is generally more balanced with alkalinity levels of 20 – 200 mg/L. However, when water becomes too alkaline, it may taste like soda and could give a drying effect on the skin. Buffering solutionEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 14 Calcium carbonate and other such carbonate compounds provide ions to the buffering system. Without buffering solution, acid introduced in the water could alter the concentration of available hydrogen (H+). This buffer protects aquatic wildlife from rapid changes in pH levels. Ions for alkalinity Fortunately, numerous ions in water provide for a buffering solution to acid. Natural alkalinity may be due to the presence of numerous ions including hydroxide, carbonate and bicarbonates. Alkalinity or AT is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. The alkalinity is equal to the stoichiometric sum of the bases in solution. In the natural environment, carbonate alkalinity tends to make up most of the total alkalinity due to the common occurrence and dissolution of carbonate rocks and presence of CO2 in the atmosphere. Other natural components include borate, hydroxide, phosphate, silicate, nitrate, dissolved ammonia. Determination of alkalinity The alkalinity producing ions can be determined by titrimetry using standard acid and phenolphthalein and methyl orange as indicators. The determination is based on the following reactions. i. [OH-] + [H+]  H2O ii. [CO32-] + [H+] ( HCO3-) iii. [HCO3-] + [H+]  H2O+CO2 Types of alkalinity 1. Hydroxide alkalinity ------due to [OH-] 2. Carbonate alkalinity -------due to [CO32-] 3. Bicarbonate alkalinity ------due to [HCO3-] Detection of various Alkalinity Titration I Known amount of water sample is titrated against a standard acid using phenolphthalein indicator, the end point indicates the completion of the reaction (i) and (ii) i.e. neutralization of OHaan CO32-ions. Thus the amount of acid used corresponds to sum of hydroxide and one-half of the carbonates present.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 15 Titration II Similarly the same amount of water sample is titrated against a standard acid using methyl orange indicator, the end point indicates the completion of reaction (i), (ii) and (iii). The amount of acid used after the phenolphthalein end point corresponds to sum of one half of normal carbonate and all the bicarbonates. The total amount of acid used (amount of acid upto phenolphthalein end point + amount of acid methyl orange end point) represent the total alkalinity (due to hydroxide, the carbonate and bicarbonates). i.e., neutralisation of OH-, CO32-and HCO3-ions. Note: OH-and HCO3-ions cannot exist together in water, because they combine instantaneously to form CO32-ions i.e., OH-+ HCO3-CO32-+ H2O e.g. NaOH + NaHCO3 Na2CO3 + H2O Thus in water all the three ions (OH-, CO32-, HCO3-) cannot exist together. Determination of various types of Alkalinity Various steps involved in the determination of various types of alkalinity are as follows. Step I: Experimental Procedure Titration I : Determination of Phenolphthalein Alkalinity Pipette out 100 ml of the given water sample into a clean conical flask. Add 2 to 3 drops of a phenolphthalein indicator and titrate it against N/50 H2SO4 taken in the burette. The end point is the disappearance of pink colour. Let the volume of acid consumed be V1 ml Titration II: Determination of Methyl Orange Alkalinity After the titration, to the same solution, add 2 to 3 drops of methyl orange indicator, and continue the titration against the same N/50 H2SO4 . The end point is the reappearance of pink colour.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 16 Let the volume of acid consumed be V2 ml Step II Calculation (i) Calculation of Phenolphthalein Alkalinity The volume of acid used to = V1 ml Phenolphthalein end point Normality of the acid N2 = N/50 Volume of the water sample V2 = 100 ml Normality of water sample N2 = ? According to volumetric law V1 N1 = V2 N2 N2= V1N1 /V2 N2= V1 /50 X 1/50  Phenolphthalein alkalinity (P) (in terms of CaCO3 equivalent) = N2 X Eq. wt of CaCO3 X 1000 ppm = V1 X 50/100 X 1000/50 ppm P = 10V1ppm (ii) Calculation of Methyl Orange Alkalinity Extra volume of acid used to methyl = V2 ml orange end point Total volume of acid used to methyl = (V1 + V2) mlEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 17 orange end point let, the volume of acid used to methyl V1 = (V1 + V2) ml orange end point Normality of the acid N1 = N50 Volume of the water sample V2 = 100 ml Normality of water sample N2 = ? According to Volumetric law N2 = (V1 + V2)/100 X 1/50  Methyl orange alkalinity (M) (in terms of CaCO3 equivalent) = (V1 + V2) X 50/100 X 1000/50 ppm M=10(V1+V2)ppm Conclusions (i) When P = 0, both OH-and CO32-are absent and alkalinity is due to HCO3-only. (ii) When P = ½ M, only CO32-is present, half of carbonate neutralization reaction takes place (i.e., CO32-+ H + HCO3-) with phenolphthalein indicator. Complete carbonate neutralization reaction (i.e., CO32-+ H+ HCO3-HCO3-+ H+ H2O +CO2) occurs when methyl orange indicator is used. thus alkalinity due to CO32-= 2P. (iii) When P = M, only OH-is present, alkalinity due to OH-= P = M. (iv) When P > 1/2M, besides CO32-, OH-ions are also present. Now half of CO32-is (i.e., HCO3-H+ ----- CO2 + H2O ) equal to (M –P) So, alkalinity due to complete CO32-= 2 (M – P)  Alkalinity due to OH-= M – 2 (M –P) = (2P – M).Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 18 (v) When P < ½ M, besides CO32-, HCO3-ions are also present. Now alkalinity due to CO32-= 2P  Alkalinity due to HCO3-= (M – 2P) The data of the above conclusions are tabulated as follows Calculation of Alkalinity of Water Results of P end point and P & M end point OH-(ppm) CO32-(ppm) HCO3-(ppm) Nature of alkalinity P = 0 0 0 M Only bicarbonate P = ½ M 0 2P 0 Only carbonate P<1/2 M 0 2P (M – 2P) bicarbonate and carbonate P>1/2 M (2P – M) 2(M – P) 0 Hydroxide and carbonate P =M P =M 0 0 Only hydroxide Estimation of hardness by EDTA method EDTA is Ethylene Diamine Tetra Acetic Acid. The structure of EDTA is Since EDTA is insoluble in water, its disodium salt is used as a sequestering or complexing agent. Principle The amount of hardness causing ions. (Ca2 + and Mg2+) can be estimated by titrating the water sample against EDTA using Eriochrome Black-T (EBT) at a pH of 8 – 10. In order to maintain the pH, buffer solution (NH4Cl – NH4OH mixture) is added. Only at this pH such a complexation is possible.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 19 When the EBT indicator is added to the water sample, it forms wine red coloured weak complex, with Ca2+ and Mg2+ ions. Ca2+ Mg2+ + EBT pH = 8 – 10 Ca EBT Complex Mg wine red coloured weak complex When this solution is titrated against EDTA, it replaces the indicator from the weak complex form stable EDTA complex. When all the hardness causing ions are complexed by EDTA, the indicator is set free. The colour of the free indicator is steel blue. Thus the end point is the change of colour from wine red to steel blue. Ca Mg EBT Complex + EDTA pH=8-10 Wine red coloured weak complex Ca EDTA Complex + EBT Mg (Steel Blue) STANDARDIZATION OF EDTA The burette is filled with the EDTA solution. 20ml of standard hard water is pipetted out into a clean conical flask. Add 10-15 ml of buffer solution and a few drops of EBT indicator. The wine red coloured solution in the conical flask is titrated against the EDTA taken in the burette. At the end point the wine red colour is changed to steel blue colour. Repeat the titration for getting concordant titre values. Calculation 1 ml of standard hard water = 1 mg of calcium carbonate hardness Volume of standard hard water = 20ml = 20 mg of calcium carbonate hardness Volume of EDTA = V1mlEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 20 V1 ml of EDTA = 20mg of calcium carbonate hardness 1 ml of EDTA =20/V1 mg of calcium carbonate equivalent Titration – II ESTIMATION OF TOTAL HARDNESS The burette is filled with the EDTA solution. 20ml of sample hard water is pipetted out into a clean conical flask. Add 10-15 ml of buffer solution and a few drops of EBT indicator. The wine red coloured solution in the conical flask is titrated against the EDTA taken in the burette. At the end point the wine red colour is changed to steel blue colour. Repeat the titration for getting concordant titre values. Calculation 1 ml of EDTA = 20/V1 mg of calcium carbonate equivalent Volume of sample hard water = 20 ml Volume of EDTA = V2 ml = V2 (20/V1) mg of calcium carbonate hardness equivalent 50 ml of sample hard water = V2 (20/V1) mg of calcium carbonate hardness equivalent 1000 ml of sample hard water = (V2/V1) X 1000 mg of calcium carbonate hardness equivalent Total hardness =(V2/V1) X 1000 mg of calcium carbonate hardness equivalent ESTIMATION OF PERMANENT HARDNESS The water sample of 250 ml is taken in the beaker and evaporated nearly to 50 ml. The temporary hard salts are settled down. Filtered and washed thoroughly and made up the solution to 250ml. Pipetted out 20 ml of the made up solution. Buffer solution and EBT indicator are added and titrated against the EDTA taken in the burette. End point is the change of colour from wine red to steel blue. Repeat the titration for getting concordant titre values.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 21 Calculation 1 ml of EDTA = 20/V1 mg of calcium carbonate equivalent Volume of sample hard water = 20 ml Volume of EDTA = V3 ml = V3 X (50/V1) mg of calcium carbonate hardness equivalent 20 ml of sample hard water = V3X (20/V1) mg of calcium carbonate hardness equivalent 1000 ml of sample hard water = (V3/V1) X 1000 mg of calcium carbonate hardness equivalent Permanent hardness =(V3/V1) X 1000 mg of calcium carbonate hardness equivalent TEMPORARY HARDNESS Temporary Hardness = total hardness – permanent hardness = [(V2 /V1) x 1000] -[(V3/V1) x 1000] mg of calcium carbonate Equivalent Domestic Water Treatment Water for domestic use: The specification of water for drinking purpose is as follows: 1. The water should be clear, colourless and odourless 2. The water should be free from dissolved gases such as CO2,H2S etc., 3. The water should be free from pathogenic (disease – producing) micro-organisms. 4. The water should not be excessively hard or soft. The recommended maximum concentration of hardness is 125 ppm. 5. The pH of the drinking water must be 7.0 – 8.5. 6. The turbidity in drinking water should not exceed 25 ppm. 7. The recommended maximum concentration of total dissolved solid in drinking water should be 500 ppm .Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 22 Purification or Treatment of water for Municipal supply The various stages in the treatment of water for municipal supply involves the following steps: 1. Screening 2. Aeration 3. Sedimentation 4. Coagulation. 5. Filtration 6. Sterilisation and Disinfection 7. Storage and distribution It is represented clearly in the following flow chart: 1. 2. Screening It is a process of removing the floating materials like, leaves, wood pieces etc., from water. The raw water is allowed to pass through a screen, having large number of holes which retains the floating materials and allows the water to pass. Aeration Aeration of water promotes taste and odour by exchange of gases between the water and atmosphere. The main purpose of aeration is a) To add or increase the content of oxygen in water. b) To remove CO2, H2S and other volatile substances causing bad taste and odour in water. c) To remove the impurities like Fe and Mn (which are precipitated as their respective Ferrric and Mangenic hydroxides or other salts. SedimentationThe suspended and colloidal impurities which can settle at the bottom are separated in a sedimentation tank by gravitation. The main principle of sedimentation is to allow water to rest (for 6 hrs.) so that the heavier particles settle down due to gravity. Sedimentation removes only 75% of the suspended impurities. Coagulation However fine particles like clay, silica, etc., take many hours or sometimes days to settle down. So certain chemicals are added to aid sedimentation. This process is called coagulation. The common coagulants (chemicals) used are generally salts of aluminium. (alum Screening Filtration Coagulation Sedimentation AerationSterilization /Disinfection Municipal SupplyEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 23 {K2SO4.Al2(SO4)3.24H2O}Sodium aluminate NaAlO2 and salts of iron (Ferrous sulphate, ferric sulphate, ferric chloride). When a coagulant is added to the water and mixed thoroughly, a thick gelatinous precipitate is formed which is insoluble in water. This precipitate is called flock. As this flock settles down, it attracts and arrests the colloidal particles and bring them down 1) Al2 (SO4)3 +Ca(HCO3 )2 2Al(OH)3 + 3CaSO4 + 6CO2 ( Coagulant) aluminium floculant ppt. aluminium sulphate hydroxide 2) FeSO4 + Mg(HCO3)2 Fe(OH)2 + MgCO3 + CO2 +H2O (coagulant) 4 Fe(OH)2 +O2 +2H2O 4Fe(OH)3 dissolved Ferric hydroxide oxygen (heavy floc) Fe (OH)3 is in the form of heavy floc, which causes, quick sedimentation. FILTRATION It is the process of removing bacteria, colour, taste, odour and suspended particles, etc., by passing the water through filter beds containing free sand, coarse sand and gravel. A typical sand filter is shown in fig. The sand filter consists of a tank containing a thick top layer of fine sand followed by coarse sand, fine gravel and coarse graval. When the water passes through the filtering medium, it flows through the various beds slowly. The rate of filtration decreases slowly due to the clogging of impurities in the pores of the sand bed. When the rate of filtration becomes very slow, the filtration is stopped and the thick top layer of fine sand is scrapped off and replaced with clean sand. Bacteria are also partly removed by the process.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 24 Sterilization or Disinfection The process of destroying /killing the disease producing bacteria, micro-organisms, etc., from the water and making it safe for use, is called disinfection. The chemicals or substances, which are added to water for killing the bacteria, etc., are known as disinfectants. Methods of sterilization Sterilization can be carried out by the following methods. By Boiling: Disadvantages: 1) This process can kill only the existing germs at the time of boiling, but does not provide any protection against future possible contamination. 2) This method is very costly and can be used only in individual cases particularly during the break up of epidemics in the town or city. By ozonation (using Ozone) Ozone is a powerful disinfectant and is readily absorbed by water. Ozone produced by passing silent electric discharge through cold and dry oxygen. 3O2 Silent electric 2O3 Discharge Ozone is highly unstable and breaks down to give nascent oxygen. O3 O2 + [O] Nascent oxygen The nascent oxygen is a powerful oxidizing agent and kills the bacteria as well as oxidizes the organic matter present in water. For carrying out the disinfection by ozone, ozone is released /injected into the water and the two are allowed to come in contact in a sterilizing tank. The disinfected water is removed from the top and the contact period is about 10 – 15 minutes. Advantages: 1) Disinfection by ozone is costlier than chlorine, but it simultaneously removes colour, odour and taste without giving any residue. 2) Its excess is not harmful, since it is unstable and decomposes into oxygen. By using ultra-violet radiations 1) UV rays are produced by passing electric current through mercury vapour lamp. This is particularly useful for sterilizing water in swimming pool. 2) In this process U.V. light from mercury lamp enclosed by quartz globe is focused on flowing water. Disadvantages: 1) The U.V. radiation effectively destroys the bacteria but it is found to be a costlier process when applied to larger quantities of water.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 25 2) In this process turbid water cannot be treated (when turbidity is greater than 15ppm) By Chlorination: (a) Cl2 + H2O HCl + HOCl (Hypochlorous acid) powerful germicide HOCl HCl + (O) Nascent oxygen For filtered water 0.3 to 0.5 ppm chlorine can be added and the treated water should not contain more than 0.2 ppm free chlorine. By adding Chloramine When chlorine and ammonia are mixed in the ratio 2:1, a compound chloramine is formed. Cl2 + NH3 CINH2 + HCl Chloramine CINH2 + H2O HOCl + NH3 Disinfectant Chloramine compounds decompose slowly to give chlorine. It is a better disinfectant than chlorine. Chloramine gives good taste to the treated water. By adding bleaching power When bleaching powder is added to water, it produces hypochlorous acid (HOCl). HOCl is a powerful germicide. CaOCl2 + H2O Ca(OH)2 + Cl2 Bleaching powder Cl2 + H2O HCl + HOCl Hypochlorous acid HOCl + Bacteria Bacteria are killed Disadvantages: 1) Bleaching powder introduces calcium in water, thereby making it more hard. 2) It has to be analysed for its effective chlorine content due to its continuous decomposition during storage. 3) Only calculated quantity of bleaching powder should be used since an excess of it gives a bad taste and smell to treated -water. Mechanism The death of micro-organisms, bacteria etc., results from chemical reaction of hypochlorous acid with the enzymes in the cells of the organisms etc., Since enzyme is essential for the metabolic processes of the micro-organisms, so death of micro – organisms results due to inactivation of enzyme (in the cells of organisms) by hypochlorous acid. Liquid chlorine is most effective when applied to filtered water at such a point where adequate mixing is done. Apparatus used for this purpose is known as chlorinator, which is a high tower, having a number of baffle plates. Water and proper quantity of concentrated chlorine solution are introduced at its top. During their passage through the tower, they get thoroughly mixed. The treated – water is taken out from the bottom. For filtered-water, about 0.3 to 0.5 ppm of chlorine is sufficient.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 26 -----------------------------------------------------------------------------------------------------Advantages of chlorine i. It is effective and economical ii. It is stable and does not deteriorate on keeping. iii. It can be used at low as well as high temperatures. iv. It introduces no salt impurities in the treated water. v. It is most ideal disinfectant. Disadvantages: i. Excess of chlorine, if added, produces a characteristic unpleasant taste and odour. Its excess produces an irritation on mucus membranes ii. It is more effective below 6.5 pH and less effective at higher pH values HOCl  H+ + OCl-Hypochlorite ion This is due to the fact that HOCl is about 80 times more destructive to bacteria than OCl(-) ions. OCl(-) ions cannot combine with enzymes in the cells of microorganisms and so less effective at higher pH values. Break Point Chlorination: Water contains the following impurities (i) Bacteria (ii) Organic impurities. (iii) Reducing substances (Fe2+, H2S etc.,). (iv) Free ammonia Formation of chloramine & chloro compound s Destruction of chloramine & chloro compounds Residual chlorine Applied chlorine Kill the bacteria & oxidation of reducing compounds of chlorineEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 27 Chlorine may be added to water directly as a gas or in the form of bleaching powder. When chlorine is applied to water, the results obtained can be depicted graphically in the fig. 1.2. The graph shows the relationship between the amount of chlorine added to water and the residual chlorine.It is seen from the graph that initially the applied chlorine is used to kill the bacteria and oxidises all the reducing substances present in the water and there is no free residual chlorine. As the amount of applied chlorine increases, the amount of combined residual chlorine also increases. This is due to the formation of chloramines and other chloro compounds. At one point, on further chlorination, the oxidation of chloramines and other impurities starts and there is a fall in the combined chlorine content. Thus the combined residual chlorine decreases to a minimum point at which oxidation of chloramines and other impurities complete and free residual chlorine begins to appear. This minimum point is known a “break point chlorination”. Thus, the break point chlorination eliminates bacteria, reducing substances, organic substances responsible for the bad taste, and odour from the water. Boiler Feed water The water fed into the boiler for the production of steam is called boiler feed water. Boiler feed water should be free from turbidity, oil, dissolved gases, alkali and hardness causing substances. If hard water obtained from natural sources is fed directly into the boilers, the following troubles may arise. Boiler troubles (or) disadvantages of using hardwater in boilers 1. Scale and sludge formation. 2. Priming and foaming (carry over), 3. Caustic embrittlement. 4. Boiler corrosion. Scale and sludge formation in boilers When water is continuously converted into steam in boilers, the concentration of dissolved salts in water increases progressively. When the concentration of the salts reaches their saturation point, they are thrown out in the form of precipitates on the inner walls of the boilers. The least soluble one gets precipitated first.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 28 SludgeIf the precipitate is loose and slimy it is called sludge. Sludges are formed by substances like MgCl2, MgCO3, MgSO4 and CaCl2. They have greater solubility in hot water than cold water. Scale On the other hand, if the precipitate forms hard and adherent coating on the inner walls of the boiler, it is called scale. Scales are formed by substances like Ca(HCO3)2, CaSO4 and Mg(OH)2. S. No. Sludge Scale Sludge is a loose, slimy and non-adherent precipitate. Scale is a hard, adherent coating The main sludge forming substances are MgCO3, MgCl2, MgSO4 and CaCl2 etc.,` The main scale forming substances are Ca(HCO3)2, CaSO4, Mg(OH)2. 3Disadvantages: Sludges are poor conductors of heat. Excess of sludge formation decreases the efficiency of boiler. Disadvantages: Scales act as thermal insulators. It decreases the efficiency of boiler. Any crack developed on the scale, leads to explosion. 4Prevention (i) Sludge formation can be prevented by using softened water. Prevention (i) Scale formation can be prevented by dissolving using acids like HCl, H2SO4. (ii) Sludges can also be removed by “blow – down operation” (ii) Scale formation can be removed by (a) External treatment (b) Internal treatment (iii) Blow-down operation is a process of removing a portion of concentrated water by fresh water frequently from the boiler during steam production. (iv) They can also be removed by applying thermal shocks, scrapers, wire brush etc., Ca (HCO3)2 present in hard water decomposes at higher temperature producing CaCO3. Ca (HCO3) CaCO3 + H2O + CO2 Calcium sulphate gets deposited in the boilers since the solubility of the salt decreases with increase in temperature. CaSO4 gets deposited on the heated portion of the boiler. Magnesium hydroxide Mg (OH)2 is produced in the boiler by the hydrolysis of MgCl2 salt MgCl2 + H2O  Mg (OH)2 + 2 HCl Removal of scales (i) Scales can be removed by applying thermal shocks (sudden heating and cooling) (ii) Using scrapers, wire brush etc., (iii)Using certain chemicals, scales can be removed.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 29 For example, using 5 – 10% HCl , Calcium carbonate scales can be removed. CaSO4 scales can be removed using EDTA. (iv)By “blow down operation” (removing the bottom portion of salt concentrated water of the boiler) the scale formation can be avoided. Disadvantages of scale formation 1. Wastage of fuel 2. Lowering of boiler safety 3. Decrease in efficiency 4. Danger of explosion Wastage of fuel Scales have a low thermal conductivity, so the rate of heat transfer from boiler to inside water is greatly decreased. In order to provide a steady supply of heat to water, excessive or overheating is done and this causes increase in fuel consumption. Lowering of boiler safety Due to scale formation, over heating of boiler is to be done in order to maintain a constant supply of stream. The overheating of the boiler tube makes the boiler material soften and weaker. Decrease in efficiency Scales may sometimes deposit in the valves and condensers of the boiler and choke them partially. This results in decrease in efficiency. Danger of explosion When thick scales crack, due to uneven expansion, the water comes suddenly in contact with over -heated iron plates. So sudden high -pressure is developed which may even cause explosion of the boiler. Disadvantages of sludge formation  Sludges are poor conductor of heat. So they tend to waste a portion of heat generated.  If sludges are formed along with scales, then former gets entrapped in the latter and both get deposited as scales.  Excessive sludge formation disturbs the working of the boiler, causing even chocking of the pipes. Priming of Foaming Priming When a boiler is steaming (ie producing steam) rapidly, some particles of the liquid water are carried along with the steam. This process of “ Wet steam” formation is called priming. These droplets of liquid water carry with them some dissolved salts and suspended impurities. This phenomenon is called “carry over”. It occurs due to priming and foaming. Priming is caused by. a. The presence of large amount of dissolved solids.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 30 b. High steam velocities c. Sudden boiling d. Improper boiler design e. Sudden increase in steam-production rate Prevention a. Fitting mechanical steam purifiers b. Avoiding rapid change in steaming rate c. Maintain low water levels in boiler and d. Efficient softening and filtration of the boiler – feed water. Foaming The formation of stable, persistent foam or bubbles in boilers above the surface of water is called foaming. These bubbles are carried over by steam , leading to excessive priming. Foaming is caused by the a. Presence of oil and grease b. Presence of finely divided particles Disadvantages 1) Dissolved salts carried by the wet steam to super heater and turbine blades, where they get deposited and thus reduces their efficiency. 2) Dissolved salts may enter the parts of other machinery, thereby decreasing the life of the machinery. 3) Actual height of the water column cannot be judged properly, thereby maintaining the boiler pressure becomes difficult. Prevention Foaming can be prevented by 1) adding coagulants like sodium aluminates, aluminium hydroxide etc., 2) adding anti – foaming agents like synthetic polyamides. Caustic Embrittlement Caustic embrittlement means inter – crystalline cracking of boiler metal. Caustic embrittlement is a type of boiler corrosion, caused by using highly alkaline water in the boiler. During softening process by lime –soda process, free Na2CO3 is usually present in small proportion in the softened water. In high pressure boilers, Na2CO3 decomposes to give sodium hydroxide and carbon-di -oxide. Na2CO3 + H2O 2NaOH + CO2 And this makes the boiler water “Caustic”. This NaOH flows into the minute hair cracks and crevices usually present on the boiler material by capillary action and dissolves the surrounding area of iron as sodium ferrate. Fe + 2NaOH -- Na2 FeO2 + H2O Sodium FerrateEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 31 This causes brittlement of boiler parts, particularly stressed parts like bends, joints, rivets etc., causing even failure of the boiler. Prevention Caustic embrittlement can be prevented by 1) Using sodium phosphate as softening agent instead of sodium carbonate. 2) By adding tannin, lignin to the boiler water, which blocks the hair cracks. 3) Neutralising the alkali with a very small quantity of acid. Boiler Corrosion Boiler corrosion is decay of boiler material by a chemical or electro –chemical attack by its environment. Corrosion in boilers is due to the presence of the following 1. Dissolved oxygen 2. Dissolved Carbon dioxide 3. Dissolved salts Dissolved oxygen: Dissolved oxygen in water is mainly responsible for the corrosion of boiler. The dissolved oxygen in water attacks the boiler material at higher temperature. 4 Fe + 6 H2O + 3 O2 4 Fe (OH) 3 Removal of dissolved oxygen: Dissolved oxygen can be removed by two methods 1. Chemical method 2. Mechanical De-aeration Chemical method: Sodium sulphite , hydrazine are some of the chemicals used to remove dissolved oxygen 2 Na2SO3 + O2 Na2SO4 N2H4 + O2 N2 + 2H2O Hydrazine is found to be an ideal compound for removing DO in the water, since the products are water and inert N2 gas. Mechanical De-aeration DO can be removed by mechanical de-aeration. In this method water is entered and fall slowly into perforated plates fitted inside the tower and are heated, and a vacuum is created by the suction pump. The high and low temperatures produced inside the tower which reduce the DO content in water.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 32 Dissolved Carbon dioxide It produces carbonic acid with water, which is acidic and corrosive in nature. CO2 + H2O H2 CO3 CO2 gas is also produced from the decomposition of bicarbonate Ca (HCO3)2  CaCO3 ↓+ H2O + CO2 Removal of Dissolved Carbon dioxide CO2 can be removed by adding calculated amount of NH4OH 2 NH4OH + CO2 (NH4)2 CO3 + H2O Both carbon dioxide and oxygen can be removed by mechanical deaeration process. Dissolved salts Acids, produced from salts in water are also mainly responsible for the boiler corrosion. Salts like MgCl2, CaCl2 etc, which undergo hydrolysis even at high temperature to produce HCl, will corrode the boilers. MgCl2 + 2H2O Mg(OH)2 + 2HCl Fe + 2HCl FeCl2 + H2Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 33 FeCl2 +2H2O Fe(OH)2 + 2HCl Removal of acids: Boiler corrosion by dissolved salts is removed by adding alkali to the water. HCl + NaOH NaCl + H2O SOFTENING OR CONDITIONING METHOD Water used for industrial purposes should be free from hardness producing substances, suspended impurities and dissolved gases etc. The process of removing hardness producing salts from water is known as softening (or) conditioning of water. Softening of water can be done in two methods 1. External conditioning. 2. Internal conditioning. INTERNAL CONDITIONING OR INTERNAL TREATMENT OR BOILER COMPOUNDS It involves the removal of scale forming substance, which were not completely removed in the external treatment, by adding chemicals directly into the boiler. These chemicals are also called boiler compounds. Carbonate conditioning Scale formation can be avoided by adding Na2CO3 to the boiler water. It is used only in low pressure boilers. The scale forming salt like CaSO4 is converted into CaCO3, which can be removed easily. CaSO4 + Na2CO3 CaCO3 + Na2SO4. Phosphate conditioning Scale formation can be avoided by adding sodium phosphate. It is used in high pressure boilers. The phosphate reacts with Ca2+ and Mg2+ salts to give soft sludges of calcium and magnesium phosphates. 3CaSO4 + 2 Na3PO4 Ca3(PO4)2 + 3Na2SO4 Generally 3 types of phosphates are employed.  Trisodium phosphate – Na3PO4 (Too alkaline) – used for too acidic water.  Disodium hydrogen phosphate -Na2HPO4 (weakly alkaline) -used for weakly acidic water.  Sodium dihydrogen phosphate -NaH2PO4 (acidic ) – used for alkaline water. Calgon conditioningEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 34 Calgon is sodium hexa meta phosphate Na2[Na4(PO3)6]. This substance interacts with calcium ions forming a highly soluble complex and thus prevents the precipitation of scale forming salt. 2CaSO4 + Na2[Na4(PO3)6] Na2[Ca2(PO3)6] + 2 Na2SO4. The complex Na2[Ca2(PO3)6] is soluble in water and there is no problem of sludge disposal. EXTERNAL CONDITIONING It involves the removal of hardness producing salts from the water before feeding into the boiler. The external treatment can be done by the Demineralisation or Ion exchange process. Ion Exchange (Or) Demineralisation Process This process removes almost all the ions (both anions and cations) present in the hard water. The soft water, produced by lime-soda and zeolite processes, does not contain hardness producing Ca2+ and Mg2+ ions, but it will contain other ions like Na+, K+ , SO42-, Cl-etc.,. On the other hand D.M. (Demineralised) water does not contain both anions are cations. Thus a soft water is not demineralised water whereas a demineralised water is soft water. This process is carried out by using ion exchange resins, which are long chain, cross linked, insoluble organic polymers with a micro porous structure. The functional groups attached to the chains are responsible for the ion exchanging properties.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 35 Cation exchanger Resins containing acidic functional groups (-COOH, -SO3H) are capable of exchanging their H+ ions with other cations of hard water. Cation exchange resin is represented as RH2 Examples: (i) Sulphonated coals. (ii) Sulphonated polystyrene R – SO3H ; R – COOH = RH2 Anion Exchanger Resins containing basic functional groups (-NH2, -OH) are capable of exchanging their anions with other anions of hard water. Anion exchange resin is represented as R (OH)2. Examples: (i) Cross – linked quaternary ammonium salts. (ii) Urea-formaldehyde resin. R – NR3OH ; R – OH ; R-NH2 = R(OH)2 PROCESS The hard water is first passed through a cation exchange column, which absorbs all the cations like Ca2+ , Mg2+ , Na+, K+, etc., present in the hard water RH2 + CaCl2 RCa + 2HCl RH2 + MgSO4 RMg + H2SO4 RH + NaCl RNa + HCl The cation free water is then passed through an anion exchange column, which absorbs all the anions like Cl-, SO42-, HCO3-etc., present in the water. R’(OH)2 + 2HCl R’ Cl2 +2H2O R’(OH)2 + H2SO4 R’SO4 + 2H2O The water coming out of the anion exchanger is completely free from cations and anions. This water is known ad dematerialized water or deionized water. Regeneration When the cation exchange resin is exhausted, it can be regenerated by passing a solution of dil HCl or dil H2SO4. RCa + 2HCl RH2 + CaCl2 RNa + HCl RH + NaCl Similarly, when the anion exchange resin is exhausted, it can be regenerated by passing a solution of dil NaOH. R’Cl2 + 2NaOH R’(OH)2 + 2NaCl Advantages of ion-exchange processEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 36 (i) Highly acidic or alkaline water can be treated by this process. (ii) The water obtained by this process will have very low hardness (nearly 2 ppm) Disadvantages of ion-exchange process  Water containing turbidity, Fe and Mn cannot be treated, because turbidity reduces the output and Fe, Mn form stable compound with the resin.  The equipment is costly and more expensive chemicals are needed. Desalination The process of removal of dissolved salts (NaCl) from water is called desalination or desalting. Water containing high concentrations of dissolved salts /solids is known as brackish water. The salinity of raw water is expressed in mg/L or ppm of dissolved salts. Water quality is usually graded as i) Fresh water (less than 100 mg /L of dissolved salts) ii) Brackish water ( 1000 – 35000 mg /L of dissolved salts) iii) Sea water (greater than 35000 mg/L of dissolved salts) The following techniques are carried out for desalination of sea water and brackish water. a. Reverse Osmosis b. Electrodialysis c. Distillation etc., Reverse osmosis When two solutions of different concentrations are separated by a semi-permeable membrane, solvent (water) flows from a region of lower concentration to a region of higher concentration. This spontaneous process is called osmosis. The excess pressure applied on the concentrated solution side to prevent osmosis is called osmotic pressure. This natural process can be reversed by applying a pressure higher than the osmotic pressure of the order of 15 – 40 kg /cm2 on the saturated solution side. In otherwords, to force the fresh water to move from the concentrated to the dilute side through the semi permeable membrane is called reverse osmosis. This process is also known as super-filtration or hyper filtration. Cellulose acetate polyamide, and ployamide sulphone are the polymers used for the semi-permeable membrane. Poly acrylonitrile (PAN), polysulphoneEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 37 The latest technique of this method is solar powered membrane distillation (SMPD). In this process hydrophobic membranes are used. These membranes allow all the water vapour in gaseous state to pass through while preventing liquid water with salt. Advantages 1) The water obtained by this process is used for high pressure boilers. 2) Due to low capital and operating cost and high reliability this process is used for converting sea water into drinking water. 3) The life time of the membrane is high and it can be replaced within a short time. 4) It also removes ionic, non-ionic and colloidal impurities. QUESTION BANK Part – A 1. Distinguish any two differences between hard water and soft water? (au jan10) 2. Name the gases dissolved in water that cause corrosion? (au jan10) 3. How is exchange resins regenerated? (au jan10) 4. What is phosphate conditioning?(au jan10) 5. Calculate the hardness of a water sample containing 2.4mg of CaCl2 in 500ml in water? (au jan10) 6. What is calgon? how does it function in water treatment(au jan09) 7. What is disinfection? Give any two examples(aug 07) 8. What is caustic embrittlement? how can it be prevented 9. Expand EDTA? write the structure of Ca-EDTA complex 10. Explain UV treatment for domestic water? (au jan10) 11. What is non-carbonate hardness? 12. Define desalination? 13. What will be the hardness of solution containing 0.586 gm of NaCl and 0.6gm of MgSO4 (Jan 09) 14. How is the exhausted zeolite softener bed regenerated?(aug 09) 15. Explain what is meant by soft water /hard water (j 09) 16. What is meant by disinfectant? What is the advantage of using chloramines as a disinfectant? 17. Why is hardness expressed in terms of CaCO3 equivalent?(j 09) 18. What is reverse osmosis? (au 09) 19. Distinguish between softening and demineralization? (au 06) 20. Discuss the causes and prevention of priming and foaming? (au 06) 21. What is breakpoint chlorination? state its significance(au 05) 22. What is blow down operation? 23. What is meant by boiler corrosion? How it is prepared? 24. What is meant by carry over? How is it caused 25. Compare phosphate conditioning with calgon conditioning? 26. Why NH4Cl-NH4OH buffer is used in EDTA titration?Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 38 27. What is meant by priming and foaming? what are their effects in boiler Part – B 1. How is temporary hardness of water estimated by EDTA method? 2. What are the requirements of potable water? how will you purify it for drinking purpose 3. What are ion exchange resins? how are they useful in removing hardness of water 4. What is desalination ?With a neat diagram describe the method for the desalination of brackish water 5. a) 50ml of sample of hard water required 35ml of 0.01m EDTA .calculate total hardness and temporary hardness of water. b) What are scales and sludges? What are their disadvantages? c) What is calgon? Why is calgon conditioning better than phosphate conditioning. 6. a) How will you determine alkalinity? b) If a sample of water contains 50mg of MgCl2 .Calculate the hardness treatment of CaCO3 eq. c) What are the requirements for boiler feed water. 7. a) Discuss the disadvantages of using the hardwater in boilers? b) Give an account of internal treatment of boiler water. 8. a) How is hardness of water determined by EDTA method b) Explain the following boiler troubles suggesting the remedial method i. Sludge and scale formation ii. Caustic embrittlement 9. Explain how demineralization of water is done in water technology? 10. What is potable water? What are the steps taken to obtain pure drinking water? 11. What are boiler troubles? how are they caused ?Suggest steps to minimize boiler troubles (2 MARK QUESTIONS&ANSWERS) 1. How is alkalinity classified? Depending upon the anion present in water, alkalinity is classified in to 3 types.  Hydroxide alkalinity(OH-)  Carbonate alkalinity (CO32-)  Bicarbonate alkalinity (HCO3-) 2. What are the disadvantages of scale formation? Scales act as thermal insulators. It decreases the efficiency of boiler. Any crack developed on the scale, leads to explosion. 3. What is meant by priming and foaming? How can they be prevented? Priming is the process of production of wet steam. Priming can be prevented by controlling the velocity of steam and keeping the water level lower.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 39 Foaming is the formation of stable bubbles above the surface of water. Foaming can be prevented by adding coagulants like sodium aluminate and antifoaming agents like synthetic polyamides. 4. What is meant by caustic embrittlement? How is it prevented? Caustic embrittlement means intercrystalline cracking of boiler metal. Prevention Caustic embrittlement can be prevented by (i) Using sodium phosphate as softening agent in stead of sodium carbonate. (ii) By adding tannin, lignin to the boiler water, which blocks the hair cracks. 5. Indicate the reasons for boiler corrosion Boiler corrosion arises due to the presence of (i) dissolved oxygen, (ii) dissolved carbon dioxide, (iii) dissolved salts. 6. Define softening of water. How is it carried out? The process of removing hardness producing salts from water is known as softening (or) conditioning of water. Softening of water can be done in two methods 1. External treatment. 2. Internal treatment. 7. What are the advantages of ion-exchange process (i) Highly acidic or alkaline water can be treated by this process. (ii) The water obtained by this process will have very ;low hardness (nearly 2 ppm). 8. How is water demineralised in an ion-exchanger? When the water containing ions (both anion and cation) are passed through ion exchange columns, it absorbs all the ions (anions and cations) as shown below. Cation exchanger: RH2 + CaCl2 →RCa + 2HCl Anion exchanger: R(OH)2 + 2HCl →RCl2 + 2H2O 9. Give the description of sand filter? The sand filter consists of a tank containing a thick top layer of fine sand followed by coarse sand, fine gravel and coarse gravel. 10. What is aeration of water? Mention its purpose?Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 40 The process of mixing water with air is known as aeration. The main purpose of aeration is (i) To remove gases like CO2, H2S and other volatile impurities causing bad taste and odour to water. (ii) To remove ferrous and manganous salts as insoluble ferric and manganic salts. 11. Explain the function of a coagulant with example? When the coagulant is added to water, it gets hydrolysed to form a gelatinous precipitate of coagulant Al (OH)3. The gelatinous precipitate, Al (OH)3, entraps the finely divided and colloidal impurities, settles to the bottom and can be removed easily. 12. Explain the function of bleaching powder as a germicide? When bleaching powder is added to water, it produces hypochlorous acid (HOCl). HOCl is a powerful germicide. CaOCl2 + H2O Ca (OH)2 + Cl2 Cl2+ H2O HOCl + HCl 13. What is meant by disinfectant? What is the advantage of using chloramines as a disinfectant? The chemicals used for destroying the harmful bacteria are known as disinfectants. Advantages: Chloramine compounds decompose slowly to give chlorine. It is a better disinfectant than chlorine. It also gives good taste to the treated water. 14. Define the term break point chlorination? (or) what is break-point chlorination? Explain: Break point chlorination is the point at which all the impurities are removed and free chlorine begins to appear. 15. What is blow-down operation? Blow-down operation is a process of removing a portion of concentrated water by fresh water frequently from the boiler during steam production. 16. What are the disadvantages of ion-exchange process: (i) Water containing turbidity, Fe and Mn cannot be treated, because turbidity reduces the output and Fe, Mn form stable compound with the resin. (ii) The equipment is costly and more expensive chemicals are needed. 17. Define desalination?Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 41 The process of removing common salt (sodium chloride) from the water is known as desalination. The water containing dissolved salts with a peculiar salty or brackish taste is called brackish water. 18. What is hardness in water? Hardness in water is that characteristic which prevents lathering of soap. This is due to the presence of certain salts of calcium, magnesium and other heavy metals dissolved. 2C17H35COONa+CaCl2→ (C17H35COO)2 +2Nacl 19. What is “hard water”? Water which does not produce lather with soap solution readily but forms a white curdy precipitate is called hard water. 2C17H35COONa +Ca+→ (C17H35COO)2 Ca +2Na+ 20. What is soft water? Water which lathers easily on making with soap solution is called soft water. 21. What is temporary hardness or carbonate hardness? It is caused by the presence of dissolved bicarbonates of calcium, magnesium and other heavy metals and the carbonate of iron. It can be removed by ( i ) Boiling the water (ii) Adding lime to the water. 22. What is permanent hardness or non-carbonate hardness? It is due to the presence of chlorides and sulphates of calcium, magnesium, iron and other heavy metals .Unlike temporary hardness, permanent hardness is not destroyed on boiling. . It can be removed by (i) Lime-soda process (ii) Zeolite process 23.What is an equivalent of CaCO3? [Mass of hardness [Chemical equivalent of producing substance] * CaCO3] Equivalents of CaCO3 = ________________________________________________ Chemical equivalents of hardness-producing substances 24. What are the units of hardness? The several types of units are given as, a) ppm--Parts per millionEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 42 It is the parts of calcium carbonate equivalents hardness per 106 parts of water, i.e., 1ppm= 1 part of CaCO3 hardness in 106 parts of water. b) Clarke’s degree I0 Clarke: 1 grain of CaCO3 equivalent hardness per gallon of water. c) Degree French It is the parts of CaCO3 equivalents hardness per 105 parts of water 1 Fr = 1 part of CaCO3 hardness equivalents per 105 parts of water 25. Define screening It is the process of removing the floating material like leaves, wood pieces etc. from water. The raw water is allowed to pass though a screen having large number of holes which retains the floating material and the water to pass. 26. Write note on aeration? The process of mixing water with air is known as aeration. The main purpose of aeration is  To remove gases like CO2, H2S and other volatile impurities causing bad taste and odour to water.  To remove ferrous and manganese salts as insoluble ferric and manganic salts. 27. Define Sedimentation. Removing suspended impurities by allowing the water to stand undisturbed for 2-6 hours in a big tank. Most of the suspended particles settle down at the bottom, due to the forces of gravity and then they are removed. 28. Write note on coagulation? Finely divided clay, silica, etc. do not settle down easily and hence cannot be removed by sedimentation. Such impurities are removed by coagulation. In this method certain chemicals called coagulants like alum, Al2(SO4)3 etc., are added to water. When the Al2(SO4)3 is added to water, it gets hydrolyzed to form a gelatinous precipitate of Al2(OH)3 entraps the finely divided and colloidal impurities settles to the bottom and can be removed easily. 29 .Define sterilization The process of destroying the harmful bacteria known as sterilization or Disinfection. The chemicals used for this purpose are called disinfectants. 30. Define sludge If the precipitate is loose and slimly it is called sludge. These are formed by the substances like MgCl2, MgCO3, MgSO4 and CaCl2. They have greater solubilities in hot water than cold water.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 43 Unit-II Polymers Polymers (derived from the Greek words, poly or many and mer means units or parts) are macro molecules formed by the combination of a large number of small molecules known as monomers. Polymers can be classified as plastics (resins), elastomers (rubber) and fibres (nylon, terylene) The properties of polymer depend on their molecular configuration, the degree of polymerization, branching and cross linking. Definition: Polymers are high molecular weight compounds whose structures are composed of a large number of simple repeating units. The repeating units are usually obtained from low molecular weight simple compounds referred to as monomers. Eg.: Polyethylene, poly vinyl chloride (PVC), poly styrene, poly butadiene, poly acrylonitrile (PAN) etc., The conversion process, monomer . Polymer , is known as polymerisation. The equations for polymerisation are represented as shown below, where ‘n’ stands a large number. Polymerisation CH2 = CH2 Repeating Units Monomer ethylene (-CH2 – CH2 – CH2 – CH2 – CH2 – CH2)n— Polyethylene ( Polymer) Polymerisation n CH2 = CH2 ----CH2 – CH2 --n Ethylene Polyethylene We know that cellulose (chief constituent of the cell walls of a plant), proteins (essential constituent of living cells), rubber, leather and natural fibres like silk, wool etc., are all polymers and these are known as natural polymers.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 44 The development of synthetic materials as substitutes for naturally occurring polymers led to the growth of polymer science. The term “ High polymers” is used to represent macro – molecules in which more than 100 monomer units are involved. Smaller combinations are referred to as dimer, trimer, tetramer etc., depending on whether the polymer molecule contains 2, 3, 4 ---etc., units of monomers. Monomer: Monomer is a micromolecule (smaller molecule) which combines with each other to form a polymer. Eg.Ethylene, vinyl chloride, styrene, butadiene, acrylonitrile etc., Polymerization Polymerisation is a process in which large number of small molecules (called monomers) combine to form a big molecule (called a polymer) with or without elimination of small molecules like H2O,CH3OH etc., Types of polymerisation: There are two types of polymerization processes: i) Addition polymerization (or) chain growth polymerization ii) Condensation polymerization (or) stepwise polymerization In addition polymerization, all atoms in the monomer are present in the polymer, but condensation polymerisation is characterized by the elimination of small molecules such as water, methyl alcohol, carbon-di-oxide etc., Addition polymers Addition polymers are formed by combination of alkene monomers to produce a single huge molecule only. Example are: (1) Polyethylene (Polythene) is an addition polymer and is obtained by polymerising ethylene, when it is heated at a pressure of 1000 atm, with a small amount of organic peroxide (eg.) (C6H5CO)2O2 --benzoyl peroxide. Polymerisation i) n CH2 = CH2 ----CH2 – CH2 ----Ethylene Polyethylene n ii) Polyvinyl chloride (PVC) It is obtained by polymerising vinyl chloride. It is carried in suspension at 520oC and 9 atm pressure. Polymerisation Cl n CH2 = CHCl ----CH2 – CH---nEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 45 vinyl chloride polyvinyl chloride iii) Polyacrylonitrile (PAN) or Orlon It is obtained by polymerising acryloritrile (vinyl cyanide). The catalyst used is a mixture of ferrous sulphate and hydrogen peroxide. Polymerisation CN n (CH2 --CHCN) --(--CH2---CH-)n---acrylonitrile polyacrylonitrile iv) Teflon (Poly tetrafluoro ethylene) (PTFE) It is obtained by polymerizing tetrafluoroethylene in aqueous suspension using ferrous sulphate and H2O as catalyst. F F n CF2 = CF2 --------C-------C---------n F F V) Polystyrene It is an addition polymer and is obtained by polymerising styrene when heated alone with or without catalyst. Polymerisation n CH = CH2 --(--CH—CH2 ---)-n Styrene Polystyrene MECHANISM OF ADDITION POLYMERISATION: The mechanism of addition polymerisation can be explained by any one of the following three types. 1. Free radical mechanism 2. Ionic mechanism 3. Co-ordination mechanism All the above mechanisms occur in three major steps namely,Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 46 1. Initiation 2. Propagation and 3. Termination FREE RADICAL MECHANISM: (i) Initiation: It is considered to involve two reactions. (a) First reaction involves production of free radicals by homolytic dissociation of an initiator (or catalyst) to yield a pair of free radicals (R·). I 2R· (Initiator) (Free Radicals) Example for commonly used thermal initiator: Thermal initiator is a substance used to produce free radicals by homolytic dissociation at high temperature. 80 -95°C C6H5COO-OOCC6H5 2 C6H5COO· (or) 2R· Benzoyl peroxide (Free Radicals) (b)Second reaction involves addition of this free radical to the first monomer to produce chain initiating species. H H R· + CH2 = C R -CH2 – C· Y Y (Free radical) ( First Monomer) (Chain Initiating species)Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 47 (ii) Propagation: It involves the growth of chain initiating species by successive addition of large number of monomers. H H H H R – CH2 -C· + n CH2 = C R – CH2 – C – CH2 -C· n Y Y Y Y Growing chain (living polymer) The growing chain of the polymer is known as living polymer.. III. Termination Termination of the growing chain of polymer may occur either by coupling reaction or disproportionation. (a) Coupling (or) Combination It involves coupling of free radical of one chain to another free radical forming a macro molecule. H H H H R—CH2—C· + · C—CH2—R R—CH2—C—C—CH2—R Y Y Y Y Macromolecule (dead polymer) (b)DisproportionationIt involves transfer of a hydrogen atom of one radical centre to another radical centre, forming two macromolecules, one saturated and another unsaturated.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 48 H H H H H H R—CH2—C· + ·C—CH2—R R—C = C + H—C—C—R Y Y Y Y H unsaturated saturated macromolecule macromolecule (dead polymers) The product of addition polymerisation is known as dead polymer. Co -polymer Co – polymers are produced by polymerizing two or more different monomers. Consider the polymersation of monomers A and B. when allowed to react separately, each gives a homopolymer. (A polymer with identical monomers). When A and B are polymerized together a co – polymer is formed. n A ( A ) n homo polymer is formed from one monomer nA + nB -(---A-----B--)n--copolymer is formed from two or more monomers Eg. 1: Cl Polymerisation Cl COOCH3 nCH2=CH + nCH2=CHCOOCH3 --(--CH2--CH—CH2—CH--)n---vinyl chloride vinyl acetate Vinyon Eg. 2: Cl Polymerisation Cl Cl nCH2=CH + nCH2=CHCl2 --(--CH2-CH—CH2—C--)n--Cl vinyl chloride vinylidene chloride SaronEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 49 Condensation polymers Condensation polymers are formed by combination of monomers with the elimination of simple molecules such as H2O, CH3OH, HCl etc., There are two main types of condensation polymers (i) polyesters and (ii) polyamides Polyesters: Eg.: Terylene (also called Dacron) is the most important polyester. It is made by heating excess ethylene glycol with dimethyl terephthalate at 2000 C in the presence of a basic catalyst. HOCH2CH2OH + CH3OOC COOCH3 Ethylene Glycol dimethyl terephthalate HOCH2-CH2-OOC COOCH3 + CH3OH Methanol Further reaction at the end --(-OCH2-CH2-OOC CO---)n— Terylene (Dacron) Polyamide Eg. Nylon 6, 6 Nylon 6,6 is the most important polyamide. It is obtained by heating adipic acid with hexamethylene diamine HOOC—(CH2)4 – COOH + HNH –(CH2)6 – NH2 Adipic acid Hexamethylene diamine Heat HOOC—(CH2)4 – CO—NH--(CH2)6 – NH2 + H2O Further reaction at each end --(-OC—(CH2)4 – CO--NH –(CH2)6 – NH---)n— Nylon 6,6 Both starting materials can be prepared from 1,3 butadiene CH2 = CH – CH = CH2Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 50 Cl2 ClCH2-CH = CH—CH2Cl NaCN NC—CH2 – CH = CH – CH2 – CN H2 /Ni NC – CH2 – CH2 – CH2 – CH2 – CN H2O /H+ Reduction HOOC – (CH2)4 – COOH H2N – (CH2)6 – NH2 Adipic acid Hexamethylene diamine In some cases, condensation polymerisation takes place without the elimination of small molecules like H2O, HCl etc., but by just opening of cyclic compounds. Differences between addition (Chain) polymerisation and condensation (step) polymerization: S. No. Addition /chain polymerisation Condensation /step polymerisation 1. The monomer must have at least one multiple bond. Examples: (i) Ethylene: CH2 = CH2 (ii) Acetylene: The monomer must have at least two identical (or) different functional groups. Examples: (i)Glycol: (ii) 6-amino hexanoic acid 2. Monomers add on to give a polymer and no other byproduct is formed. Monomers condense to give a polymer and byproducts such as H2O, CH3OH are formed. 3. Number of monomeric units decreases steadily throughout the reaction. Monomers disappear at the early stage of reaction.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 51 4. Molecular weight of the polymer is an integral multiple of molecular weight of monomer. Molecular weight of the polymer need not be an integral multiple of monomer. 5. High molecular weight polymer is formed at once. Molecular weight of the polymer rises steadily throughout the reaction. 6. Longer reaction times give higher yield, but have a little effect on molecular weight. Longer reaction times are essential to obtain high molecular weight. 7. Thermoplastics are produced. Example: Polyethylene, PVC etc., Thermosetting plastics are produced. Example: Bakelite, urea-formaldehyde 8. Homo-chain polymer is obtained. Hetero-chain polymer is obtained. Plastics Plastics are defined as polymeric materials that can be molded or extruded into desired shapes and that harden upon cooling or solvent evaporation in the presence of a catalyst. Rather than being spun into threads in which their molecules are aligned, as in fibres, plastics are cast into three dimensional forms or spread into films for packaging applications. Classification of plastics Plastics are classified in the following two ways. 1. Based on structure 2. Based on usage Classification based on structure Based on the structure and type of resin used for the manufacture of plastics, plastics are classified into two main types. 1. Thermoplastics 2. Thermosetting plastics A thermoplastic polymer is one which softens on heating and becomes rigid again on cooling. This is because there are weak attractive forces (vander walls forces) between the long polymer molecules and these are readily disrupted on heating. They are generally soluble in organic solvents. Most addition polymers and some condensation polymers are thermoplastic Eg: nylon, polythene, polystyrene etc.,Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 52 A thermosetting polymer plastic is one which becomes hard on heating. It cannot be softened by heating. Thermosetting plastics are prepared by condensation polymerization. Various polymer chains are held together by strong covalent bonds (called cross links). They are almost insoluble in organic solvents. Eg: Bakelite, polyester etc., Difference between Thermoplastic and Thermosetting resins Sl. No. Thermoplastic Resins Thermosetting Resins 1. They are formed by addition polymerisation. They are formed by condensation polymerisation. 2. They consist of linear long chain polymers. They consist of three dimensional network structure. 3. All the polymer chains are held together by weak vanderwaals forces. All the polymer chains are linked by strong covalent bonds. 4. They are weak, soft and less brittle. They are strong, hard and more brittle. 5. They soften on heating and harden on cooling. They do not soften on heating. 6. They can be remoulded. They cannot be remoulded. 7. They have low molecular weights. They have high molecular weights. 8 They are soluble in organic solvents. They are insoluble in organic solvents. Classification based on usage Based on usage plastics are classified into two types. 1. General purpose plastics 2. Engineering plastics 1.General purpose plastics (commodity) General purpose plastics have low to medium mechanical properties. They are used for the manufacture of commodity items. They account for about 80—85% of total polymer production. Examples: Polyethylene, polypropylene, polyvinyl chloride, polystyrene etc.,Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 53 Properties of General purpose plastics 1.They are mostly crystalline with low glass transition temperature(Tg) (or)they are glassy (or) amorphous polymers. 2. They have low use temperature, therefore they cannot be used at high temperature. 3. They have low to medium mechanical properties. 4. Generally they have low abrasion resistance and poor dimensional satability. Engineering Plastics Engineering plastics are a group of materials obtained from high polymer resins. They possess high mechanical strength, toughness and higher use temperature. They are mainly used in load bearing applications, generally to replace conventional materials like metal, wood, glass and ceramics. Not only engineering plastics can replace metals, but they can also be used along with metals. Characteristics (or) Properties of Engineering plastics Engineering plastics possess 1. High load bearing characteristics 2. High Mechanical strength 3. High dielectric constants 4. Readily moldable properties into complicated shapes 5. High abrasion resistance 6. Very good rigidity 7. Good dimensional stability 8. Fairly good thermal stability 9. Light weight 10. High performance properties ie., they can be used in the same manner as metals, alloys and ceramics. Applications 1. They can be used alone or in conjunction with metals, ceramics or glasses, etc., 2. They find applications in demanding areas like automobiles, defence, electrical and electronics, telecommunications, textiles, satellite, robots, computer components, etc., Important engineering plastics i) Polyvinyl chloride (PVC) Preparation:Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 54 It is obtained by polymerizing vinyl chloride. It is carried in suspension at 520C and 9 atm. pressure. Benzoyl peroxide or hydrogen peroxide is used as catalyst. Fig. : Polymerisation Cl n CH2 = CHCl ----CH2 – CH---n vinyl chloride polyvinyl chloride Vinyl chloride is prepared from acetylene by treatment with HCl in the presence of. HgCl2. HgCl2 HC CH + HCl CH2 = CH – Cl Acetylene Vinyl Chloride Properties i) PVC is colourless, odourless, non – inflammable and chemically inert powder. ii) Resistant to light, atmospheric oxygen, inorganic acids and alkalies. iii) Soluble in hot chlorinated hydrocarbons such as ethyl chloride. iv) It undergoes degradation in the presence of heat. Uses: i) It is the most widely used synthetic plastic. ii) PVC is widely used in imitation leathers, floor coverings, corrugated roofing material and gramophone record. iii) With the addition of a plasticizer, the polymer has a rubber like texture. Eg for plasticisers: butyl phthalate, dioctyl phthalate, tricresyl phosphate etc., Plasticisers are materials that are added to resins to increase their plasticity and flexibility. iv) It is used for making sheets, which are employed for tank-linings light fittings, safety helmets, refrigerator components, tyres, cycle and motor cycle mudguards. v) It is also extruded in strip and tube form for use in place of non-ferrous metals. vi) It is used in the production of pipes, cable insulations, table covers and rain-coats etc., II. Teflon or fluon (or) polytetrafluoroethylene (PTFE) Preparation PTFE is obtained by polymerisation of water– emulsion of tetrafluoro ethylene, under pressure in the presence of benzoyl peroxide as catalyst.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 55 F F F F Polymerisation n C = C C C F F F F n TFE PTFE Tetrafluoroethylene is prepared by treating chloro-difluoromethane with HCl at 9000C 2CHClF2 9000C CF2 = CF2 + 2 HCl Properties: i) Since the fluorine atoms are strongly electronegative , they tightly bond with carbon atoms in Teflon. As C--F bond is stronger, it is non – reactive and hence it is not wetted by oil and water. So teflon is non-sticky. ii) Teflon is extremely tough flexible material possessing high softening point (about 3500C) iii) It possesses extremely good electrical and mechanical properties. iv) It is chemically resistant towards all chemicals (except hot alkali metal and hot fluorine) v) It has an excellent thermal stability. Uses: (i) Teflon is familiar because of its use as non-stick coating particularly for cooking utensils. (ii) Because of its low chemical reactivity, excellent toughness, electrical and heat resistance, teflon is used as insulation for electrical items and in the manufacture of gaskets and valves. (insulating material in motors, cables, transformers, electrical fittings etc.,) (iii) It also used for making gaskets, packings, pump parts, tank linings etc., (iv) It is used for making non – lubricating bearings, chemical carrying pipes etc., (v) It is used in making non-sticking stop cocks for burettes. Polycarbonates (PC) (Lexan, merlan) Preparation: Polycarbonates are prepared by interaction of diphenyl carbonate with bisphenol – A CH3 n --–--O—C = O + n HO C OH 2 CH3Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 56 Diphenyl Carbonate Bisphenol – A Polymerisation CH3 ----O – CO – O C ----+ 2n OH n CH3 Lexane (Polycarbonate) Phenol Properties: (i) They have high impact and tensile strength over a wide range of temperature. (ii) However, they are soluble in organic solvents and alkalies. (iii) They possess good dimensional stability, stiffness, transparency etc., Uses: They are used for making electrical insulators, in electronics and electrical industries, housing apparatus, plugs, sockets, switches, sterilizable transparent containers, camera, photographic films, hair drier bodies, feeding bottles, safety windows in prison and jewelry shops etc., III. Polyurethane Preparation These polymers are prepared by reaction of aromatic isocyanate with alcohols. . n HO – (CH2)4 – OH + n OCN CH2 NCO 1,4 – butane diol toluene phenyldiisocyanate --------CONH CH2 NHCOO(CH2)4 – O ------n A PolyurethaneEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 57 If triols and di or triisocyanates are used, cross – linking can take place to give a thermosetting polymer. (1) It is obtained by the reaction of 1,4 butane diol with 1,6 hexamethylene di-isocyanate. n O=C=N—(CH2)6—N=C=O + HO—(CH2)4-OH 1,6 hexamethylene di isocyanate 1,4-butane diol n O=C=N—(CH2)6—NH—COO—(CH2)4—OH----Polymerisation -----CO – NH – (CH2)6 – NH – COO – (CH2)4 – O ----Polyurethane (Perlon – U) n Properties: i) Polyurethanes can be spun into elastic fibers such as spandex. ii) If they are formed in the presence of a low boiling liquid that will readily vapourise as the reactants are heated, a semigrid polyurethane foam results iii) More stable than polyamides. iv) Unstable in most conditions v) Possesses excellent flexibility, toughness even at sub-zero temperature vi) Excellent resistance to abrasion and solvents vii) The fibres of polyurethanes possess high stretch – resistance, high crease and wrinkle-resistance. viii) It is highly resistant to mineral and organic acids, but is less resistant to alkalies. Uses: i) Polyurethane foams are used in the construction and inter decoration of buildings. ii) Polyurethanes are also used for manufacturing of various products in the field of defence, oceanographic research and mountaineering. iii) They are used as coating, films, foams, adhesive and elastomers. iv) Modified polyurethane is used for making swim suits. v) It is mostly used for making synthetic fibers like terylene, Dacron, etc., vi) It is used for blending with wool to provide better crease and wrinkle resistance.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 58 vii) It is also used as glass reinforcing material in safety helmets, air crafts, battery boxes etc., Nylon 6,6 Preparation It is the most important polyamide. It is obtained by heating adipic acid with hexamethylene diamine. Nylon – 6,6 derives it name from its starting materials, adipic acid and hxamethylene diamine, both of which have six carbons. HOOC—(CH2)4 – COOH + HNH –(CH2)6 – NH2 Adipic acid Hexamethylene diamine Heat HOOC—(CH2)4 – CO—NH--(CH2)6 – NH2 + H2O Further reaction at each end --(-OC—(CH2)4 – CO--NH –(CH2)6 – NH---)n— Nylon 6,6 Properties: i) They are translucent, whitish horny, high melting (1600 to 2640C) polymers. ii) They possess high temperature stability and good abrasion – resistance. iii) They are insoluble in common organic solvents (like methylated spirit, benzene and acetone) and soluble in phenol and formic acid. iv) Their moldings and extrusions have good physical strength (especially high impact strength and self lubricating properties) Uses: (i) Nylon 6,6 is primarily used for fibers, which find use in making socks, dresses, carpets etc., (ii) They are also used for making filaments for ropes, bristles for tooth-brushes and films, tyre – cords etc., III. Polyethylene terephthalate (PET) or Terylene (or) polyester PreparationEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 59 One of the most important polyesters is poly (ethylene terephthalate), a polymer that is marketed under the names Dacron. Terylene and Mylar. One can obtain poly (ethylene terephthalate) by a direct acid – catalysed esterification of ethylene glycol and terephthalic acid. n HO – CH2CH2 – OH + n HO – CO CO – OH H+ /Heat --------OCH2CH2 – O--– CO CO – OCH2CH2 – O – CO CO -----n PET Properties: i) The poly (ethylene terephthalate) thus produced melts at about 2700C. ii) It can be melted, spun into fibers to produce Dacron or Terylene. iii) It can also be made into a film in which form, it is marketed as mylar. iv) The fibers possess high stretch – resistance, high – crease and wrinkle free. v) It is highly resistant to mineral and organic acids, but is less resistant to alkalies. Uses: 1) It is mostly used for making synthetic fibers like terylene (Dacron) etc. 2) It is used for blending with wool to provide better crease and wrinkle – resistance. 3) It is also used as a glass reinforcing material in safety helmets, air crafts, battery boxes etc., RUBBER Vulcanization: Both natural and synthetic rubbers are soft and tacky unless hardened by a process, called vulcanisation. Discovered in 1939 by Charles Goodyear (of subsequent tire fame) vulcanization involves heating the polymer with a few percent by weight of sulphur. The result is a much harder rubber with greatly improved resistance to wear and abrasion. In addition, fillers such as carbon black and zinc oxide are usually added to the crude rubber before vulcanization in order to remove its wearing characterstics. Vulcanization thus serves to stiffend the material by a sort of anchoring and consequently, preventing inter molecular movement of rubber springs. The extent of vulcanized rubber depends on the amount of sulphur added. For example, a tyre rubber may contain 3 to 5% sulphur, but a battery case rubber may contain as much as 30% sulphur Vulcanisation of Rubber How to improve the properties of rubber?Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 60 The properties of rubber can be improved by compounding it with some chemicals like sulphur, hydrogen sulphide, benzoyl chloride etc,, But most important addition is sulphur. Objective of vulcanization Uncross-linked rubber products, such as natural rubber obtained from latex, are soft and have poor tensile strength and abrasion resistance. To obtain a cross-linked structure of rubber,the process of vulcanization is made. Process of vulcanization The process of vulcanization consists of heating the raw rubber with sulphur to about 100—140oC. The added sulphur combines chemically at the double bonds of different long chain rubber springs. Thus the vulcanization prevents intermolecular movement of rubber springs. The extent of stiffness of vulcanized rubber depends on the amount of sulphur added. Ex: 1.Tyre rubber contains 3-5% sulphur. 2.Battery case rubber contains 30% sulphur Advantages (or) Properties of vulcanized rubber or comparison between raw and vulcanized rubberr S.NO RAW RUBBER VULCANISED RUBBER 1. Tensile strength is low (200kg/cm2) Tensile strength is high(2000kg/cm2) 2. Water absorbing tendency is high Low water absorbing tendency 3. Oxidation resistance is low Oxidation resistance is high 4. Little durability High durability 5. Low resistance to wear and tear High resistance to wear and tear 6. It has high elongation(1200%) It has moderate elongation(800%)Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 61 7. The useful temperature range is 10-60oC The useful temperature range is 40-100oC 8. It is attacked by organic solvents It is resistant to organic solvents There are two types of rubbers 1. Natural rubber 2. Synthetic rubber Natural rubber With the expansion of motor car industry, the demand for rubber increased enormously. Organic chemists found that rubber is a hydrocarbon polymer built up from the monomer isoprene.ie., (2 – methyl – 1, 3 – butadiene). Natural rubber is polyisoprene. CH3 CH3 n CH2 = C – CH = CH2 --(--CH2 – C = CH – CH2 --)n— Isoprene Polyisoprene (Natural rubber) Gutta percha is a rubber that occurs naturally as the exudate of certain tree. Synthetic Rubbers A number of different synthetic rubbers are produced commercially by diene polymersation. The synthetic rubber thus produced is quite similar to the natural rubber. a) Neoprene: It was the first synthetic rubber manufactured on a large scale. The monomer unit, chloroprene,is made from acetylene. Neoprene is particularly resistant to chemical action and is therefore used in making hoses for petrol and oil and containers for corrosive chemicals. Cu2Cl2 2CH CH CH2 = CH – C CH Acetylene NH4Cl Vinyl acetylene HCl Cl n CH2 = CH – C = CH2Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 62 ChloroprenePolymerisation Cl --(-CH2 – CH – C --CH2 --)n-Neoprene Rubber Butyl Rubber It is a co – polymer made from isobutylene and isoprene. The polymerization is carried out at 800 – 1000C in methyl chloride as solvent and with anhydrous aluminium chloride as catalyst. CH3 CH3 n CH3 – C = CH2 + n CH2 = C – CH = CH2 Isobutylene 2 – methyl – 1,3 – isobutylene (Isoprene) co-polymeristion CH3 CH3 ----CH2 – C – CH2 – C = CH – CH2 ----CH3 n Butyl rubber Butyl rubber is used for making inner tubes for tyres, motor mounts and for other vibration – damping applications. Properties: i) Butyl rubber is amorphous under normal conditions. ii) It possesses outstanding low permeability to air and other gases; less than 1/10th of natural rubber.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 63 iii) It has excellent resistance to heat, abrasion, ageing, chemicals (such as H2 SO4, HNO3, HCl and HF), polar solvents (like alcohol and acetone), but is soluble in hydrocarbon solvents like benzene. iv) It has high resistance to ozone and good electrical insulating properties. It can be vulcanized, but it cannot be hardened much, due to very low unsaturation. v) Unstabilized polyisobutylenes are degraded by light or heat to sticky low molecular weight products. Uses: (i) For making cycle and automobile tubes, automobile parts, hoses, conveyer belts, tanking-linings. (ii) It is also used for insulating high voltage wires and cables, etc., SBR (Styrene – Butadience Rubber) (also called Buna S Rubber) Preparation It is a co – polymer made from styrene and 1,3 – butadiene in emulsion at about 470C, using potassium persulphate as the initiator and an emulsifying agent (cumene hydroperoxide) n CH = CH2 + n CH2 = CH – CH = CH2 Styrene (25%) 1,3 – butadiene (75%) -------CH – CH2 – CH2 – CH = CH – CH2 ------n SBR SBR is the polymer of about 75% by weight butadiene and 25% by weight styrene. Properties: i) Styrene rubber resembles natural rubber in processing characteristics as well as quality of finished products.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 64 ii) It possesses high abrasion – resistance, high load bearing capacity and resilience. iii) It can be vulcanized in the same way as natural rubber either by sulphur or sulphur monochloride (S2Cl2) iv) It undergoes oxidation readily, when traces of ozone is present in the atmosphere. v) It requires less sulphur for vulcanization when compared to natural rubber. vi) Tensile strength and flexibility of SBR are inferior to those of natural rubber. Uses: i) Mainly used for the manufacture of motor tyres. ii) It is also used for the gasgets, foot-wear components, wire and cable insulations, carpet backing, adhesives, tank-lining etc., iii) SBR is used for making light duty tyres, belt hoses and gaskets. It is also used in foot – wear industry. COMPOSITES Composite is any material that is made out of two materials put together with a defined interface, or one material stick to in or between one or more materials. Definition Composites are combinations of two materials in which one of the materials, called the reinforcing phase, is in the form of fibres, sheets or particles and is embedded in the other materials called the matrix phase. The reinforcing material and the matrix material can be metal, ceramic or polymer. Typically reinforcing materials are strong with low densities while the matrix is usually a ductile or tough material. The composites are often more expensive than conventional polymers. Applications of composites include diesel piston, brake-shoes, pads and tyres. Materials used in polymer composites Modern composites are made of two components, a fibre and matrix. The fibre is most often glass, carbon fibre or polyethylene. The matrix is usually a thermoset like an epoxy resin, polydicyclopentadiene or a polyamide. The fibre is embedded in the matrix in order to make the matrix stronger. Fibre reinforced composites are stronger and light. They are often stronger than steel, but weigh much less. This means that composition can be used to make automobiles lighter,Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 65 and thus much more fuel efficient. Apart from the above materials additives are also added to achieve some degree of flame retardness. Fillers and pigments are also used in the process. Types of Composites Based on the type of matrix phase, composites are classified into three types. 1.Polymer matrix composites 2.Metal matrix composites 3.Ceramic matrix composites Polymer matrix Composites (or) Fibre Reinforced Polymer Composites Preparation Fibre Reinforced Plastics are produced by suitably bonding a fibre material with a resin matrix and curing them under heat and pressure. The main reinforcing agents used in FRP composites are glass, graphite, alumina, carbon, boron etc., The reinforcement material can be in different forms such as short fibres , continuous filaments or woven fabrics. The resin matrix commonly used in FRP are polyesters, epoxy, phenolic, silicone and polyamide polymer resins.The properties of FRP mainly depends on nature of the resin matrix. Characteristics(or) Properties of FRP 1. It possesses superior properties like higher yield strength, fracture strength and fatigue life. 2. Since fibre prevents slip and crack propagation, the mechanical properties of FRP gets increased. 3. It possesses high corrosion resistance and heat resistance property. Types of FRP Composites 1.Glass-FRP 2.Boron FRP 3.Carbon FRP 4.Aramid FRP 5.Alumina FRP Advantages of polymer compositionEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 66 1 They are light in weight. 2. They have high strength to weight ratio 3. They are much stronger and durable than conventional metals like steel , aluminium 4. They are most suitable for aerospace applications due to the inherent characteristic properties. 5. They have good corrosion resistance. 6. They have high temperature resistance 7. They have high fatigue strength. Uses1.Coposites of phenolic resins and nylon are used in heat shields for space crafts. 2.They are suitable for automotive and railway applications. 3 They are suitable for civil construction works. Ex: Fibre glass (mixture of styrene and polyester ), Carbon fibre( an aromatic polyamide), Kelvar (poly paraphenylene terephthalamide) ------------------------------------------------------------------------------------------------------------UNIT-II POLYMERS 2 mark question & answers 1. Define polymers and monomers? Polymers are macro molecules (giant molecules of higher molecular weight) formed by the repeated linking of large number of small molecules called monomers. Monomer is a micro molecule (small molecule) which combines with each other to form a polymer. 2. What is degree of polymerization? The number of repeating units (n) in a polymer chain is known as the degree of polymerization. It is represented by the following relationship. Molecular weight of the polymeric network Degree of Polymerisation(n) = -------------------------------------------------------Molecular weight of the repeating unit 3. Explain functionality of a monomer with suitable example? The number of bonding sites or reactive sites or functional groups present in a monomer is known as its functionality.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 67 S.No. Example Functionality 1. CH2 = CH2 (ethylene) -2 (Two bonding sites are due to the presence of one double bond in the monomer. Therefore ethylene is a bifunctional monomer). 2. H2N−(CH2)6−NH2 Hexa methylene diamine. -2 (This monomer contains two functional groups, hence it is a bifunctional monomer). 4. Explain condensation polymerization with a suitable example? It is a reaction between simple polar groups containing monomers with the formation of polymer and elimination of small molecules like H2O, HCl, etc. Example: Hexamethylene diamine and adipic acid condense to form a polymer, Nylon-6,6(Polyamide). nH2N-(CH2)6-NH2 + n HOOC – (CH2)4-COOH→ Hexamethylene diamine Adipic acid [HN-(CH2)6-NH-C-CH2-C]n-║ ║ O O Nylon-6,6(poly amide) 5. What are addition polymers? Give one example? It is a reaction that yields a polymer, which is an exact multiple of the original monomeric molecule. The original monomeric molecule, usually, contains one or more double bonds. In addition polymerization there is no elimination of any molecule. Example: Polyethylene is produced from ethylene. Heat/pressure nCH2=CH2 n…-CH2-CH2-… Ethylene Catalyst Bifunctional monomer …-(CH2-CH2)n… Polyethylene 6. What is polymerization? Polymerization is a process in which large number of small molecules (called monomers) combines to give a big molecule (called a polymer) with or without elimination of small molecules like water.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 68 7. Name the various polymerization? 1. Addition polymerization. 2. Condensation polymerization. 3. Co-polymerization 8. What are the various steps of free radical mechanism? Free radical mechanisms occur in three major steps namely. 1. Initiation 2. Propagation= 3. Termination 9. What is dead polymer? The product of addition polymerization is known as Dead polymer. 10. What is copolymerization? Give one example? It is the joint polymerization in which two (or) more different monomers combine to give a polymer. Example: Butadiene and styrene copolymerize to give GR-S rubber. Copolymerization n[CH2=CH-CH=CH2] + nCH2=CH → -(CH2-CH=CH-CH2-CH)n Butadiene Styrene ׀ GR-S rubber ׀ C6H6 C6H6 11. How is polymerization classified? Give one example? Polymerization is classified into three types 1. Addition polymerization. Example: Polyethylene is produced from ethylene 2. Condensation polymerization. Example: Nylone-6,6 is produced form hexamethylene diamine and adipic acid 3. Copolymerization. Example: GR-S rubber is produced from butadiene and styrene 12. Distinguish between addition polymerization and condensation polymerization S.No. Addition Polymerization Condensation Polymerization 1. The monomer must have atleast one multiple bond. The monomer must have at least two identical or different functional groups. 2. Monomers add on to give a polymer and no by products are formed. Monomers condense to give a polymer and by products are formed. 3. Homo-chain polymers obtained. Hetero-chain polymers obtained.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 69 13. What do you understand by disproportionation of polymer chain? Disproportionation is splitting of a polymer chain into two new compounds. Example: It involves transfer of a hydrogen atom of one radical centre from one polymer chain to another radical centre of other polymer chain, forming two macromolecules, one saturated and another unsaturated. H H H H H H H H ׀ ׀ ׀ ׀ ׀ ׀ ׀ ׀ R – C -C·-·C – C – R → R – C = C + H – C – C -R ׀ ׀ ׀ ׀ ׀ ׀ ׀ ׀ H H H H H H H H Unsaturated Saturated Macromolecule Macromolecule 14. How is nylon -6,6 formed? Bring out its important properties and uses? Preparation: It is obtained by the polymerization of adipic acid with hexamethylene diamine. nH2N-(CH2)6-NH2 + n HOOC – (CH2)4-COOH→ Hexamethylene diamine Adipic acid [HN-(CH2)6-NH-C-CH2-C-]n-║ ║ O O Nylon-6,6(poly amide) Properties: 1. It is translucent, white, horn like material. 2. It posses high temperature stability and good abrasion-resistance. Uses: It is used for fibres, which is used in making socks, dresses, carpets, etc. 15. What are plastics? Plastics are high molecular weight organic materials, which can be moulded into any desired shape by the application of heat and pressure in the presence of a catalyst. 16. What are the disadvantages of plastics?  Softness.  Embrittlement at low temperature.  Deformation under load.  Low heat-resistant and poor ductility.  Combustibility.  Polymers tend to degrade upon exposure to heat and UV-radiation. 17. List out the various ways by which polymers can be classified?Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 70 1. Classification based on structure.  Thermoplastics.  Thermosetting plastics. 2. Classification based on usage.  General purpose Plastics.  Engineering Plastics. 18. What are engineering Plastics? Engineering Plastics are a group of materials obtained from high polymer resins. They possess high mechanical strength, toughness and higher use temperature. They are mainly used in load bearing applications, generally to replace conventional materials like metal, wood, glass and ceramics. 19. What are the important applications of high performance plastics?  They can be used alone or in conjunction with metals, ceramics or glasses, etc.  They find applications in demanding areas like automobiles, defence, electrical and electronics, telecommunications, textiles, satellite robots, computer components, etc. 20. Distinguish between commodity and engineering plastics? (or) Bring out the differences of general purpose plastics and engineering plastics? S.No Commodity Engineering Plastics 1. It Possesses low abrasion resistances. It possesses high abrasion resistance 2 It possesses poor dimensional stability. It possesses good dimensional stability. 3 It possesses low mechanical properties. It possesses high mechanical strength. 4 It cannot be used at high temperature. It can be used at high temperature. 5 It is general purpose plastics. It is high performance plastics. 21. Differentiate thermoplastics and thermosetting plastics? S.No Thermoplastic resins Thermosetting resins 1 They are formed by addition polymerization. They are formed by condensation polymerization. 2 They consist of linear long chain polymers. They consist of three dimensional network structures.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 71 3 All the polymer chains are held together by weak van der waals forces. e.g. Polyethylene All the polymer chains are linked by strong covalent bonds. e.g. Bakelite 22. Mention preparation and uses of PVC? or Write any two uses of PVC? Preparation of PVC involves the following two steps. Step-I: Vinyl chloride is prepared by treating acetylene with HCl at 60-80ºC in the presence of metal chloride as catalyst.(HgCl2) CH ≡ CH + HCl → CH2 = CHCl Vinyl chloride Step-II PVC is obtained by heating water emulsion of vinyl chloride in presence of H2O2 under pressure Polymerization nCH2=CHCl -[-CH2-CH-]n-׀ Cl Vinyl chloride PVC Uses:  It is used in the production of pipes, cable insulations, table covers and rain-coats, etc.  It is also used for making sheets, which are employed for tank-linings, light fittings, refrigerator components, etc. 23. What is fluon? Mention its uses? Teflon or fluon is polytetrafluoroethane, obtained by polymerization of water-emulsion of tetrafluoroethylene in the presence of benzoyl peroxide under pressure. (CH6H5CO)2O2 nCF2 = CF2 ──────> -(-CF2-CF2-) n-Tetrafluoro ethylene Teflon Uses:  It is used as a very good electrical insulating material in motors, cables, transformers, electrical fittings.  It is also used for making gaskets, packing, pump parts, tank linings, etc.  It is also used for making non-lubricating bearings, chemical carrying pipes, etc.  It is used in making non-sticking stop cocks for burettesEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 72 24. Mention some important applications of polycarbonate? They are used for making electrical insulators, housing apparatus, plugs. sockets, switches, sterilizable transparent containers, cameras, photographic films, hair-drier bodies, baby bottles, safety windows in prison and jewelry shops, etc. 25. Give two properties and uses of perlon-U?  It possess excellent flexibility, toughness even at sub-zero temperature.  It is less stable than polymides. Uses:  Polyurethanes are used as coatings, films, foams adhesives and elastomers.  They are also used in defence, oceanographic research, mountaineering. 26. Why is Teflon behaving non-sticky? Since the fluorine atoms are the strong electronegative elements, they tightly bond with carbon atoms in Teflon. As C-F bond is stronger, it is non-reactive and hence it is not wetted by oil and water. So, Teflon is non-sticky. 26. What are elastomers? Rubbers or elastomers are non-crystalline high polymers (linear polymers), having elastic and rubber like properties. 27. What is meant by vulcanization of rubber? The process of vulcanization consists of heating the raw rubber with sulphur to about 100-140ºC. 28. Raw rubber cannot be used why?  It is plastic in nature, ie., it becomes soft at high temperature and is too brittle at low temperature.  It has poor strength.  It has large water-absorption capacity.  It is non-resistant to non-polar solvents like benzene and vegetable and mineral oils.  It is attacked by oxidizing agents like HNO3, H2SO4.  It swells and disintegrates gradually in organic solvents.  It has little durability. 29. What are the characteristics of FRP?  It possesses superior properties like higher yield strength, fracture strength and fatigue life  Since fibre prevents slip and crack propagation, the mechanical properties of FRP gets increased.  It posses high corrosion resistance and heat resistance propertyEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 73 30. How is natural rubber obtained? Natural rubber is obtained from the tree as a latex, which is a dispersion of isoprene. 31. What are composites? A composite material may be defined as, “a material system consisting a mixture of two or more micro-constituents, which are mutually insoluble, differing in form or composition and forming distinct phases”. Such a combination, possesses properties different from those of any of its constituents. 32. What are the constituents of composites? Composites consist of two important constituents.  Matrix phase.  Dispersed phase. 33. Write the characteristics of composites?  They posses higher specific strength and lower specific gravity.  They possess lower electrical conductivity and thermal expansion.  They possess better fatigue strength, corrosion and oxidation resistance.  They maintain very good strength, even up to high temperatures. 34. How are composites classified?  Metal Matrix Composites (MMC)  Ceramic Matrix Composites (CMC)  Polymer Matrix Composites (PMC) 35. What are FRPs? FRPs are fibre reinforced plastics obtained by reinforcing plastics with high strength fibre materials. 36. Explain the properties of FRP?  It possesses superior properties like higher yield strength, fracture strength and fatigue life.  Since fibre prevents slip and crack propagation, the mechanical properties of FRP gets increased.  It possesses high corrosion resistance and heat resistance property. 37. Name any two resins used as matrix forming materials in the manufacture of composites?  Polyester resin  Epoxy resin  Phenolic resin 38. Name some important FRPs?Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 74  Carbon fibre-reinforced plastics.  Glass fibre-reinforced plastics.  Aramid fibre-reinforced plastics.  Alumina fibre-reinforced plastics.  Boron fibre-reinforced plasics 39. Mention important application of FRPs?  Since FRPs are very good corrosion resistants, they are used for making acid and alkali storage tanks, cloth washing tanks, etc.  FRPs are used in mining industries for making digesters, solvent extraction tanks and filtration tanks.  FRPs are also used in making sports equipments like boots, sports cars, gold clubs, etc. 40. What is SBR? SBR is styrene-butadiene rubber consisting 75% butadiene and 25% styrene. 41. Mention some important uses of SBR? SBR is used mainly for making light duty tyres, belts, floor tiles, gaskets, gum, hoses, adhesives and electrical insulation. 42. What is GR-I rubber? It is a butyl rubber obtained by copolymerizing isobutylene with 1.5 to 4.5% isoprene in methyl chloride. 43. What are the characteristics of butyl rubber?  Butyl rubber us amorphous under normal conditions.  Unstabilized polyisobutylenes are degraded by light or heat to sticky low molecular weight products.  It has low permeability to gases.  It is soluble in hydrocarbon solvents.  It possesses good electrical insulating property and resistance to heat and abrasion. BIG QUESTION AND KEY NOTES: 1. Give the preparation, properties and uses of Teflon and Nylon-6,6  Teflon 1. Preparation 2. properties 3. Uses  Nylon-6,6 1. PreparationEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 75 2. properties 3. Uses 2. Write the free radical polymerization mechanism?  Initiation  Propagation  Termination 1. Coupling (or) Combination 2. Disproportionation 3. Discuss the synthesis and uses of SBR and Butyl rubber?  SBR1. Preparation 2. Properties 3. Uses  Butyl rubber 1. Preparation 2. properties 3. Uses 4. Give an account of fibre reinforced plastics?  Preparation  Properties  Uses 5. Describe the synthesis of polyurethane and state its uses.  Preparation  Properties  Uses 6. Explain condensation polymerization taking one example. Give any three important properties of condensation polymers?  Definition  Preparation  Properties  Uses 7. How the following polymers prepared and give any two uses of each ? 1. PVC 2. Polyurethane 3. Polycarbonate?  PVC1. Preparation 2. properties 3. Uses  Polyurethane 1. Preparation 2. PropertiesEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 76 3. Uses  Polycarbonate 1. Preparation 2. Properties 3. Uses 8. What is natural rubber? What are its drawbacks? How are they rectified through vulcanization?  Definition  Drawbacks  Rectified  Vulcanization 9. What are the advantages of polymer composites? Explain using FRP as an example?  Definition  Advantages  Example 10. Describe the synthesis of polyurethane and state its uses?  Preparation  Properties  Uses 11. Write the preparation properties and uses of PET and polyurethane?  PET1. Preparation 2. properties 3. Uses  Polyurethane 1. Preparation 2. Properties 3. Uses 12. Write Note on FRP?  Definition  Preparation  Properties  Uses 13. Distinguish between addition and condensation polymerization? 14. Define polymerization and write notes on different types of polymerization and give one preparation of each one?  Definition  Types  Preparation 15. Write the Addition polymerization mechanism?Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 77  Types  Free radical mechanism  Initiation  Example  Propagation  Termination 1. Coupling or Combination 2. Disproportionation 16. Define Plastics and write notes on advantages and disadvantages of plastics?  Definition  Preparation  Properties  Advantages  Disadvantages 17. Define Plastics and explain types of plastics and give example for each one?  Definition  Types  Preparation  Example  Properties  Uses 18. Preparation of nylons and explain properties and uses?  Preparation  Properties  Uses 19. Advantages of polymer composites (FRP)? 20. Preparation of important synthetic rubbers and explain its properties and uses?  Preparation of synthetic rubbers  Properties  UsesEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 78 UNIT – III SURFACE CHEMISTRY ADSORPTION: The presence of a higher concentration of a gas or liquid at the soild surface than in the bulk is adsorption. Adsorbent: The material providing the surface on which adsorption occurs is adsorbent. E.g., charcoal Absorption: Absorption is the process in which molecules of a substance are uniformaly distributed throughout the body of the solid or liquid. E.g., absorption of ammonia in water Adsorbate The gas or liquid that is adsorbed on the surface is called is adsorbate. Differences between adsorption and absorption: S.No. Adsorption Absorption 1 It is a surface phenomenon It is a bulk phenomenon 2 Equilibrium is attained easily Equilibrium is attained slowly 3 The concentration of molecules is Distribution is uniformEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 79 more on the surface and less in the bulk 1. Physical Adsorption (or) physisorption In physical adsorption, the adsorbed molecules are held on the surface of the adsorbent by weak physical (or) Vander Waals’s forces of attraction. Example: Adsorption of H2 (or) O2 on charcoal. 2. Chemical Adsorption (or) chemisorptions In chemical adsorption, the adsorbed molecules are held on the surface of the adsorbent by chemical bonds. Example: Adsorption of H2 on Ni Differences between Physical Adsorption (or) physisorption and Chemical Adsorption (or) chemisorptions S. NO. PHYSISORPTION CHEMISORPTION 1 It is caused by weak intermolecular Vander Waals’s forces . It is caused by strong chemical bond formation 2 Heat of adsorption is small (0-40 k.cal/mol) Heat of adsorption is large (40-400 k.cal/mol)` 3 It is reversible. It is irreversible 4 It decreases with increase in temperature. It increases with incease in temperature. 5 Multilayer adsorption takes place. Only monolayer adsorption occurs. 6 The rate of adsorption increases with the increase of pressure and concentration. The rate of adsorption decreases with increase of pressure and concentration. 7 Equilibrium is established quickly It requires timeEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 80 8 It involves very small activation energy. It involves appreciable activation energy. 9 It is not specific in nature It is highly specific. The factors that influence the adsorption of gases on solids. 1. Nature of the gas: Easily liquefiable gases (like HCl, NH3 etc.) are adsorbed more easily than the permanent gases (like H2, N2, etc.,). The higher the critical temperature (T), the more easily the gas is liquefied and consequently, more readily it is adsorbed. 2. Nature of adsorbent: The greater the surface area of the adsorbent, the greater is its absorption capacity. Larger pores on the adsorbent fecilitates large adsorption. 3. Effect of pressure: Adsorption increases with pressure of the gas 4. Effect of temperature: Since adsorption is an exothermic reaction, with an increase in temperature, the amount adsorbed (x/m) decreases, for physical adsorption. For chemical adsorption, it increases with temperature and then decreases. 5. Activation of adsorbent: In order to increase the rate of adsorption, activation is very necessary. Activation is achived as follows: Creation of rough surface: By mechanical rubbing of the solid adsorbents. Increasing effective area of the surface: By sub-dividing the solid adsorbent into finer particles. 6. Enthalpy of adsorption: Adsorption is invariably an exothermic (i.e., liberation of heat) process. In physical adsorption, the attraction between gas molecules and solid surface are due to ly weak Vander Waal’s forces. The heat of adsorption is small (about 5 k.cal/mol). In chemical adsorption, the attractive forces are due to the formation of chemical bonds. The heat of adsorption is large (about 100 k.cal/mol). 7. Reversible nature of adsorption:Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 81 Physical adsorption is a reversible process.So the adsorbed gas is easily desorbed under reverse conditions of temperature and pressure). Chemical adsorption is not a reversible process, because a surface compound is formed. 8. Thickness of adsorbed layer of gas: In physical adsorption above a certain pressure, multimolecular thick layer is formed. In chemisorptions only unimolecular thick layer is formed. Freundlich’s Adsorption Isotherm The relation between the extent of adsorption (x/m) and pressure (P) is be expressed mathematically by an empirical equation called Freundlich adsorption isotherm. (x/m)=kP1/n k=constant n=integer Derivation of Freundlich’s Adsorption isotherm The equation for Freundlich’s adsorption isotherm may be derived from geraphical results as shown below. (i) At low pressure: Adsorption increases with pressure x ∞ P (or) x = kP m m (ii) At high pressure: Adsorption is independent of pressure. x = constant (or) x = k m m (iii) At intermediate (normal) pressure: Adsorption depends on 0 to 1 power of pressure (ie., fraction power of pressure) Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 82 x α P1/n (or) x = kP1/n m m (1) where, n = integer. Equation (1) is called Freundlich’s adsorption isotherm. Taking logarithm on both sides of equation(1), Log x/m = logk + 1/n log P On ploting log x/m Vs log P, a straight line is obtained with a slope of 1/n and intercept logk Disadvantages (or) limitations of Freundlich’s adsorption isotherm 1. It is purely empirical. It has no theoretical basis. 2. It is valid only upto a certain pressure and fails at higher pressure. 3. The constants ‘k’ and ‘n’ change with temperature. 4. It fails when the concertration of adsorbate is very high. Langmuir’s Adsorption Isotherm Postulates (or) assumptions 1. Valencies of the adsorbent atoms at the surface are not fully satisfied. As a result the surface has a fixed number of adsorption sites. 2. The adsorbed gas layer is only one molecule thick 3. Each site can adsorb a single molecule. 4. Adsorption consists of two opposing processes. a. Condensation of gas molecules on the adsorbent surface. b. Evaporation of adsorbed molecules from the surface of the adsorbent. 5. After sufficient time, there is a dynamic equilibrium. The rate of condensation is equal to the rate of evaporation. 6. The surface of the solid is homogeneous, so the adsorbed layer is uniform all over the surface. 7. There is no interaction between the adsorbed molecules. 8. Adsorbed gas behaves ideally. 9. The adsorbed gas molecules do not move around the surface. Derivation of Langmuir adsorption isotherm: According to Langmuir’s assumptions, when the gas molecules strike a solid surface, some of the molecules are adsorbed and some of these are desorbed. Thereby dynamic equilibrium is established between adsorption and desorption. If A is gas molecule and M is surface then,Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 83 ka A(g) + M (surface) AM kd ,Fraction of the total surface covered =  by the adsorbed molecules Fraction of uncovered area = (1 – ) The rate of desorption is proportional Rd = kd  to number of adsorbed molecules i.,e., the covered area where kd = rate constant of desorption. The rate of adsorption is proportional } Ra = ka (1 – )P to the uncovered area ka = rate constant of adsorption At equilibrium Rate of desorption = Rate of adsorption kd = ka ( 1 -)P = kaP – ka PEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 84 kd + kaP = kaP  (kd + kaP) = kaP  = kaP (kd + kaP) (1) Dividing by kd on the right side of equat ion (1),  = (ka /kd) P 1+(ka/kd)P  = KP 1+KP (2) ka /kd = K = equilibrium constant, called adsorption coefficient. But the amount of gas adsorbed per gram of the adsorbent, x, is proportional to . x α . (3) Comparing equations, (2) and (3), x α KP 1+KP x = K1 KP 1+KP (4) Where, K1 = new constant. The equation (4) gives the relationship between the amount of gas adsorbed and the pressure of the gas at constant temperature. It is called Langmuir’s Adsorption Isotherm. The equation (4) may be written as 1+ KP = K1 KP X 1 + KP = P K1K K1K x (5) The equation (5) is similar to an equation for a straight line (ie., y = mx+c). If the graph is plotted between P/x Vs P, we get a straight line with slope K/K1K and the intercept 1/K1K This equation is found valid in all cases.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 85 Case (i) At low pressures If the pressure (P) is very low, K P is negligible compared to 1/K1K K1K i.e., 1 >> K P K1K K1K Hence equation (5) becomes 1 = P (or) x = PK1K (6) K1K x (or) x α P ie.,extent of adsorption is directly proportional to the ‘P’, at low pressures. case (ii): At high pressures If the pressure (P) is high, the term 1 is negligible. K1 K i.e., K P >> 1 K1K K1K Hence equation (5) becomes K P = P (or) x = K1 (Constant) K1K x (or) x = K1 P0 (7) i.e., adsorption is independent of pressure of the gas.The surface becomes completely covered at high pressure. Case (iii) : At normal pressures If the pressure (P) is normal (intermediate) equation (7) becomes X = K1Pn (8) Where, , n lies between 0 and 1. Equation (8) is similar to Freundlich’s adsorption isotherm.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 86 Merits and Demerits of Langmuir’s adsorption isotherm Merits; 1. Plot of P/x versus P gives a straight line only at low pressures. 2. It qualitatively explains the adsorption at various pressures. Demerits: 1. The gases do not behave ideally. 2. It fails at high temperatures. 3. Multilayer adsorption of gases is possible. 4. The adsorbent surface is not uniform throughout. 5. The adsorbent and adsorbate may chemically interact in a few cases. Applications of adsorption 1. Activated Charcoal (a) It is used in gas-masks.Activated charcoal adsorbs all poisonous gases.Purified air passes through its pores. (b) It is also used for removing colouring substances from the sugar solution and the decolouration of vinegar. 2. Silica and alumina gels They are used as adsorbents to remove moisture and for controlling humidities of room. 3. Heterogeneous catalysis Here, the reactant molecules are adsorbed on the surface of catalyst to form “adsorption complex”. Then it decomposes to give products. Example: Hydrogenation using Ni catalyst 4. Fuller’s earth It is used to refine petroleum and vegetables oils. It adsorbs unwanted materials. 5. Water softening Hard water is softened based on the principle of competing adsorption using ionexchhang resins. 6. Ore processing Sulphide ores (PbS, ZnS, Cu2S) are freed from silica and other earthly matter by froth flotation process. (oil wets sulphide ores only but not others). 7. Arsenic poisoning Colloidal ferric hydroxide adsorbs arsenic poision which is removed from the body by vomiting. 8. Test for A13+ The blue lake test for aluminium is based on the adsorption of litmus colour by A1(OH)3 precipitate. 9. DyeingEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 87 Mordant adsorbs and fixes the dyes on the cloth without attaching itself to the fabrics. 10. Creation of High Vacuum If the evacuated container is connected to a vessel of activated charcoal (or) silica gel cooled with liquid air, it will adsorb all the gas molecules in the container. This produces a very high vacuum. 11. Chromatography Selective adsorption by silica-gel, alumina etc., is used to separate pigments and also mixtures of small quantities of organic substances using adsorption chromatography. 12.Determination of surface area Surface areas of catayst powders are measured using adsorption technics.. Adsorption of solutes from solution: Solid surfaces adsorb solutes from solutions. (e.g.) Activated animal charcoal adsorbs colouring matter from sugar solution and makes the solution colorless. . 1. Positive adsorption When the solute is taken by an adsorbent, it is called positive adsorption. In this case concertration of the solution decreases after the treatment with adsorbing agent. E.g.,From a concentrated solution of KCl, charcoal adsorbs KCl only and not water. 2. Negative adsorption When the solvent is adsorbed in preference to the solute, the concentration of the solution actually increase after treatment with the adsorbing agent. This phenomenon is known as negative adsorption. From a dilute solution of KCl,charcoal adsorbs water only and not KCl Factors influencing adsorption of solutes from solutions (i) The nature of the adsorbent Some adsorbents are specifically more effective in attracting certain substances to their surface than others. Example Activated carbon is more effective in adsorbing non-electrlytes from a solution than electrolytes while inorganic solids adsorb electrolytes more readily than non-electrolytes. (ii) The area of the adsorbent An increase in the surface area of adsorbent increases the total amount of solute adsorbed. (iii) The nature of solute adsorbed The extent of adsorption is usually greater when the molecular weight of the solute is high. (iv) Effect of temperatureEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 88 An increase in temperature decreases the extent of absorption and vice versa. A rise in temperature increases the kinetic energies of solute particles and hence these particles leave the surface and thereby lowering the extent of adsorption. (v) The concertration of the solids Adsorption of solutes also involves the establishment of equilibrium between the amount adsorbed and the concentration of solute in solution. In the Freundlich adsorption isotherm, using concentration instead of pressure obeyed by adsorption from solution. x =kc1/n m where x = mass of solute adsorbed on a mass m c = equilibrium concentration of the solution K & n are constants. Log x = log (k) + 1 log c m n This implied that a plot of log x/m against log c should be a straight line.The validity of Freundlich isotherm has been tested by plotting the experimental values of log x/m Vs log c determined for adsorptions of acetic acid on charcoal at 250C. Role of Adsorbent in Catalysis (or) Adsorption Heterogeneous catalysis involves the following steps: .I:Adsorption of reactants The surface of the solid catalyst has some isolated active centres.These adsorb gaseous reactant molecules either physisorption or chemisorptions. II: Activated complex fomation The adsorbed molecules adjacent to each other combine to form an activated complex. This complex is unstable. III: Decomposition of Activated complex The activated complex breaks to form the products. The separated product molecules bind to the catalyst surface by partial chemical bonds. IV: Desorption of products The stable products are desorbed (or) released from the surface. e.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 89 Example: Hydrogenation of ethylene using Ni catalyst 1. Finely divided form of catalyst is more efficient As the fineness of the catalyst increases, the free surface area increases. Thereby active centres, responsible for the adsorption, increase. As a aresult, the activity of the catalyst is increased. 2. Rough surfaced catalyst Rough surface of a catalyst possesses “Cracks” “Peaks”, “Corners” etc. So the surface has larger number of active centres, which increase the rate of reaction. 3. Action of promoters Promoters are substances which increase the activity of a catalyst. Explanation: Promoters increase the space between catalyst and adsorbed molecules. So bonds are weakened.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 90 Promoters increase the peaks and cracks on the catalyst surface. E.g. molybdenum acts as a promoter in the hydrogenation process using nickel catalyst. 5. Catalytic poisons A substance that destroys the activity of a catalyst is a catalytic poison. Explanation: Active centres of the catalyst are decreasesd by the preferential adsorption of the poisons. So rate of reaction decreases. (e.g.) Arsenic acts as a poison for Pt catalyst. 6.Specific action of the catalyst A catalyst for one particular reaction need not catalyse another reaction. Role of Adsorbent in Ion–Exchange Process in water purification or softening. Ion-exchangers have one kind of adsorbed ion on them. They release this ion and adsorb another simlar ion. This is called ion-exchange adsorption. Definition Ion-exchange adsorption is the process of releasing one ion and adsorbing another simiar ion. Classification of ion-exchangers Ion-exchangers are classified into two types, 1. Cation exchanger. 2. Anion exchanger 1.Cation exchanger Resins with acidic functional groups (-COOH, -SO3H) exchange their H+ ions with other cations, Cation exchange resin is represented as RH2. RH2 + CaCl2 RCa + 2HClEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 91 Examples: (i) Sulphonated coals. (ii) Sulphonated polystyrene. R – SO3H ; R – COOH = RH2 2.Anion Exchanger Resins with basic functional groups (-NH2, -OH) exchange their anions with other anions. Anion exchange resin is represented as R (OH)2 R(OH)2 + H2SO4 RSO4 + 2H2O Examples: (i) Cross-linked quaternary ammonium salts. (ii) Urea-formaldehyde resin. R -NR3OH ; R-OH ; R – NH2 = R (OH)2Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 92 The hard water is first passed through a cation exchange folumn. (fig. ) It exchangess all the cations like Ca2+ , Mg2+ , Na+ etc., present in the hard water RH2 + CaCl2 RCa + 2HCl RH2 + MgSO4 RMg + H2SO4 The cation free water is then passed through an anion exchange column. It exchanges all the anions like Cl-, SO42-, HCO3-etc., present in the water. R(OH)2 + 2HCl R Cl2 +2H2O R(OH)2 + H2SO4 RSO4 + 2H2O The water coming out of the anion exchanger is completely free from all cations and anions. This water is called demineralised water or deionised water. Regeneration The cation exchange resin is regenerated by passing dilute acid RCa +2HCl RH2 + CaCl2 Similarly, the anion exchange resin is regenerated by passing dilute alkali RCl2 + 2NaOH R(OH)2 + 2NaCl Water softening (Zeolite process) Hard water contains Ca2+and Mg2+ ions. These ions form scum with soap.So hard water does not produce lather with soap. ProcessHard water is softened by passing it through a column packed with cation -exchange resin (R-Na+). The Ca2+ and Mg2+ ions in hard water are exchanged for Na+ ions. 2R-Na+ + Ca2+  R2Ca + 2Na+ Sodium Exhausted exchanger resin Regeneration The exhausted resin is regenerated by treating it with sodium ions. R2Ca + 2Na+Cl- 2R-Na+ + CaCl2Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 93 Pollution abatement of water and air In the pollution abatement of air and waste water, activated carbon is a commonly used adsorbent because of its large surface area per unit volume. Treatment of Polluted Water and Air Polluted water and air can be treated by two methods.. 1. Granular Activated Carbon (GAC) 2. Powdered Activated Carbon (PAC) 1. Granular Activated Carbon (GAC) Method A fixed – bed activated-carbon contactor is used.It can be operated singly, in series (or) in parallel. Several types of fixed-bed activated – carbon contactors are available. tant. 1. Down flow fixed-bed carbon contactors. 2. Upflow fixed-bed carbon contactors. (a) Down flow fixed-bed carbon contactors. These contain two (or) three columns operated in series (or) in parallel as shown in the fig.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 94 The water (or) air is applied to the top of the column and withdrawn at the bottom. The activated carbon is held in place with an under drain system at the bottom of the column. Advantages Adsorption of organic materials and filtration of suspended solids take place in single step. Disadvantages 1. Down flow filters need frequent back washing. 2. Plugging of carbon pores may require premature removal of the carbon for regeneration. This reduces life of the carbon. (b) Upflow fixed-bed Carbon Contactors Here the polluted water (or) air moves upwards from the base of the column as in the fig. Advantages: As the carbon adsorbs organic materials, the density of the carbon particles increases. This encourages migration of the spent carbon downwards. Disadvantages: Upflow columns have more carbon fines in the effluent, because upflow tends to expand the carbon. Bed expansion allows the fines to escape through passage created by the expanded bed. 2.Using Powdered Activated Carbon (PAC)Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 95 Here powdered activated carbon (PAC) is added directly into the effluent from the various biological treatment processes. The effluent is mixed with PAC and a coagulant (polyelectroyte) in a contact-aeration tank. After some time, the effluent is stored in a clarification tank. The carbon particles get settled at the bottom. Since the carbon particles are very fine, a coagulant such as polyelectrolyte is added to help the removal of the carbon particles. The spent carbon is regenerated by passing it through a regenerating column and is used again. Finally the water (effluent) is filtered through the filtration column. Applications of Activated Carbon 1. In odour Control: Activated carbon adsorbs odour causing molecules such as H2S. 2. As a Decolourant: Activated carbon has great surface area and pore volume. It removes colour from the solutions. 3. In Solution Purification: It removes bad tastes from water supplies, vegetable and animal fats and oils, alcoholic drinks etc., 4. In Gas Masks:Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 96 Activated carbon is used in gas masks, because of it adsorbs toxic gases. It is employed in both military and industrial gas masks. 5. In Air Conditioning It is used in air conditioning systems to control odours in auditoriums, hotels etc., 6. In solvent recovery 7. Activated carbon adsorbs most organic solvents at about 350C and releases it when heated to 1200C or above for solvent recovery. 8. In Cigarette Filters Activated carbon is impregnated in cigarettes to filter carbon and nicotine particles. Surface Chemistry PART-A 2 mark question & answers 1. Define adsorption and adsorbate Adsorption: The phenomenon of a higher concentration of molecules of a gas or liquid at a solid surface than in the bulk is called adsorption. The adsorption of a gas on a solid is sometimes called occlusion. Adsorbate: The substance which is held on the surface of the solid is called adsorbate 2. What is sorption? Sorption is the process in which both adsorption and absorption takes place simultaneously 3. Define the terms adsorbent and adsorbate giving suitable examples Adsorbate: The substance which is held on the surface of the solid is called adsorbate Example: H2 gas Adsorbent: The solid that takes up a gas or a solute from the solution is called the adsorbent. Example: Ni (Solid) 4. What is chemisorption? Give an exampleEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 97 Chemical adsorption is the one, in which the adsorbed molecules are held on the surface of the adsorbent by chemical bonds (Covalent bond or ionic bond) Example: Adsorption of H2 on Ni 5. What is physical adsorption or physisorption.Give an example? Physical adsorption or physisorption is the one, in which the adsorbed molecules are held on the surface of the adsorbent by weak physical or van der Waals process. Example: Adsorption of H2 or O2 on charcoal 6 .Mention some important characteristics of adsorption  Adsorption on surface of a solid is always spontaneous  Adsorption is always accompanied by evolution of heat  Adsorption is accompanied both by decrease in enthalpy and entropy of the system  Adsorption is a selective process 7. Explain the effects of temperature on adsorption Physical adsorption: It occurs rapidly at lower temperature and decreases with increase in temperature Chemical adsorption: It increases with increase of temperature and then decreases 8. What are the differences between absorption and adsorption? S.No Adsorption Absorption 1 Adsorption is a surface phenomenon Absorption is a bulk phenomenon 2 It is a rapid process It is a slow process 3 Equilibrium is attained easily Equilibrium is attained slowly 4 The concentration of the molecules are more on the surface and less in the bulk But, distribution is uniform 9. How does chemisorption differ from physisorption (or)Write any two differences between chemisorption and physisorption S.No Physisorption ChemisorptionEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 98 1 It is caused by intermolecular Vander wall’s forces(Weak) It is caused by chemical bond formation(Strong) 2 Heat of adsorption is low(20-40 k.cal/mol) Heat of adsorption is high (40-400 k.cal/mol 3 Adsorption is completely reversible Adsorption is completely Irreversible 4 Multilayer adsorption occurs Only monolayer adsorption occurs 5 Adsorption decreases with increase in temperature Adsorption increases with temperature 10. How will you increase the activity of an adsorbent? Activation leads to increase in the surface area of the adsorbent, which increases adsorption. Activation is achieved by the following ways i) Creation of rough surface  By mechanical rubbing of the solid adsorbents  By subjecting to some chemical reactions on the solid adsorbent. ii) Increasing effective area of the surface  By sub-dividing the solid adsorbent into finer particles  By heating of solid adsorbent in superheated steam, now its pores are opened and adsorption increases 11. Explain the function of activated charcoal with example  It adsorbs coloring matter present in sugar solution  It also adsorbs out NH3 from the solution of NH4OH and phenolphthalein  It also adsorbs certain acids like CH3COOHand (COOH)2 present in water, thereby acid concentration in water decreases 12. Define adsorption? What is an adsorption isotherm? Adsorption: The phenomenon of concentration of molecules of a gas or liquid at a solid surface is called adsorption. Adsorption isotherm: Adsorption isotherm is a relationship between magnitudes of adsorption with pressure. X/m =KP1/n 13.What is Freundlich’s adsorption isotherm? The relationship between the magnitude of adsorption (X/m) and pressure (P) can be expressed mathematically by an equation known as Freundlich’s adsorption isotherm. X/m =KP1/n 14. Write a suitable equation commonly applied to the adsorption of liquids on Solids. X/m =KC1/nEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 99 log X/m = log K + 1/n log C Where, K & n = Constants X= mass of adsorbate m= mass of adsorbent 15. Explain the limitations of freundlich’s adsorption isotherm? Freundlich equation is purely empirical and has no theoretical basis The equation is valid only up to a certain pressure and invalid at high pressure. The constants K and n are not temperature independents, they vary with temperature Freundlich’s adsorption isotherm fails, when the concentration of adsorbate is very high 16.What is Langmuir’s adsorption isotherm? How it is mathematically represented? The relationship between the amounts of gas adsorbed to the pressure of the gas at constant temperature is known as Langmuir’s adsorption isotherm. It is represented mathematically as X = K’ KP/1+ KP 17. What is a demerit of Langmuir’s adsorption isotherm? Langmuir’s adsorption isotherm holds good at lower pressure but fails at higher pressure. 18.What are promoters? Promoters are defined as, the substances which increase the activity of a catalyst. 19. What is catalytic poisoning? A substance which destroys the activity of the catalyst is called catalytic poisoning. 20.What is the effect of temperature and pressure on the adsorption of hydrogen gas on charcoal ? Adsorption of hydrogen gas on charcoal is rapid at lower temperature and decrease with increase in temperature, but the rate of adsorption increases with increase of pressure. 21.What is the effect of increase in temperature and increase in pressure on the adsorption of gas on a solid? Effect of increase in pressure:  Adsorption generally increases with increase of pressure Effect of increase in temperature:  Physical adsorption: It increases with increase in temperature  Chemical adsorption: It increases with increase in temperature and then decreases 22. How is arsenic poisoning removed from the body?Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 100 Colloidal ferric hydroxide is administered, which adsorbs arsenic poison and is removed from the body by vomiting 23. Define ion-exchange adsorption (or) what do you understand by ion-exchange adsorption. Give one example Ion-exchange adsorption is the process of releasing the ion and adsorbing another like ion. Example: Water softening using zeolite When water containing Ca2+ and Mg2+ ions are allowed to pass over a zeolite bed, Ca2+ and Mg2+ ions are replaced by Na+ ions. 2R-Na+ +Ca2+ R2Ca +2 Na+ 24. How is evaporation of water in lake minimized? Due to scarcity of water during summer layers of stearic acid is spread over water lakes and reservoirs. The adsorbed stearic acid on the surface of water minimizes evaporation of water 25.What is the role of adsorbent in catalysis?  The catalyst (adsorbent) adsorbs the reactant molecules on its surface and brings them in close proximity for the reaction to occur.  It helps in the formation of activated complex,  Reactants are easily broken and the products are easily formed. 26.Where is ion exchange adsorption applied? Ion exchange adsorption is applied, where the dissolved ions are exchanged with the ions of the adsorbents. Example:In water softening Ca2+,Mg2+,SO42-ions are removed by ion exchange resin. R-Ca + 2 HCl RH2 + CaCl2 R-SO4 + 2NaOH R (OH)2 + Na2SO4 27. Define i) Elution ii) Eluent The process of recovery of various substances from the chromatogram is known as elution. The solvent used for this purpose is called eluent 28. List out the important applications of chromatography?  Chromatography is used to identify the products  Purify the substance from their contaminants  Concentration of solutes from solutions 29. What is activated carbon? Activated carbon is a form of carbon that is processed to make it extremely porous and this have a very large surface area.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 101 30.What is the use of activated carbon? It is used to filter the harmful chemicals from the polluted air &water 31.What are the merits of activated carbon treatment of water?  Activated carbon treatment of water filters a wide range of chemicals like fuels, dioxin PCB’s and radioactive wastes  It can also remove some types of metals, if present in small amounts 32.What are the demerits of activated carbon treatment of water?  Activated carbon treatment does not destroy the chemicals  Activated carbon treatment does not bind well to certain chemicals including alcohols, glycols, ammonia, strong acid and bases PART-B 1. Explain the classification and functions of ion-exchangers  Cation exchanger  Anion exchanger 2. Define the term adsorption and list its application  Activated charcoal  Silica and alumina gels  In heterogeneous catalysis  Fuller’s earth  Ion-exchange resin  Froth flotation process  Arsenic poisoning  Lake test for Al 3+  Mordants  Production of high vaccua 3. Explain the role of adsorption in demineralization of water  Cation exchanger  Anion exchanger  Demineralization process  Zeolite process  Electrical demineralization processEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 102 4. Derive freundlich’s adsorption isotherm. Give the condition in which it fails 5. Derive an expression for Langmuir’s adsorption isotherm. Show that at normal pressure Langmuir’s adsorption isotherm becomes identical with freundlich’s adsorption isotherm 6. Explain the role of adsorbents in pollution abatement 7. Explain the role of adsorption in catalysis. Give examples  Finely divided state of catalyst is more efficient  Activity of a rough surfaced catalyst  Action of promoters  Action of catalytic poison  Specific action of the catalyst  Action of heterogeneous catalysis 8. Distinguish between physisorption and chemisorption 9. What are the factors that influence the adsorption of gases on solids? Discuss in details  Nature of gases  Nature and surface area of adsorbent  Heat or Enthalpy of adsorption  Reversible character of adsorbed gases  Effect of pressure of gas  Effect of temperature of gas  Thickness of adsorbed layer of gas  Activation of adsorbent 10. Explain the role of activated carbon in pollution abatement? Treatment of polluted water and air Using granular activated carbon (GAC) i) Down flow fixed-bed carbon contactors ii) Up flow fixed-bed carbon contactors b) Using powdered activated carbon (PAC) 11. Write the applications of activated carbon?  In odour control  As a decolourant  In solution purification  In gas masks  In air conditioningEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 103  In industrial recovery  In cigarette filters 12. What are the factors that influence the adsorption of solutes from solutions? Discuss in detail  Effect of temperature and concentration i) Negative adsorption ii) Positive adsorption  Effect of surface area  The nature of the solute adsorbedEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 104 UNIT -IV Non -conventional Energy Sources and Storage Devices The common sources of power generation are coal, petroleum products, hydroelectricity etc. These are called conventional sources of energy. Conventional energy sources will last only for a few decades. So we look for other sources of power generation like nuclear fuels, solar cells, wind energy etc. These sources are called non-conventional energy sources. Nuclear Fission Nuclear fission is the process of splitting a heavy nucleus (by bombarding it with projectiles) into two approximately equal lighter nuclei. Simultaneously huge amount of energy is released (e.g) 235 1 236 93 1 92 0 92 36 0 U n U Kr 3 n energy          +140 Ba56 During nuclear fission, there is a loss in mass which is converted into energy as per Einstein’s mass energy equation E=mc2 m = Loss in mass c= Velocity of light. Nuclear Fusion Nuclear fusion is the process of combination of lighter nuclei into heavier nucleus with simultaneous release of huge amount of energy. (e.g) 2 2 4 1 1 2 H H He energy    In this reaction 0.026 amu mass is lost which is converted into energy. Note: To combine two positively charged nuclei, we have to overcome nucleus -nucleus repulsive forces. A temperature of 106 Kelvin is required. Differences between nuclear fission and fusion S.No. Nuclear fission Nuclear fusion 1. It is the process of breaking a heavier nucleus into lighter nuclei It is the process of combination of lighter nuclei into a heavier nucleus 2. Radioactive rays are emitted. Radioactive rays are not emitted. 3. It occurs at ordinary temperatures. It occurs at high temperatures. (>106K)Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 105 4. The mass number and atomic number of new elements are lower than that of parent nucleus. The mass number and atomic number of product is higher than that of starting elements. 5. It leads to a chain reaction It does not lead to chain reaction. 6. It emits neutrons It emits positrons 7. It can be controlled to produce power. It cannot be controlled Nuclear chain Reaction When 235 92U undergoes fission, two to three neutrons are produced. Some of these neutrons attack 235 92U , and further fission of nucleus occurs. This process repeats as a chain, leading to nuclear chain reaction. Nuclear Reactor A nuclear reactor is a device to conduct nuclear fission at a controlled rate so that the liberated energy is used to generate power. Components of a light water nuclear reactor and its working for power generation Components The components of nuclear reactor are: (1) Reactor core (2) Reflector (3) Pressure vessel (4) Shielding (5) Heat exchanger (6) Turbine. 1.Reactor core: It contains fuel, moderator, coolant and control rods. Fuel is generally enriched uranium-235 in the form of rods. Pu-239 can also be used. Moderators: They reduce the kinetic energy of the neutrons produced during fission and slow their speed. Graphite, beryllium and heavy water are good moderators. Coolants: Coolants remove the immense heat produced in the reactor and bring it for use. Ordinary water, heavy water and liquid sodium are coolants. Control rods: To control fission rate, movable cadmium or boron control rods are suspended between fuel rods. These control rods can be raised or lowered to absorb excess neutrons and control fission rate. 2) Reflector :Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 106 Reflectors are placed around reactor core. They reflect back neutrons that leak out from the surface of the core. Graphite, heavy water are good reflectors. 3) Pressure vessel: It encloses the core and reflector. It provides entrance and exit for coolant. It can withstand high pressures. There are holes at the top to insert or pull control rods. 4) Shielding: To prevent  and  rays and neutrons coming out from the reactor, a steel covering is used close to the reactor core. Further a thick layer of concrete surrounds the steel cover. 5) Heat exchanger: It transfers heat from the reactor to boil water and generate steam. Heat exchanger contains sea water, which is converted into steam. 6) Turbines: Steam from heat exchanger operates a steam turbine which drives a generator to produce electricity. Working: The Control rods (10B) are inserted between fuel rods and fission is triggered. Controlled fission occurs. The heat emitted is absorbed by coolant (light water). The heated coolant (at 300oC) goes to heat exchanger containing sea water. Coolant transfers heat to sea water. Sea water is converted into steam, which drives turbines to produce electricity. Mass defect: The difference between the masses of reactants and products in a nuclear reaction is called mass defect. Fissile Nuclei: Nucleus like uranium-235 which is directly used for fission is called fissile nuclei. Fertile nuclei 238U and 232Th are not used directly for fission. But they can be converted into fissile nuclei. 238U and 232Th are called fertile nuclei.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 107 238 1 239 92 0 94 U n Pu 2e Fertile Fissile     Breeder reactor A nuclear reactor with conversion or mutilplication factor greater than one is a breeder reactor. A breeder reactor generates fissionable nuclei from fertile nuclei. E.g., the fertile material like uranium-238 is converted into fissile 239 94 Pu by using slow neutorns. 239 94 Pu undergoes fission and produces energy. Working : `In breeder reactor, 235 92U is used as trigger to produce sufficient neutrons. These are used to convert 238 92U to 239 94 Pu . Plutonium undergoes fission with the production of three neutrons. One neutron is used to propagate fission chain. The other two neutrons react with 238 92U to produce 239 94 Pu . Thus breeder reactor produces two 239 Pu atoms for each 239 Pu consumed. Thus more fissionable material is produced than consumed. Hence the reactor is called breeder reactor. Critical Mass: The minimum amount of fissile material (U235) required to continue the nuclear chain reaction is called critical mass. Solar Energy Conversion Solar energy conversion is the conversion of direct sunlight into useful forms of energy like electricity, heat etc. It takes place by two mechanisms namely thermal conversion and photoconversion. Solar Cell or Photovoltaic cell Solar cell converts sun light directly into electrical energy. Principle: The principle of Solar cell is based on photovoltaic effect. When light radiation falls on the p-n junction semi conductor device, charge separation takes place and a potential difference is set up. This causes flow of electrons and produces electricity.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 108 Working: When sun rays fall on the top layer of p-type semiconductor, electrons from valence band are promoted to conductance band and cross the p-n junction into the n-type semiconductor. A potential difference is set up between the two layers. This causes flow of electrons and produces electricity. When the ‘p’ and ‘n’ layers are connected to an external circuit, electrons flow from ‘n’ layer to ‘p’ layer and current is generated. Application of Solar Cell 1. Lighting purpose Now a days electrical street lights are substituted by solar street lights. 2. Solar pumps are run by solar battery A large number of solar cells are connected in series to form a solar battery. Solar battery produces enough electricity to run water pump, etc., They are also used in remote areas where conventional electricity is not available.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 109 3. Solar cells are used in calculators, electronic watches etc. 4. Solar cells are superior to other type of cells, because they are non-polluting and eco-friendly. 5. Solar cells are used to drive vehicles. 6. Silicon solar cells are used as a source of electricity in space crafts and satellites. Advantages of Solar cells 1. Solar cells are used in remote areas, forests and hilly regions. 2. Maintenance cost is minimum. 3. Solar cells are pollution free. 4. They have long life. Disadvantages 1. Solar cells are costly. 2. Storage of energy is not possible with solar cells. Wind Energy The force of high speed wind is used to rotate blades of wind mills. The rotational motion of blades drives machines like water pump, flour mill and electric generators. Thus the force of wind is harnessed to produce useful forms of energy. This is wind energy. Generation of electricity from wind mill Wind energy is used to generate electricity with the help of wind mills. The crank of the wind mill is connected to a dynamo. When the blades of wind mill rotate, they turn the coil of the dynamo and produce electricity. Usually a number of wind mills are erected side-by-side. The outputs from the wind mills are coupled to generate electricity for commercial purpose. This type of system is wind energy farms. Condition: Wind speed should be more than 15km/hr.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 110 Advantages of wind energy (i) It is cheap and economical. (ii) It is renewable (iii) It does not cause pollution. Disadvantages (i) They produce noise. (ii) Wind farms erected on the migratory routes of birds create problems. (iii) Wind turbines interfere with electromagnetic signals. Fuel Cells Definition Fuel cell is a voltaic cell. It converts chemical energy of the fuels directly into electricity without combustion. In these cells, the reactants and electrolytes are continuously supplied to the cell. Fuel + Oxygen  Oxidation products + Electricity. Examples : Hydrogen -oxygen fuel cell. Hydrogen -oxygen fuel cell Itl is the simplest and most successful fuel cell. The fuel-hydrogen and the oxidiser-oxygen and the liquid electrolyte are continuously supplied to the cell. Description The cell has two porous electrodes, anode and cathode. The electrodes are made of compressed carbon containing a small amount of catalyst (Pt, Pd, Ag). Between the two electrodes an electrolytic solution, 25% KOH is filled. Working Hydrogen passes through the anode compartment, where it is oxidised. Oxygen passes through the cathode compartment, where it is reduced.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 111 Cell reactions 2H2+4OH- 4H2O At anode: +4e-O2 +2H2O + 4e- At cathode: 4OHOveeral cell reaction: 2H2+O2  2H2O emf of the cell = 0.8 to 1.0V Advantages of Fuel Cells 1. They are efficient and instant in operation. 2. They are pollution free. 3. They produce electric current directly from the reaction of a fuel and an oxidiser. 4. They are light in weight Disadvantages 1. Fuel cells cannot store electric energy. 2. Electrodes are expensive and short lived. 3. H2 should be pure. Applications 1. H2 -O2 fuel cells are used in space crafts, submarines to get electricity 2. In H2 -O2 fuel cell, the produt water is a valuable source of fresh water for astronauts. Types of Battery 1. Primary Battery (or) Primary cell In this cell, the electrode reactions cannot be reversed by passing an external electric current. Cell reaction occurs only once. After use, they become dead. They are not chargeable. Examples: Dry cell 2. Secondary Battery (or) Secondary cellEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 112 In this cell, the electrode reactions are reversed by passing an external electric current. So they are rechargable by passing electricity and used again and again. They are also called Storage cells (or) Accumulators. Examples: Lead acid storage cell, Nickel-cadmium cell. Alkaline Battery This is an improved form of dry cell.The electrolyte NH4C1 is replaced by KOH. Alkaline battery has a zinc cylinder filled with an electrolyte containing powdered Zn, KOH and MnO2 in the form of paste. A carbon rod (cathode) is immersed in the electrolyte at the centre of the cell. The outer cylindrical zinc body is anode. Cell Reactions At anode: Zn(s) + 2OH-(aq)  Zn(OH)2(s)+2e-At cathode : 2MnO2(s) + H2O(l)+ 2e- Mn2O3(s) + 2OH-(aq) Overall Cell Reaction Zn(s) + 2MnO2(s) + H2O(1)  Zn(OH)2(s) + Mn2O3(s) In the cathode, Mn is reduced from +4 oxidation state to +3 state. emf of the cell is 1.5 V. Advantages of alkaline battery over dry battery (i) Zinc does not dissolve readily in alkaline medium. (ii) Alkaline battery has a longer life than dry battery, because there is no corrosion of Zn. (iii) It maintains its voltage, when the current is drawn from it. Uses Used in calculators, watches etc. Lead Storage cell or Lead Accumulator or Acid Storage CellEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 113 A lead storage cell is a secondary battery.It can operate as a voltaic cell as well as an electrolytic cell.When it acts as a voltaic cell, it supplies electrical energy . During charging it operates as an electrolytic cell. Description A lead storage battery has a number of voltaic cells connected in series. The anode is lead plates. The cathode is PbO2 plates. The lead plates (anodes) are connected in parallel and PbO2 plates (cathodes) are also connected in parallel. The plates are separated from the adjacent ones by insulators like rubber or glass fibre. The entire set up is immersed in dil. H2SO4 (38% by weight) having a density of 1.30 g/cc. The cell is represented as; Pb PbSO4 H2SO4(aq) PbO2 Pb Working (Discharging) When current is drawn the cell, the following reaction occurs. At anode: Lead is oxidized to Pb2+ ions. They combine with 24 SO  to form insoluble PbSO4. At cathode: PbO2 is reduced to Pb2+ ions. They combine with 24 SO  forms insoluble PbSO4. discharging charging 2 2(s) 4 PbO 4H SO 2e       4(s) 2 PbSO 2H O  Overall cell reaction during use (discharging): discharging charging (s) 2(s) 2 4 (aq) Pb PbO 2H SO   4 2 2PbSO 2H O Energy   PbSO4 is precipitated at both the electrodes during the cell reaction and H2SO4 is used up. So the concentration of H2SO4 decreases. Its density falls below 1.3g/cc. So the battery needs recharging.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 114 Recharging the Battery The cell is charged by passing electric current in the opposite direction. The electrode reactions are reversed. Pb is deposited at the anode and PbO2 at the cathode. The density of H2SO4 also increases. The reaction during charging is Advantages (i) Construction is easy. (ii) It gives high current. (iii) The self-discharging rate is low. (iv) It acts effectively even at low temperatures. Disadvantages (i) Recycling of the battery produces environmental pollution. (ii) Mechanical strain and normal bumping decreases battery capacity. Uses1. Used to supply electric current in automobiles like cars, buses, etc., 2. It is used in gas engine ignition, telephone exchanges, hospitals etc., Nickel -Cadmium Cell (or) Nicad Battery Description Nickel-cadmium cell has a cadmium anode and a metal grid containing a paste of NiO(OH)(s) acting as a cathode. The electrolyte is KOH. It is represents as: Cd Cd(OH)2 KOH(aq) NiO(OH)(s) Ni Working (Discharging) At anode: Cadmium is oxidised to Cd2+ and it combines with OH-ions to form insoluble Cd(OH)2. discharging charging (s) Cd 2OH  2(s) Cd(OH) 2e  At Cathode: NiO(OH) is reduced to Ni2+ ions.Theycombine with OH-ions to form Ni(OH)2.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 115 discharging charging (s) 2 2NiO(OH) 2H O 2e   2(s) 2Ni(OH) 2OH  Overall reaction: discharging charging (s) 2 Cd 2NiO(OH) 2H O   2(s) 2(s) Cd(OH) 2Ni(OH) Energy   Recharging the Battery When a current is passed in the opposite direction, the cell reaction gets reversed. Cd gets deposited at anode and NiO(OH) at the cathode. The reaction during charging is Advantage1. It is small and light in weight. 2. It has longer life than lead acid storage cell. 3. Like the dry cell, it is packed in a sealed container. Disadvantage It is more expensive than lead storage battery. Uses Used in calculators, electronic flash units, transistors, cordless appliances etc., Lithium Battery It is a solid state battery. Solid electrolyte is used. Construction It has a lithium anode and a TiS2 cathode. A solid electrolyte, a polymer, is packed in between the electrodes. The polymer electrolyte permits the passage of ions but not that of electrons. Working (Discharging)Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 116 The anode is connected to cathode through the polymer electrolyte. Lithium ions and electrons are produced at the anode . The cathode receives the lithium ions and electrons. At anode: Li(s)  Li+ + e-At Cathode: TiS2(s) + e- TiS2-Overall reaction: Li(s) + TiS2(s)  Li+ + TiS2- LiTiS2 Recharging The battery is recharged by passing an external current, which drives the lithium ions back to the anode. The overall reaction is LiTiS2 Li+ + TiS2-This cell has a voltage of 3.oV. Uses: It possesses very small size and high energy density. So it is used in calcutors, electronic flash units, computers, transistors head phones etc. Advantages (i) The cell has a voltage of 3.0V. (ii) Li is a light-weight metal. Just 7g (1 mole) of Li is required to produce 1 mole of electrons. (iii) Li has the most negative Eo value. So it gives a higher voltage than other cells. (iv) It is a total solid state battery. There is no risk of current leakage from the battery. (v) It is manufactured in a variety of sizes and shapes. Disadvantages It is more expensive than other batteries. UNIT-IV NON-CONVENTIONAL ENERGY SOURCES Two marks: 1. Define nuclear fission. Give an example: Nuclear fission is defined as “the process of splitting of heavier nucleus into two (or) more smaller nuclei with simultaneous liberation of large amount of energy”. 2. Mention a few important characteristics of nuclear fission. a. A heavy nucleus (U235 (or) Pu239), when bombarded by slow moving neutrons, splits into two or more nuclei. b. Two or more neutrons are produced by fission of each nucleus. c. Large quantities of energy are produced as a result of conversion of small mass of nucleus into energy.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 117 3. What is nuclear fusion? Give an example: “The process of combination of lighter nuclei into heavier nuclei, with simultaneous liberation of large amount of energy”. Nuclear fusion occurs in sun. Example: 1H2 + 1H2 -------> 2He4 + energy 4. What is nuclear chain reaction? A fission reaction, where the neutrons from the previous step continue to propagate and repeat the reaction,is called nuclear chain reaction. 5. Given any two differences between nuclear fission and fusion? 6. What is super critical mass and sub-critical mass of U235? (a) Super critical mass If the mass of the fissionable material (U235) is more than the critical mass, it is called super critical mass. (b) Sub-critical mass If the mass of the fissionable material is smaller than the critical mass, it is called sub-critical mass. 7. What is nuclear energy? Explain using a suitable example: The energy released during the nuclear fission is called nuclear fission energy (or) nuclear energy. Example: When U235 nucleus is hit by a thermal neutron, the following reaction occurs with the release of energy. 92U235 + 0n1------->56Ba139 + 36Kr94 + 3n01+ Energy 8. Give any one nuclear fission reaction; mention the factors that impede the nuclear chain reaction. S.No Nuclear fission Nuclear fusion 1. It is the process of breaking a heavier nucleus. It is the process of combination of lighter nuclei. 2. It emits radioactive rays. It does not emit any kind of radioactive rays. 3. It occurs at ordinary temperature It occurs at high temperature (> 106 K)Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 118 92U235 + 0n1-------> [92U236] -------> 56Ba140 + 36Kr93 + 3n01 The factors that impede the nuclear chain reactions are:  Some of the neutrons may escape from the surface to the surroundings.  Some of the neutrons may be absorbed by 92U235 present as impurity. 9. Write any one nuclear fusion and fission reaction. (a) Nuclear fusion reaction 1H2 + 1H2 -------> 2He4 + Energy (b) Nuclear fission reaction 92U235 + 0n1------->[92U236] -------> 56Ba140 + 36Kr93 + 3n01 + ENERGY 10.What are the types of nuclear fission reaction? The nuclear fission reactions are of two types: (a). Uncontrolled fission reactions – Atom bomb. (b). Controlled fission reactions – Nuclear reactor. 11.What is a nuclear reactor? The arrangement or equipment used to carry out fission reaction under controlled conditions is called a nuclear reactor. 12.What is light water nuclear-power plant? Light-water nuclear-power plant is the one, in which U235 fuel rods are submerged in water. Here the water acts as coolant and moderator. 13.What are moderators? Give some example: The substances used to slow down the neutrons are called moderators. Examples:Ordinary water, Heavy water, Graphite, Beryllium. 14.What is the major role of pressure vessel in the nuclear reactor? It withstands the pressure as high as 200 kg/cm2.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 119 15. What are fissile nucleides and fertile nucleides? (i) The directly fissionable nucleides such as U235 & Pu 239 are called fissile nucleides. (ii) The non-fissionable nucleides such as U238& Th232 are called fertile nucleides.They can be converted into fissionable nuclei. 92 U238 + 0 n1  94 Pu239 + 2e-16. Mention any two differences between a nuclear reaction and a chemical reaction. S.No. Nuclear reaction Chemical reaction 1. Rapid exothermic reaction. Slow reaction. 2. Initiated by neutrons. Initiated by heat or cold. 17. What are the general components of a nuclear reactor? a. Fuel rods b. Control rods c. Coolants d. Moderators e. Pressure vessel f. Protective shield g. Turbine 18. What is Breeder reactor? Breeder reactor is the one which converts non-fissionable material (U238, Th232) into fissionable material (U235, Th239). 92 U238 + 0 n1  94 Pu239 + 2e-19. What is meant by solar energy conversion. How is it done? Solar energy conversion is the process of conversion of direct sunlight into more useful forms. This solar energy conversion occurs by the following two mechanisms. a. Thermal conversion b. Photo conversion 20. What is thermal conversion? Thermal conversion involves absorption of thermal energy in the form of IR radiation. Solar energy is an important source for low-temperature heat (temperature below 100oC), which is useful for heating buildings, water and refrigeration.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 120 21. Define photo conversion? Photo conversion involves conversion of light energy directly into electrical energy. 22. What is photogalvanic cell (or) Solar cell? Photogalvanic cell is the one, which converts the solar energy (energy obtained from the sun) directly into electrical energy. It consists of a p-type semiconductor (such as Si doped with B) and n-type semiconductor (such as Si doped with P). They are in close contact with each other. 23. Explain the applications of solar cells. 1. Solar cells are used in calculators, electronic, watches, radios and TVs. 2. Solar cells are superior to other type of cells, because these are non-polluting and eco-friendly. 3. Solar energy can be stored in Ni-Cd batteries and lead-acid batteries. 4. Solar cells can be used to drive vehicles. 5. Solar cells, made of silicon, are used as a source of electricity in space craft and satellites. 24. What are fuel cells? Fuel cell is a voltaic cell, which converts the chemical energy of the fuels directly into electricity without combustion. In these cells, the reactants, products and electrolytes pass through the cell. Fuel + Oxygen -------> Oxidation products + Electricity. 25. What are the electrodes used in the fuel cells? Compressed carbon containing a small amount of catalyst like Pt, Pd, Ag are used in the fuel cells 26. What are the applications of H2-O2 fuel cells? a. H2-O2 fuel cells are used as auxiliary energy source in space vehicles, submarines or other military-vehicles. b. In case of H2-O2 fuel cells, the product of water is proved to be a valuable source of fresh water by the astronauts. 27. What is wind energy. How is it obtained? Moving air is called wind. Energy recovered from the force of the wind is called wind energy. The energy possessed by wind is because of its high speed. The wind energy is harnessed by making use of wind mills.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 121 28.What are the drawbacks of wind energy? a) Public resists for locating the wind forms in populated areas due to noise generated by machines and loss of aesthetic appearance. b) Wind forms located on the migratory routes of birds will cause hazards. 29.Write any four methods adopted for harnessing wind energy? a) Sky sail b) Ladder mill c) Kite ship (Large free flying sails). d) Sky wind power (Flying electric generator). e) Briza technologies (Hovering wind turbine). f) Sequoia automation (The kite wind generator). 30. What is a battery? How does it differ from a cell? A battery is an arrangement of several electrochemical cells, connected in series, that can be used as a source of direct electric current. Thus, A Cell: Contains only one anode and cathode. A Battery: Contains several anodes and cathodes. 31. What are the important requirements of a battery? A useful battery should fulfill the following requirements a) It should be light and compact for easy transport. b) It should have long life both when it is being used and when it is not used . c) The voltage of the battery should not vary appreciably during its use. 32. What are primary cells? Primary cells are cells in which the electrode and the electrode reactions cannot be reversed by passing an external electrical energy. The reactions occur only once and after use they become dead. Therefore, they are not chargeable. Example: Lechlanche’s cell. 33. What are secondary cells?Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 122 Secondary cells are cells in which the electrode reactions can be reversed by passing an external electrical energy. Therefore, they can be recharged by passing electric current and used again and again. These are also called Storage cells (or) Accumulators. 34. Write the overall equation for the reaction taking place in an alkaline battery? At anode: Zn (s) + 2OH(aq) -------> Zn (OH)2 + 2e-At Cathode: 2MnO2(s) + H2O +2e--------->Mn2O3 (s)+2OH(aq) Overall Cell Reaction Zn (s) + 2MnO2(s) + H2O --------> Zn (OH)2 (s) + Mn2O3 (s) 35.What are the advantages of alkaline battery over dry battery? (i) Zinc does not dissolve readily in basic medium. (ii) The life of alkaline battery is longer than the dry battery, because there is no corrosion on Zn. (iii) Alkaline battery maintains its voltage, as the current is drawn from it. 36.Write the cell representation of lead storage cell? The cell may be represented as: Pb /PbSO4 //H2SO4 (aq)/PbO2 /Pb 37. State the reaction when a lead storage battery is recharrged? The cell can be recharged by passing electric current in the opposite direction. The electrode reaction gets reversed. As a result, Pb is deposited on anode and PbO2 on the cathode. The density of H2SO4 also increases. The net reaction during charging is charging 2PbSO4 (s) +2H2O+ Energy Pb(s) + PbO2(s)+2H2SO4(eq) discharging 38.Write the charging and discharging reaction of lead accumulator?Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 123 charging 2PbSO4 (s) +2H2O+ Energy Pb(s) + PbO2(s)+2H2SO4(eq) discharging 39.What are the applications of lead acid storage cell? 1. Lead storage cell is used to supply current mainly in automobiles such as cars, buses, trucks, etc., 2. It is also used in gas engine ignition, telephone, exchanges, hospitals, power stations, etc., 40.Write the cell representation of NICAD battery? Cd │Cd(OH)2 ║ KOH(aq) │NiO(OH)│Ni 41.What are the advantages and disadvantages of NICAD battery? Advantage 1. It is smaller and lighter. 2. It has longer life than lead storage cell. 3. Like a dry cell, it can be packed in a sealed container. Disadvantage It is more explosive than lead storage battery. 42. How are the anodic and cathodic electro active materials made in Ni-Cd battery? (or) How is NICAD battery constructed? Nickel-cadmium cell consists of a cadmium anode and a metal grid containing a paste of NiO(OH) acting as a cathode. The electrolyte in this cell is KOH. 43.Which is the anode and cathode in a Nickel-cadmium battery? Anode : Anode in NICAD battery is cadmium. Cathode : Cathode is a metal grid containing a paste of NiO2. Electrolyte: KOH 44. Describe lithium battery? The lithium battery consists of a lithium anode and TiS2 cathode. A solid electrolyte, generally a polymer, is packed in between the electrodes. The electrolyte (polymer) permits the passage of ions but not that of electrons.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 124 45. List any two advantages of lithium batteries. (or) Lithium battery is the cell of future, why? (i) Its cell voltage is high, 3V. (ii) Since Li is a light-weight metal, only 7g (1 mole) material is required to produce 1 mole of electrons. (iii) Since Li has the most negative E0 value, it generates a higher voltage than the other types of cells. (iv) Since all the constituents of the battery are solids there is no risk of leakage from the battery. (v) This battery can be made in a variety of sizes and shapes. 46.What are the advantages of using lithium as anode in batteries? (i) Since Li has the most negative E0 value, it generates a higher voltage than the other types of cells. (ii) Since Li is a high–weight metal, onlyl7g (1 Mole) material is required to produce 1 mole of electrons. (iii) Its cell voltage is high, 3.0V BIG QUESTTIONS: 1. Write in brief about chain reaction and nuclear fission reactions?  Definition  Mechanism  Illustration  Characteristics 2. What are breeder reactors? Explain with an example?  Definition  Illustration  Significance 3. What are nuclear chain reactions? Expain how to improve the amount of nuclear energy with illustration?  Definition of nuclear chain reaction  Criteria of nuclear chain reaction i) Critical mass  Super critical mass  Sub-critical mass  Illustration  Definition of Nuclear energyEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 125 4. State the principle and application of solar batteries?  Definition of Solar cell batteries  Principle  Construction  Schematic representation  Working  Applications  Lighting purpose  Solar pumps run by solar battery  Advantages 5. Describe the construction and working of H2 –O2 fuel cell? (or) Give an account of H2 –O2 fuel cell?  Definition  Description  Working  At Cathode  At Anode  Cell reactions  Fuel battery  Advantages of Fuel Cells 6. Give an account of Light water nuclear reactor with a neat diagram? (or) Explain the power generation from light water nuclear reactor?  Definition  Components  Diagram  Working  Pollution  Problem on disposal of reactor waste 7. State any four characteristics of a nuclear fission reaction? 8. Describe the conversion of solar energy into electrical & Thermal energy?  Thermal conversion  Methods of thermal conversionEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 126 i) Solar heat collectors ii)Solar water collectors  Photoconversion  Methods of photoconversion 9. Describe using a block diagram the light water nuclear reactor for power generation? 10. Give an account of solar cells?  Definition  Priniciple  Construction  Working  Applications  Lighting purpose  Solar pumps run by solar battery  Advantages  Disadvantages  11. What are the components of a nuclear reactor? Write briefly about each component?  Definition & Example  Components of nuclear reactor  Fuel rods  Control rods  Moderators  Coolants  Pressure vessel  Protective shield  Turbine 12. Discuss the characteristics of the reaction when uranium undergoes nuclear fission?  Illustrate U235 fission chain reaction 13. Write a note on wind energy?Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 127  Definition  Methods of harnessing wind energy  Wind mills  Wind farms  Other methods  Advantages  Disadvantages 14. Write a note on Ni-Cd Battery?  Description  Representation  Working at cathode and anode  Overall reactions during use  Recharging the battery  Advantages  Disadvantages  Uses 15. Write a brief note on lead –acid storage cell?  Storage cell  Description  Representation  Working at cathode and anode  Overall reactions during use  Recharging the battery  Advantages  Disadvantages  Uses 16. Explain the construction and workings of lead acid battery (or) Lead acid accumulator ?  Construction  Overall cell representation  Working (Discharging)  At cathode and anode  Recharging the battery 17. Write notes on lithium battery?  Lithium battery  Uses  PurposeEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 128  Advantages  Lithium-TiS2 battery 18. What is reversible battery? Describe the construction and working of lead acid storage battery with reaction occuring during charging and discharging?  Definition and examples of reversible battery  Construction  Overall Cell representation  Working at cathode and anode  During charging and discharging 19. How is NICAD battery constructed. Explain with cell reaction? 20. Give an account of i) Lead-Acid and ii) Ni-Cd batteries  For both Lead-Acid and Ni-Cd  Working at cathode and anode  Overall cell reaction  Net reaction during charging  Advantages  Disadvantages  Uses 21. Describe the construction of nickel cadmium battery. Explain its working with the required cell reactions?  Construction  Overall cell representation  Working (Discharging)  At cathode and anode  Recharging the battery 22. Describe alkaline battery?  Description  Cell reactions At Cathode At anode  Overall cell reactions  AdvantagesEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 129 UNIT-V ENGINEERING MATERIALS Introduction: Engineering materials are those materials which are usually used in engineering applications in the regions field of science and technology. These materials in check abrasives, adhesives, lubricants, refractories, ceramics, glasses, metals, polymers, semiconductors and other multiphase systems. Engineering materials play important roles in mechanical and civil engineering fields, where very specific requirements are needed.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 130 Refractories Definition Refractories are the materials that can withstand high temperature without softening, melting or deformations in shape. Refractories are chemically inert and hard in nature. The major function of a refractory is to withstand high temperatures and to resist the abrasive and corrosive action of molten metals. Slugs and gases Characteristics of a Refractory  It should be infusible at high temperature.  It should be chemically inert towards corrosive gases, metals and slugs. Produced in the furnaces.  It should resist the abrasive action of their gases.  It should withstand the applied load of structure at operating temperatures.  It should have uniform expansion and contraction.  It should not get cracked at operating temperature.  It possesses low permeability.  It should have high refractoriness.  It should be able to withstand overlying load of structure, at operating temperature. Uses of Refractories 1. They are used in making cracibs for processing materials at high temperature. 2. They are mostly used for the construction of hining of fiarneces, kilns etc., 3. They are also used in the production manufacturing like cement, gases, ceramics, paper, metals.(both ferrous and non-ferrous) etc., Classification of Refractories Refractories are majorly classified into two ways on the basics of the chemical properties of their constifent substancesand their refractories. According to their chemical properties REFRACTORIESEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 131 Acidic Basic Nentral Refractories Refractories Refractories Ex: Silica Ex: Magnestie Ex:Graphite Alumina Dolomite Carborundum Acidic Refractories: They contain acidic materials like alumina (Al2O3) and silica (SiO2) and are not attacked by acidic materials. They are easily attacked by basic materials. Ex. : Alumina, Silica fire clay refractories. Basic Refractories They are basic materials like CaO, MgO etc., and not attacked by basic materials. They are easily attacked by acidic materials. Ex.: Magnésite, Dolomite, Carome Magnésite. Neutral Refractories: They are made from weakly acidic /basic materials like carbon, chromite Zirconia, etc., but remain naffected by acidic or basis materials. Ex: Graphite, Chromite, Zirconia, Carborundum refractories. According to their refractoriness: S.NO TYPE OF REFRACTORIES PCE VALUE REFRACTORINESS(0C) EXAMPLES 1 Low heat duty refractories 19-28 1520 – 1630 Silica bricks 2 Intermediate heat duty refractories 28-30 1630 – 1670 Fireclay bricks 3 High heat duty refractories 30-33 1670 – 1730 Chromite bricks 4 Super heat duty refractories >33 >1730 Magnesite bricks Based on the oxide content, they also classified as. 1) Single oxide refractories Ex.: Alumina Magnesia Zirconia 2) Mixed oxide refractories Ex.: Spinel, MulliteEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 132 3) Non-oxide refractories Ex.: borides, Carbides, Silicates Properties of Refractories Refractoriness It is the ability of the refractory materials to withstand the heat without softening or deformation under the working conditions. Usually refractories of materials are measured by measuring its softening or fusion temperature higher than the operating temperature of the industries. Ex.: Fire cky bricks (1600 – 1750’C) Bancite bricks ( 1730 – 1850’C) Chronite bricks (1950 – 2200’C) Zirconta bricks (2200 – 2700’C) The refractoriness of determined by means of the standard PCE (Pyrometric Cone Equivalent) Test. Pyrometric Cone Equivalent (PCE) Pyrometric Cone equivalent is the number, which represents the softening temperature of a refractory specimen of standard dimension (38mm height and 19mm triangular base) and composition. Ex: S.No. Refractory PCE. Number Softening temperature 1 Silica bricks 28.32 17100C 2 Alumina bricks 36.38 1800-18500C 3 Magnesite bricks 38 18500C Objectives of PCE Test: (i) To determine the softening temperature of a test specimen material (ii) To classify the fire clay refractories. (iii) To check and determine the purity of the refractories. (iv) To check the uniformity of the composition of the materials and its protnests.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 133 Measurement of PCE The Rafractoriness is commonly measured by compuring the softening temperatures of the test cones. Pyrometric cones are pyraming shaped standard refractory of definite prepositions (or) COMPOSITION AND dimensions and also having definite softening temperatures. A test cone is prepared from a refractory material, which the softening temperatire of a test cone is to be determined, as similar to pyrometric cones. The test cone is piaced on an electric furnare along pyrometric cones. The furnace is heated at a standard rate of 100C per miniute, during softening of pyrometric cones occur along with test cone. The temperature at which the apex of the cone touches the base is taken as it softening temperature. A good refractory should have high refractoriness. 1. Refractoriness Under Load (RUL) The temperature at which the refractory deforms by 10% is called refractoriness under load (RUL) A good refractory material must possess high mechanical strength to withstand compressive loads, tension and stress without deformation at high temperature. Generally softening temperature decreases with respect to increase of the load. The capacity of load bearing character can be measured by RUL Test. RUL Test:Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 134 It is conducted by applying a constant load of 1.75 kg. cm2 ON test material of size 5cm2 and height 75 cm and heating on a carbon resistance furnace at a standard rate of 100C per minute.  A good refractory should have high RUL value. Porosity A good refractory should have the low porosity. Porosity may be defined as the ratio ot its pore volume to the bulk volume. Porosity P = W -D X 100 W -A Where W -weight of sationated specimen D -weight of dry specimen in air A -weight of saturated specimen submerged in water Porosity is an important property of a refractory. It decreases the strength, resistance to abrasion, chemical stability and thermal condnecivity. Advantages of high porosity refractory (i) High porous refractory increases resistance to thermal spalling. (ii) High porous refractory material possess lower thermal conduetivity due to presence of more roids. Disadvantages of high porosity refractory (i) It reduces the strength of the material. (ii) It also reduces resistance to abrasion. (iii) It reduces the resistance to corrosion.  A good refractory should have low porosity. Thermal spalling Thermal spalling is the property of breaking, cracking, peeling off a refractory material under high temperatures. A good refractory must show a very good resistance to thermal spalling. Thermal spalling is mainly due to, i) Rapid change in temperature: This causes uneven expansion and contraction within the mass of the refractory which loads to the development of internal stress and strain that loads to spalling ii) Slag penetration into the refractory brick: This causes the variations in the coefficient of expansion and loads to spalling. A good refractory material should have low co-efficient of expansion.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 135 Spalling can be reduced by i) Using high porosity, low coefficient of expansion and high thermal conductivity refractory bricks. ii) Avoiding sudden temperature changes. iii) By modifying the furnace design so that stress is not setup, when the furnace is heated. iv) Preventing slag penetration. v) Overfiring the refractories at high temperatures for sufficienty long time, that making the material less susceptible to uneven expansion and contraction, when heated. Properties like Permeability, Bulk density, Thermal conductivity, Chemical inertness, Thermal expansion, Electrical conductivity, Texture, Resistance to abrasions and Heat capacity are other important factors of a refractory. Manufacture of Refractories: Manufacture of a refractory consists of the following steps: 1. Crushing: The raw materials in the form of big lumps are crushed to about 25mm size. 2. Grinding: The crushed materials are ground down into 200 mesh size by using crushers, pulverizers, hammer mills, ball mills, and screens. The ratio of coarse to fine particles should be even. 3. Screening: It involves the purification of the refractory raw materials. It is essential to remove the unwanted materials from the raw materials for producing better refractories. This is done by (a) setting (b) magnetic separation and (c) chemical methods. 4. Storage: After screening and mineral operating dressing, the pure materials are stored in storage bins with bucket elevators. 5. Mixing: It is done for the proper distribution of the plastic materials throughout the mass. This makes moulding easier. 6. Moulding:Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 136 Moulding can be done by hand or mechanically. Mechanical – moulding produces refractories having more density and strength than that produced by hand-moulding. De-moulding of the refractory material is essential for increasing the density and the strength of the refractory by mechanical moulding. 7. Drying: Slow drying is employed to remove the moisture from the Refractories which help to avoid voids and high shrinkage. So drying mobilizes the strength of the refractory and making it safe for subsequent handling. 8. Firing: The Refractories are fired in kiln at a temperature as high as or higher than their use temperature to stabilize and strengthen their structure. Depending upon the nature of the bricks the firing temperature will be different. Firing helps (a) to remove water of hydration (b) to impart high crushing strength (c) to facilitate development of stable mineral forms to the finished products. Manufacture of common Refractory: Alumina Bricks (or) Fire Clay Bricks: Alumina bricks contain 50% or more of Al2O3. They are generally manufactured by mixing calcined bauxite (Al2O3) with clay binder. Note: Calcination: Heating the ore in absence of air Manufacturing: 1. Grinding and Mixing The raw materials (calcined bauxite & SiO2) and calcined fire clay are ground to fine power and are mixed with required amount of water to convert it into pasty material. 2. Moulding: The pasty material is converted into bricks by the general moulding technique like machine pressing or slip casting. 3. Drying and firing: The bricks after moulding is dried slowly to remove the moisture and then fired in continuous kiln or tunnel kiln to about 1200 – 14000C for 6-8 days.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 137 Properties:  Alumina bricks are acidic refractories.  They posses very high coefficient of expansion.  They also posses high porosity, and high temperature load-bearing capacity.  They are inert to the action of gases like CO2, H2 and natural gas.  They are also very stable to both in oxidizing and reducing conditions.  They posses better resistance to thermal spalling. Uses:  Medium-duty bricks (containing 50 to 60% Al2O3), which is used in linings of cement rotary kilns, soaking pits, reheating furnaces and walls etc., which are subjected to high abrasion.  High-duty bricks (containing 75% Al2O3) which is used in hottest zones of cement rotary kilns, lower parts of soaking pits, brass melting reverberatories, aluminium melting furnaces, etc.,  Fire clay refractories are largely used in steel industries. MAGNESITE BRICKS Magnesite bricks contain mainly MgO. They are generally manufactured by mixing calcined Magnesite with caustic magnesia or iron oxide as binding materials. Manufacturing of Magnesite Bricks 1. Grinding and mixing: The raw materials (calcined Magnesite) and binding materials (caustic magnesia (or) iron oxide are ground to fine powder and mixed with water to a pasty material. 2. Moulding: Moulding is usually done by machine pressing to a required shape. 3. Drying and firing: Drying is carried out at ordinary temperature to remove the moisture. Firing is done in a kiln at 15000C For 8 hours and then cooled slowly. Properties:  Magnesite bricks are basic refractories.  Magnesite bricks can be used up to 20000C without load and up to 15000C under a load of 3.5kg/cm2.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 138  They have good resistance to basic slags, but combine with H2O and CO2.  They possess good strength, little shrinkage.  They have poor resistance to abrasions.  They are used in steel industry for the lining of basic converters and open-hearth furnaces.  They are also used in hot mixer linings, copper converters and reverberatory furnaces. ZIRCONIA BRICKS Manufacture: They are prepared by mixing zirconite mineral (ZrO2) with colloidal Zirconia or alumina as binder and finally heated to 17000C, small amount of MgO or CaO is added as stabilizer because mineral zirconite undergoes volume changes on heating and cooling. Properties:  Zirconia bricks are neutral refractories.  Though Zirconia bricks are neutral, they are affected by acidic stags.  They can be used up to 20000C and up to 15000C under a load of 3.5kg/cm2.  They are also quite resistant to thermal shocks.  Their thermal expansion is low. Uses: They are used only where very high temperature is maintained, e.g., high – frequency electric furnaces. ABRASIVE Abrasive are hard substances, used for polishing, shaping, grinding operations. They are characterized by high melting point, high hardness and chemically inert. Characters of abrasive:  Characteristics of an abrasive are as follows  They are very hard.  They are chemically inert.  They have high melting point.  They possess high refractoriness.  They should not be affected by the fractional heat.  They should be resistant to mechanical shock.  They should resist the abrading action.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 139 Mohs scale of hardness Hardness is the most important property of an abrasive. It is the ability or capacity of an abrasive to grind away another substance. Mohs mineralogist has suggested a scale for determining the hardness of abrasive substances known as Mohs scale or Vickers ScaleEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 140 . In this scale’ the hardness of common abrasives are given in the increasing order. According to this scale’ talcum power is having the hardness of one and it is the softest material and the diamond is having the hardness of 10 and it is considered as the hardest material. The hardness of any material on Mohs scale therefore falls between 1 and 10. Name of the abrasives Chemical formula Mohs number Talc 3Mgo.4Sio2.H2O 1 Gypsum CASO4.2H2O 2 Calcite Caco3 3 Fluorine CaF2 4 Apatite CaF2.3Ca3(PO4)2 5 Feldspar K2O.Al2O3.6H2O 6 Quartz SiO2 7 Topaz AlF3.Sio2 8 Corundum Al2O3 9Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 141 diamond C 10 Abrasives having their hardness 1 to 4 in Mohs scale are called soft abrasives. E.g., talc, gypsum, calcite, etc. Properties of abrasives: Hardness It is the ability of an abrasive to grind or scratch away other materials. The harder the abrasive quicker will be its abrading action. Hardness of the abrasive is measured on Mohs scale or Vickers scale. Measurement of hardness using moh’s scale: Moh’s scale is a scale in which common abrasives (natural or artificial) are arranged in the order of increasing hardness. Talc, quartz, diamond have got 1,7,10 in moh’s scale abrasive having their hardness 1-4 in Mohs scale are known as soft abrasives. Toughness: Abrasives are generally hard and brittle, which is otherwise known as toughness. Abrasive power: It is the strength of an abrasive to grind away another material. It depends on hardness, toughness and refractoriness. Classification of abrasives: Natural abrasives Non-siliceous abrasives: Diamond: It is a pure crystalline carbon. It is the hardest known substance. It is chemically inert and not affected by acids or alkalis. The off-color diamond is called borts and black color diamond is called carbonado. Uses: It is used in drill points, cutting rocks, stones and grinding wheels. Corundum: It is a pure crystalline alumina (AL2O3). Its hardness on moh’s scale is 9. Uses: It is used for grinding glasses, gems, lenses, metals, etc. Emery:It is a fine – grained, opaque, black colored mineral. It consist of I. 55-75% crystalline alumina II. 20-40% magnesite III. 12% other minerals Uses: It is used in the tip of cutting and drilling tools, and also it is used in making abrasive paper and cloth. Siliceous abrasives:Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 142 Quartz:It is pure crystalline silica (SIO2) .its hardness is 7 on Mohs scale. Uses: It is used for grinding pigment in the paint industry and also it is used as granules in grinding machines. Garnet:It is a mixture of trisilicates of alumina, magnesia and ferrous oxide. Its hardness ranges from 6-7.5 on Mohs scale. Uses: It is used in making abrasive paper and abrasive paper and abrasive cloth, and also it is used in glass grinding and polishing and polishing metals. Synthetic abrasives Silicon carbide or carborundum (Sic) Manufacture: Silicon carbide is manufactured by heating sand (60%) and coke (40%) with some saw-dust and a little salt in an electric furnace to about 1500°C.saw-dust evolves gases during burning, which on circulation increases the porosity of the charge. Salt reacts with iron and other similar impurities present in the raw materials, forming volatile chlorides. This also increases the porosity of the final products. SiO2+ 3C→SiC + 2CO at (1500°c) The silicon carbide, removed from the furnace is then mixed with bonding agent (like clay silicon nitride) and then shaped, dried and fired. Properties:  Silicon carbide possesses a thermal conductivity, low expansion and high resistance to abrasion and spalling.  They are mechanically strong and withstand loads in furnace up to 1650°C.  Heat conductivity of SiC is intermediate between metals and ceramic materials. Uses:  Silicon carbides are used as heating elements in furnaces in the forms of rod and bars.  They are also used for partition walls of chamber kilns, coke ovens, muffle furnace, and floors of heat-treatment furnaces.  Sic bonded with tar are excelled for making high conductivity crucibles. BORON CARBIDE (B₂C) or NORBIDE:Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 143 Manufacture: It is prepared by heating a mixture of boron oxide (B₂O₃) and coke (carbon) in an electric furnace to about 2700°C. 2B₂O₃+7C→ B₄C + 6CO ↑ (at 2700°C) Properties:  Its hardness is 9 on Mohs scale.  It is light weight and black colored compound.  It is highly resistant to chemical attack and erosion.  It resists oxidation much better than diamond. Uses:  It is used as hard material for making grinding dies, and for cutting and sharpening hard high-speed tools.  It is used to prepare scratch and wear resistant coatings.  It is used in the nozzles for sand blasting ALUNDUM (Al2O3) Manufacture: It is prepared by heating a mixture of calcined bauxite, coke and iron in an electric furnace to about 4000°C.it is an artificial corundum. It is not as hard as carborundum but is less brittle and tougher. 4AR + 3O₂ → 2 AL₂O₃ Properties: i. It is not as hard as carborandum but it has brittle and tougher ii. It is stable at high temperature iii. It is very hard iv. It is resistant to hydration and to attack by acid Uses:  It is used in grinding of hard steels and other materials of high tensile strength.  It is also used in the manufacture of abrasive wheelsEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 144 APPLICATIONS OF ABRASIVES Abrasives are used in three forms. Example: quartz and garnet As abrasive paper or cloth Manufacture of abrasive paper and cloth: The roll of paper or cloth is made to pass through a series of rollers, and a thin coating glue is applied on its upper side. It is then passed under a hopper from which the gravel of abrasive is allowed to fall and spread evenly on the glued paper or cloth. Then it is dried in warm drying room. Finally it is allowed to age for few days, so that the glue sets firmly. Uses: It is used to prepare smooth wood, metal and plastic surfaces. Example: alumina and silicon carbide. 3. as grinding wheels Manufacture of grinding wheels: Grinding wheel is manufactured by mixing abrasive grains with binder. The mixture is molded into desired shape and heated and cured. Uses: It is used for the removal of scales from iron surfaces, cutting tool sharpening LUBRICANTS Lubricant: Lubricant is a substance used in between two moving surfaces to reduce the friction. Lubrication: Lubrication is a process of reducing the friction and wear between the two moving surfaces. Functions of lubricant 1. They reduce friction, wear and tear between the moving surfaces. 2. They are acting as an anti corrosion agent. 3. They reduce energy wastage and are cost effective. 4. They reduce the expansion of metal parts by local frictional heat. 5. They prevent the entry of dirt, dust and moisture between the moving parts. 6. In certain engines like internal combustion (IC) engines, the lubricant act as a fuel gasket and in aircraft .lubricant is used as a hydraulic fluid to change the pitch of the propellant. Important requirements of a good lubricant:  A good lubricant should not undergo any decomposition, oxidation, reduction at high temperature.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 145  A good lubricant should have higher flash and fire points than the operating temperature and low ash content.  A good lubricant should have higher flash and low ash content.  A good lubricant should have high oiliness, viscosity index aniline point.  A good lubricant should not corrode the machine parts.  It should not be harmful to the operator.  It should be cheap and easily available.  It should be chemically and thermally resistant. Classification of lubricants: Lubricants can be classified on the basis of their physical state and consistency. i. Solid lubricants: Ex: graphite, molybdenum, disulphide, etc ii. Semi solid lubricants: Ex: greases, Vaseline, etc iii. Liquid lubricants ( or) lube oil (or)lubricating oil Ex: a) vegetable oils: olive oil, palm oil, castor oil, etc. b) Animal oils: whale oil, shank oil, tallows oil, etc. c) Mineral oils or petroleum oils or blended oils: petroleum fractions and petroleum oils containing vegetable oil. d)synthetic oils: silicones, poly glycol, ethers, etc. e) Blended oils (or) compounded oils: mineral oils with various additives. iv. Emulsions a) Oil in water type: Ex cutting emulsions. b) Water in oil type: Ex cooling liquids. V. Gasses: Used in fans, compressors, etc Ex: air, H2 Features of lubricants:  Liquid lubricants or lubricating oils or lube oils Animal and vegetable oils These are glycerids of higher fatty acids and have very good oiliness. These oils cannot be used effectively due to the following reasons. They undergo oxidation at higher temperature and forms gummy and acidic products. They get easily hydrolysed under moist condition. So they are used as “blending agents” with other lubricating oils.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 146 Mineral oils and petroleum oils They are obtained by fractional distillation of crude petroleum oils, having carbon chain length varies from c₁₂ to c₅₀. It possess poor oiliness, which can be improved by mixing with animals or vegetable oils. These oils are cheap and quiet stable under normal conditions. Usually the minerals oils are contaminated with lot of impurities such as wax, asphalt, oxidisable impurities etc. these impurities are generally removed by following methods. A. Removal of waxes The wax can be removed by dewaxing process. In this process the petroleum oil is mixed with a suitable solvents such as propane, trichloroethylene etc and then cooled. The wax crystallises out and is removed by filtration. B. Removal of asphalt Asphaltic and naphthenic material can be removed by acid refining process, in which the dewaxed oil is treated with con.H₂SO₄ and then agitated. Some of the unwanted impurities get dissolved in acid, while others converted in to sludges. The sludge is removed by filtration. The filtrate is neutralizing with calculated quantity of NaOH to neutralize the acid. C. Removal of sulphur Sulphur can be removed from the oil by desulphurization process, in which the oil is treated with hydrogen in the presence of nicle as a catalyst. During this process, the unsaturated compounds are converted to the saturated compounds. D. Removal of colored substances These substance and micro crystalline waxes can be removed by filtration through fuller’s earth. Blended oils By the addition of suitable additives like castor oil, coconut oil, oleic acid, palmitic acid, phenols, polyester, n-hexanol etc. the various properties of the lubricating oils cans be improved. Such lubricating oils having improved properties are called ‘Blended oils’ (or) ‘compounded oils’. Some of the important additives and their functions S.No Name of the additive Examples functions 1. antioxidants Aromatic amino compounds. Phenolic compounds To avoid oxidation of the oil and prevent the formation of gum likeEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 147 substance 2. Corrosion inhibitors Organic pb and sb compounds They are adsorbed on metal surface,thereby protecting the surface from attack of moisture. 3. Natiwear agentsor extreme pressure additives Organic compounds having S,P,Cl etc They react with metal surface forming surface film of lower shear strength and high melting point. 4. Detergents or deposit inhibitors Salt of phenols or salt of carboxylic acid,sulphonates They prevent foreghn particles and carbon deposits in engines which block the passage of oil. 5. Pour-point depressants Phenols ,poly alkyl benzene ,chlorinated wax with naphthalene They prevent separation of wax from the lubricating oil 6. Viscosity index improvers n-hexanol,poly iso buttylene ,poly alkyl benzene,poly metha acrylates They prevent the oil from thinning at higher temperatures and thickening at lower temperatures 7. Foam inhibitors (or) antifoaming Methyl silicone polymers Reduces foaming 8. Oiliness carriers Fatty acids such as stearic acid ,palmitic acid ,oleic acid They increase the oiliness or adhering property of the lubricants. 9. thickeners Polyesters, polystyrene They increase the viscocity of the lubricants c) Silicone oils (Or) liquid silicones (or) silicone fluids Silicone oils are relatively low molecular weight silicones or silicon polymers.Dimethyl silicones or methyl and phenyl silicones are commonly available silicones are commonly available silicone oils. Hydrolysis of chlorotrimethyl silane with water yields monohydroxy compounds, which spontaneously condenses to form hexamethyl disiloxanes 2(CH₃)₃SiCl+2HEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 148 Hydrolysis of dimethyl dichlorosilane give a linear polymer, whereas, hydrolysis of trichloromethsilane gives a network polymer. Properties: 1. They are odourless , tasteless ,inert and possess constant physical properties over a wide range of temperature (-70°C to 200°C). 2. The viscosities of silicone oils ranges from 5 to 106 m pas. 3. They exhibit pour points between -60°c to 35°c, its viscosity is weakly depends on temperature. 4. In comparion with hydrocarbons oils, they are more stable to high temperatures, stress and oxidative degradation. 5. Silicone oils containing phenyl groups exhibit the highest thermal stability , these can be used for months at 250°C in iar but up to 3oo°C in closed systems. USES: 1. Silicone oil is used a very good lubricant without softening. 2. Silicone oil is used as polish additives in polishes for cars,furnitures and cosmetics, because of its water repelling property. 3. They are used flow and gloss improvers in paint industry. 4. They can be used as water repellant finishes for large number of natural and synthetic textiles. 5. Silicone oil is used as a release agent in moulds , in the manufacture of rubber tyres ,plastics and also in the casting of metals. (e) Synthetic lubricants Synthetic lubricants can meet any requirements, under drastic and severe conditions .in air craft engines, same synthetic lubricant (eg.organic amines, imines or amides) can be used in the temperature range of -50°C and 250°C.these lubricants should have low freezing point, high viscosity index and they should be non inflammable. Such lubricants can be synthesized and successfully utilized in severe operating conditions are called synthetic lubricants. Eg. Silicones, polyglycol, ethers, organic amines. Gas Lubricants In gas lubrication there is negligible wear of machinery lower chance to radiation damage, no risk of contamination and long life. In the case of gases, viscosity is low and is independent of temperature and pressure. But gases have no boundary lubricating properties. Moreover there is a chance for some wear during the starting and stopping of the machinery. Usesi. Gas lubricants are used in precision spindles and gyroscopes. ii. They are also used in compressors, fans, etc.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 149 Lubricating Emulsions Lubricating Emulsions are of two types (a) Oil in-water emulsions, (b) Water in-oil emulsions (a) Oil in-water emulsions: They are obtained by adding less quantity of an oil containing water soluble emulsifying agent (3-20%) to a suitable quantity of water. Usual emulsifying agents are sodium soaps and salts of sulfonic acids. These emulsions are used in internal combustion engines, and marine diesel engines. In addition to the lubrication and cooling, they protect the machine parts from rust. e.g., cutting emulsions. (b) Water in oil emulsions: They are prepared by mixing water containing 1 to 10% water soluble emulsifier with oil. Alkaline earth soaps are used as an emulsifiers. These lubricants are usually used in compressors and pneumatic tools. e.g., cooling liquid. Properties of Lubricants Properties of Lubricants are viscosity, viscosity-index, flash and fire points, cloud and pourpoints, oiliness, emulsification, volatility, carbon residue, corrosion stability, decomposition stability, aniline point, precipitation number, sp. gravity, ash content, neutralization number, saponification number and mechanical stability. Among the above properties, viscosity and viscosity index, flash and fire points-, cloud and pour points and oilness will be discussed below. 1. Viscosity Viscosity is the property of a liquid or fluid by virtue of which it offers resistance to its own flow. It is the most important property since it determines the operating characteristics of the lubricant. If the viscosity of the oil is low, the oil film can riot be maintained between two moving surfaces. This results in excessive wear. If the viscosity is high, excessive friction will result. So a good lubricant should have moderate viscosity. The viscosity of a lubricant can be measured experimentally by Red wood or Say bolt or Engler or U-tube viscometers depending upon the nature of the lubricants. Viscosity-Index and the Effect of Temperature on Viscosity A lubricating oil becomes thinner when the operating temperature increases. It is due to the decrease in viscosity with increase in temperature. For a good lubricant, its viscosity should not change with change in temperature, so that it can be used continuously, under varying conditions of temperature. The rate of change of viscosity with temperature is expressed by a scale is known as viscosity-index (VI). It is defined as the average decrease in viscosity per degree rise of temperature between 100°F and 210°F. It is a graphical representation. If the viscosity of an oil falls rapidly as the temperature is raised, it has a low viscosityinddexEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 150 Example: Gulf coast oil (naphthenic hydrocarbons) and its viscosity-index is arbitrarily fixed as zero. If viscosity of an oil is affected slightly with Increase of temperature, it has high viscosity index. Example: Pennsylvanian oil (paraffinic hydrocarbons) and its viscosityindex value is arbitrarily fixed as 100. Determination of Viscosity -Index (V.I) The viscosity-index of the test oil is calculated by comparing the viscosity of the test oil at 100° F (38°C) with the viscosity of the zero viscosity-index Gulf coast oil and hundred viscosity index pennsylvanian oil both having the same viscosity as the test oil at 210° F (99°C) . There are three different steps in this measurement. Step 1 : Find out the viscosity of the test oil at 100° F and 210° F. Let 'V' be the viscosity at 100° F and 'V' be the viscosity at 210° F. If the difference between these two values is low, the oil is good and high if the oil is poor. Step 2 : Select a high-viscosity standard oil (i.e., pennsylvanian oil of V.I = 100) having same viscosity at 2100 F as the test oil, its corresponding viscosity at 100° F is found out. Let it be 'H'. Step 3 : Then select a low-viscosity standard oil (i.e. Gulf coast oil of V.I.=0) having the same viscosity at 210° F as the test oil, its viscosity at 100° F is found out Let it be 'L', then Viscosity Index (V.I.) = L U L H  x 100 Where U = Viscosity of the test oil at 100° F L = Viscosity of the low-viscosity standard oil at 100°F having the same viscosity at 210°F as the test oil. H = Viscosity of the high-viscosity standard oil at 100°F having the same viscosity at 210° F as the test oil. Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 151 Fig. Viscosity -temperature curves for the standard oils (L & H) and the oil under test (U) 3. Flash and Fire points Flash point : It is the lowest temperature at which the oil lubricant gives off enough vapours that ignite for a moment, when a tiny flame is brought near to it. Fire point: It is the lowest temperature at which the vapours of the oil burn continuously for at least five seconds, when a tiny flame is brought near to it. Normally, fire points are 5 to 40° higher than flash points. A good lubricant must have high flash and fire points. Significance Flash points and fire points are important when oils are exposed to high temperature service. A knowledge of flash and fire points is useful in providing safe-guards against fire hazards during use and transport. Flash point is an indication of the oil to volatilise and the level of storage of the lubricant. Paraffinic lubricants have higher flash points than that of the naphthenic lubricants. So the type of petroleum oils can be identified by the flash point determination. Determination The flash and fire points are usually determined by using Pensky-Marten's apparatus. The test oil is taken in the oil cup and heated by using water bath at the rate of raising the oil temperature 5°C per minute. The oil is stirred at the rate of 1 to 2 revolutions per second. The test flame is introduced for a moment at every 10 rise of temperature. The temperature at which a distinct flash appears inside the cup is noted as the flash point. The heating is continued and the temperature is again noted at which the oil ignites and continues to bum at least for 5 seconds. This temperature is taken as the fire point of the oil.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 152 Pensky-Marten’s Apparatus 4. Cloud and Pour Points Cloud point: The temperature at which an oil becomes cloudy or hazy in appearance when it is cooled slowly is called the cloud point. On cooling the oil, impurities like wax. Asphalt, etc., present in the oil crystallise out, and causing the oil, turbid. Significance: Knowledge of cloud point is useful in predicting the lowest temperature upto which the machine can be operated without any risk of jamming. Pour point: It is the temperature at which the oil ceases to flow or pour when it is cooled slowly below the cloud point. Below the cloud point, the oil itself crystallize out and minute crystals of wax become interlocked and therefore the flow is arrested. Significance: A knowledge of pour point helps to fix the 100vest temperature up to which the flow of lubricant is reliable. The cloud and pour points should be low for a good lubricant. They indicate the suitability of lubricants in cold conditions. The cloud and pour points can be lowered.  by lowering the viscosity of the oil  by dewaxing  by adding pour point depressant like poly alkyl benzene Determination Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 153 The cloud and pour points can be determined by using an apparatus called pour-point apparatus. It consists of a flat bottomed tube enclosed in an air jacket (Fig. 5.8). The jacket is surrounded by freezing mixture taken in a jar. The tube is half filled with oil. Every degree fall of temperature of the oil is noted by taking the tube outside the air jacket for a moment means of a thermometer introduced in the oil. The temperature at which cloudiness is noticed is taken as the cloud-point. Cloud and Pour-Point Apparatus The cooling is continued and the tube is taken outside after every 3°C fall of temperature and tilted to observe the flow or pour of the oil. The temperature at which the oil does not flow in the tube even when kept horizontal for 5 seconds is noted as the pour-point. 5. Oiliness: Oiliness is an important property of a lubricant and~ it is a measure of its capacity to stick on to the metallic surfaces under the conditions of heavy pressure or load. When a machine is subjected to high pressure operation, a poor oiliness lubricant will be squeezed out of the lubricated machine parts and a good oiliness lubricant will stay in between the lubricated surfaces. Vegetable oils have good oiliness but mineral oils have poor oiliness. By adding higher fatty acids like stearic acid, oleic acid or by adding vegetable oils, the poor oiliness of a lubricant can be improved. A good lubricant must have good oiliness. Mechanism of Lubrication or Types of Lubrication Lubrication takes place mainly by three types of mechanisms. (i) Fluid-film or Thick-film or Hydrodynamic Lubrication Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 154 In this mechanism, a thick film of fluid separates the moving surfaces each other. This leads to avoid the surface-to-surface contact and the welding of junctions (Fig. 5.9). So this reduces the wear and only the resisting factor to the movement of sliding/moving part is due to the internal resistance between the particles of the lubricant. So the lubricant should have the minimum viscosity and it should remain in place and separate the surfaces. In this condition friction is a function viscosity, thickness of the lubricant, relative velocity, and area of the moving /sliding surfaces. Hydrocarbon oils are the suitable lubricants for fluid-films lubrication. Watches, clocks, guns, sewing machines, scientific instruments, etc are provided with this type of lubrication. Fluid Film Lubrication (ii) Boundary Lubrication or Thin film lubrication In certain conditions when (i) the load is very high (ii) the viscosity of the oil is too low (ii) the shaft starts moving from rest (iv) the speed is very low, the clearance space between the moving/sliding surfaces is lubricated with an oil lubricant. A thin layer of the lubricant is absorbed by physical or chemical or both forces on both the metallic surfaces. These prevent the direct metalmeeta contact. The layers of the adsorbed lubricant carry the load. Coefficient of friction in this case is more than that in the thick film lubrication. Vegetable and animal oils (i.e., glycerides of higher fatty acids) and their soaps can be used as an effective lubricant in this case. Open gears, chains, cast iron bearing, internal combustion engines, etc. are provided with boundary lubrication. Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 155 Boundary Lubrication (iii) Extreme -Pressure Lubrication Extreme-pressure conditions in the moving metallic parts create high local temperature. This will cause the decomposition and evaporation of oil lubricant. In this situation special additives are added to mineral oils, and they are called “extreme-pressure additives”. These additives help to form more durable films on metal surfaces, which can withstand very high loads and temperatures. These additives are organic compounds such as chlorinated esters, su1phuried oils, tricrysyl phosphates having active radicals, which form high melting compounds on the metallic surfaces. Boilers, compressors, lathes, grinding machines, railway track-joints, etc. are provided with this type of lubrication. NANO MATERIALS Nano science is the revolutionary science and art of matter at the atomic, molecular or macro molecular scale that has cut across disciplines, such as chemistry, physics, biology and engineering. Nano technology is the design, characterisation, production and application of structures, devices and systems by controlling shape and size at the nanometer scale. A nanometer is one thousand millionth of a meter. For comparison, a single human hair is about 80,000 nm wide a red blood cell is approximately 7,000 mm wide. Nano materials are materials with very small dimensions consisting of atomic or molecular aggregates commonly called as nano particles possessing sizes of the order of 1 to 100 mm. CARBON NANOTUBES (CNTs) In 1991, Sumio Iijima discovered carbon nanotubes (CNTs). A carbon nanotube is a cylindrical rolled up sheet of grapfzene, which is a single layer of graphite atoms arranged in a hexagonal pattern. The chemical bonding of nanotubes is compressed entirely of sp2 bonds. This bonding structure, which is stronger than the sp3 bonds found in diamond, provides the molecules with their unique strength. Their hexagonal structure gives them great tensile strength and elastic properties. They also transfer heat very efficiently. CNT is 100 times stronger than steel but 6 times Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 156 lighter weight. There are three distinct ways in which a graph sheet can be rolled into a tube. They are: Types of Nanotubes Two different types of nanotubes are (i) Single-walled carbon nanotubes (SWCNT) It is a single cylinder with diameter 1-2 nm and a length of 100 m, making it effectively a one dimensional structure called a nanowise. Single-walled carbon nanotubes (i) Armchair Nanotubes Here a carbon-carbon covalent bond is parallel to the axis of the nanotube. Armchair Nanotubes (ii) Zig-zag nanotubes In this carbon-carbon covalent bonds down the centre. Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 157 Zig-Zag nanotubes (iii) Chiral Nanotubes It exhibit a twist or spiral around the nanotube. This orientation helps to determine the electrical properties of the nanotube. (iv) Multi-Walled Carbon Nanotubes (MWCNT) It consists of multiple concentric nanotube cylinders. Production of Carbon Nanotubes There are three methods to produce CNT in bulk quantities and at a lower cost. (a) Carbon arc method (b) Chemical vapour deposition method (c) Laser evaporation method (d) Pyrolysis of hydrocarbon (a) Carbon arc method It involves passing a current of about 50 amps between two graphite electrodes in an atmosphere of helium. This causes the graphite to vapourise, some of it condensing on the walls of the reaction vessel and some of it on the cathode. It is the deposit on the cathode, which contains the carbon nanotubes. Singled walled nanotubes are produced when cobalt, nickel or iron is incorporated as a catalyst in the central region of the anode. If no catalysts are used, multiwalled nanotubes are formed. (b) Chemical Vapour Deposition Method Carbon nanotubes can also be made by passing a carbon-containing gas, such as a hydrocarbon, lover a catalyst. The catalyst consists of nano-sized particles of metal, usually iron, cobalt or nickel. These particles catalyses the breakdown of the gaseous molecules into carbon, and a tube then begins to grow with a metal particle at the tip. The perfection of carbon nanotubes produced in this way has generally been poorer than those made by arc evaporation. (c) Laser evaporation method This is an important method for making carbon nanotubes. Nanotubes of 10 to 20 nm in diameter and 100 m long can be made by this method. A quartz tube filled with argon gas and a graphite target are heated at high temperature. The graphite target contains catalysts like cobalt or nickel in small amounts. An intense pulsed laserEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 158 beam is incident on the target, evaporating carbon from the graphite. The argon gas then drives the carbon atoms from the high temperature zone to the water cooled copper collector present somewhat outside the furnace. On which they condense into nanotubes. (d) Pyrolysis of hydrocarbon They can be synthesized by the pyrolysis of hydrocarbons like acetylene at about 700°C in the presence of Fesilica or Fegraphite catalyst under inert conditions. Applications of carbon nanotubes 1. Storage Devices In batteries, some charge carriers can be stored in nanotubes (i) Fuel Cells : Hydrogen can be stored in CNTs which can be used in the development of fuel cells. Carbon nanotubes are able to store hydrogen and could provide the safe, efficient, and costeffeectiv means to achieve this goal. Hydrogen atoms bond to the carbon atoms of the nanotube, and can be later released with slight changes in temperature and pressure. (ii) Lithium/Nickel Battery: Lithium atoms are very good charge carriers and can be store inside the carbon nanotubes. Normally one Li atom can be stored within six carbon atoms. 2. Protective Shields CNTs are poor transmitter of electromagnetic radiation and hence can be used as light weight shielding materials for protecting electronic equipment against electromagnetic radiations. 3. Sensors of gases (Chemical sensors) Cases like N02 an NH3 can be easily sensed /detected when they flow over CNTs. The electrical conductivity of CNTs increases when the gases are passed through them. When the gas molecule bind on to the CNTs, the concentration of holes in CNTs increase as the charge is transferred from CNTs to NO2 Semiconducting carbon nanotubes display a large change in conductance (i.e, ability to tear charge) in the presence of these gases (i.e. N02 and NH3). Researchers have detected minute amounts of sarin gas in under 4 seconds using a prototype nanotube gas sensor (previous sensors took over a minute to detect the same amount). In the future, nanotube sensors could be use for security and environmental applications. 4. Drug delivery vessels (Drug delivery with Buckyballs) Drug molecules can be attached to fullerene. The medicine loaded fullerene can then be attached to an antibody. Antibodies are V-shaped proteins that can recognize and attach to things in the body called antigens. Viruses, bacteria and diseases in the body each have unique antigens. The antibody finds the disease in the body then the attached fullerene delivers the appropriate medicine. Just like with magnetic nanoparticles, medicine can be sent only to place where it is needed, leaving healthy cells alone.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 159 5. Atomic Force Microscopy (AFM) Probe Tips CNTs attached to the tips of scanning probe microscope have been used to image biological and industrial specimens'. Single-walled carbon nanotubes have been attached to the tip of an AFM probe to make the tip “sharper”. This allows much higher resolution imaging of the surface under investigation; a single atom has been imaged on a surface using nanotube-enhanced AFM probes. Also, the flexibility of the nanotube prevents damage to the surface and the probe tip if the probe tip happens to "crash" into the surface. 6. Flat Panel Display Screens When a nanotube is put into an electric field, it will emit electrons from the en of the nanotube like a small canon. If those electrons are allowed to bombard a phospar screen then an image can be created. 7. Nano Composite Materials Nylon can be mixed with carbons fibers (100-200 nm diameter threads made in a similar manner to nanotubes), creating a nano composite material that could be injected into the smallest gear mold. The carbon fibers have excellent thermal conductivity properties that cause the nanocomposite material to cool more slowly and evenly allowing for better molding characteristics of the nanocomposite. Composites of aluminium of powder mixed with 5% CNTs possess a greater tensile strength compared to pure aluminium sheets. 8. Actuarors /Artificial muscle An actuator is a device that can induce motion. In the case of a carbon nanotube actuator, electrical energy is converted to mechanical energy, causing the nanotubes to move. Two small pieces of "buckypaper", paper made from carbon nanotubes, are put on either side of a piece of double -sided tape and attached to either positive or a negative electrode. When current is applied and electrons are pumped into "One piece of buckypaper and the nanotubes on that side expand causing the tape to curl in one direction. This has been called an artificial muscle, and it can produce 50 to 100 times the force of a human muscle the same size. Applications include robotics, prosthetics. 9. Nanoscale Electronics The mechanical and electrical properties of carbon nanotubes can be used to produce molecular electronic devices. Semi conducting nanotubes could be used as compact, more efficientEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 160 alternatives to conventional transistors. The integrated memory circuits made of nanotube composites with conducting polymer are found to be effective devices. 10. Quantum wires Quantum wires are made of carbon nanotubes have high electrical conductivity. 11. Catalysts They can be used as good catalysts in some chemical reactions. (i) Reduction of NiO : Nickel oxide (NiO) can be readily reduced to Ni metal. NiO CNT  Ni (ii) Reduction of AICI3 AICl3 can be reduced to its base metal. AlCl3 CNT  Al CNT in Fuel Cell Carbon nanotube have applications in battery technology lithium, which is a charge carrier in some batteries, can be stored inside nanotubes. It is estimated that one atom can be stored for every six carbons of the tube. Storing hydrogen in nanotubes is another possible application, one that is related to the development of fuel cells as sources of electrical energy for future automobiles. Principle A fuel cell consists of two electrodes separated by a special electrolyte that allows hydrogen ions, but not electrons, to pass through it. Hydrogen is sent to the anode, where it is ionized. The freed electrons travel through an external circuit wire to the cathode. The hydrogen ions diffuse through the electrolyte to the cathode, where electron, hydrogen and oxygen combine to form water. The system needs a source of hydrogen. One possibility is to store the hydrogen inside carbon nanotubes. It is estimated that to be useful in this application the tubes need to hold 65% hydrogen by weight. At present only about 47% hydrogen by weight has been successfully put inside the tubes. Working of fuel cell with CNT An elegant method to put hydrogen into carbon nanotubes employs the electrochemical cell.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 161 Carbon Nanotubes in Fuel cell Single walled nanotubes in the form of paper are the negative electrode in a KOH electrolyte solution. A counter electrode consists of Ni(OH)2. The water of the electrolyte is decomposed into positive hydrogen ions (H+) that are attracted to the negative single walled nanotube electrode. The presence of hydrogen bonded to the tubes is indicated by a decrease in the intensity of a Raman active vibration. CATALYSIS Chemical catalysis benefits especially from nanotubes due to the extremely large surface to volume ratio. Example (a) Nested nanotubes with ruthenium metal bonded to the outside have been demonstrated to have a strong catalytic effect in the hydrogenation reaction of cinnamaldehyde. C6H5Cll= CHCHO in the liquid phase compared with the effect when the same metal ruthenium is attached to other carbon substrates. (b) Chemical reactions have also been carried out inside nanotubes. Nickel oxide (NiO) is reduced to base metal Ni and Aluminium chloride (AICI3) is reduced to base metal Ai. A steam of hydrogen gas at 475°C partially reduces MoO3 to, MoO2, with the accompanying formation of steam H20, inside the multi walled nanotubes. Cadmium Sulphide (CdS) crystals have been formed inside nanotubcs by reacting Cadmium Oxide (CdO) crystals with H2S gas at 400°C. PART-A 1. Define refractories. How can they be classified? 2. Give any four characteristics of refractories. 3. What is refractoriness? How is it measured? 4. What is Segar cone test (or) PCE test? 5. What is RUL test? Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 162 6. Name the stages in manufacture of refractory? 7. What is porosity of a refractory? How can it be modified? 8. What is thermal spalling? How will you control it? 9. What are the two types of dimension change? 10. Name two refractories which should not be kept in direct contact with fireclay refractory. Why? 11. What are abrasives? 12. What is abrasive powder? 13. What is moh’s scale? 14. How is carborundum prepared? 15. What is norbide? How can it be prepared? 16. Give the applications of garnet and emery. 17. What are the applications of abrasive? 18. How can we classify the abrasives? Give eg for each type. 19. Define lubricant. Classify them. 20. What is flash and fire point. 21. Define viscosity index. 22. Define cloud and pour point. 23. What are pour point depressants? Give eg. 24. What are greases? How can they be classified? 25. What are carbon nanotubes? What are the types? 26. What are nano materials? 27. What is nano chemistry? 28. Write down the synthetic methods to prepare carbon nanotubes. 29. Write any four applications of carbon nano tube. 30. Mention the various forms of SWNT. PART-B 1. Classify the refractories. Explain one example for each type. 2. What are the properties of refractory? Explain any three of them. 3. Write notes on alumina, Zirconia and Magnesite bricks. 4. Write a note on synthetic abrasives. 5. What is your understanding about natural abrasives? 6. How will you explain the mechanism behind the lubrication? 7. Explain any four properties of lubricants? 8. How can you classify lubricants? Explain. 9. Write notes on solid lubricants. 10. Bring out the important applications of CNT. 11. Write a note on structure and synthesis of CNT. PART-B BIG QUESTIONS 1. Explain the characteristics or requirements of a good refractory.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 163  Infusible  Inert  Resistance  Withstand power 2. Explain the classification of refractories.  Based on their chemical properties  Based on their refractoriness 3. What is meant by refractoriness? Explain how is it measured?  Definition  PCE 4. Give a brief account of neutral refractories.  Manufacture  Properties  Uses 5. Explain the general methods of manufacture of refractories.  Grinding  Mixing  Moulding  Drying  Firing 6. Explain any two properties of refractories.  Refractoriness  RUL  Porosity  Thermal spalling  Dimensional stability 7. Give a brief account of acidic refractories.  Manufacture  Properties  Uses 8. Give a brief account of basic refractories.  Manufacture  Properties  Uses 9. What are abrasives? How are they classified? Give two examples for each category with their important properties.  Definition  Classification  Properties with examples 10.What are the characteristics of abrasives? Explain any two properties of abrasives.Engineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 164  Characteristics  Properties 1. Hardness 2. Toughness 3. Abrasive power 11.Write short notes on synthetic abrasives.  Boron carbide or Alundum 1. Manufacture 2. Properties 3. Uses 12.Write short notes on Carborundum.  Manufacture  Properties  Uses 13. Discuss any two abrasives in detail or what are the applications of abrasives?  As loose powder  As abrasive paper or cloth  As grinding wheels 14.Write short notes on natural abrasives.  Non-siliceous abrasives 1. Diamond 2. Corundum 3. Emery  Siliceous abrasives 1. Quartz 2. Garnet 15. Discuss any four important functions of a good lubricant? Write briefly on synthetic lubricants.  Functions  Synthetic lubricants 16.What are lubricants? Discuss the classification of the lubricants.  Definition  Types 1. Liquid lubricants 2. Semi-solid lubricants 3. Solid lubricants 4. Emulsions 17. Explain the mechanism or types of lubrication?  Fluid film  Boundary lubricationEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 165  Extreme pressure lubrication 18. Explain the term; viscosity index used in lubricant technology.  Definition  Determination  Significance 19. Discuss flash point and pour point properties of lubricant?  Definition of Flash point and Pour point  Determination  Significance 20. Explain the following properties of lubricants.  Viscosity  Cloud point  Fire point  Oiliness 21.What are solid lubricants? When are they used? Explain the structure of any one solid lubricant?  Definition  Uses  Graphite or Molybdenum disulphide 22.What are greases? When are they used? Give the preparation of lithium grease.  Definition  Uses  Preparation of lithium grease 23. Name any four additives for lubricating oils? Indicate their functions.  Name of the additive  Examples  Functions 24.Write notes on petroleum oils? What are the methods to remove the impurities?  Definition  Methods 1. Removal of waxes 2. Removal of asphalt 3. Removal of sulphur 4. Removal of coloured substance 25. Explain the structures or types of CNTs.  Single-walled nanotubes  Multi-walled nanotubes 26.What are nanomaterials? Write short notes on carbon nanotubes.  DefinitionEngineering Chemistry-I Department of Chemistry, Annapoorana Engineering College, Salem 166  Carbon nanotubes 27. Explain the properties and applications of carbon nanotubes.  Properties 1. Mechanical properties 2. Electrical properties 3. Thermal properties 4. Vibrational properties 5. Kinetic properties  Applications 1. Storage devices 2. Fuel cells 3. Lithium battery 4. Protective shields 5. Sensors of gases