Redox titrations for A2 chemistry

Mathsandscience.net Question on redox titrations. Interesting notes Fe(II) will go to Fe(III) this is usually titrated against KMnO4 which is a 5 Fe to one KMnO4 (MnO4-if you prefer) H202 is an interesting one H202 gO2 + 2H+ + 2e the reaction below can be used to work out the amount of iodine in a solution 2S2O32-+ I2 g 2I-+ S4O62-BUT WHY!!! Add iodine to a solution containing lets say ClO-ions which acts as an oxidising agent producing iodine ( dark colour) then titrate a known amount against thiosulphate ions to work out how much iodine and hence ClO-concentration!! These equations help ClO-+ 2I-+2H+ gCl-+ I2 +H202 2Cu2+ + 4I-gI2 + 2CuI Copper (II) reduced to copper(I) ions To watch the free video lesson on the solutions click http://www.mathsandscience.net/Problem 1 25 cm3 of an iron (II) salt required 23.5 cm3 of 0.0200 mol dm-3 pottasium manganate(VII) ions for complete oxidation in acid solution. Calculate the concentration in mol dm-3 of fe2+ ions in the solution that was titrated Problem 2 2.04 g of hydrated iron(II) sulphate crystals were dissolved in 50 cm3 of sulphuric acid. The solution was poured into 250cm3 conical flask made up to the mark with distilled water. 25 cm3 of this solution was titrated with 0.0100 mol dm-3 potassium manganate(VII) solution. 24 cm 3 of MnO4-was used. Determine the formula of the hydrated crystals. Copyright 2010 Fiaraz IqbalMathsandscience.net Problem 3 A multi vitamin tablet contain vitamins and iron. 0.325g was dissolved in water and a small amount of dilute sulphuric acid was added. 12.10 cm3 of 0.002 mol dm-3 of potassium manganate (VII) solution was titrated until a permanent pink colour was observed. Calculate the percentage mass of iron in the tablets. Problem 4 25 cm3 of hydrogen peroxide was poured in to 250 cm3 volumetric flask and made up to the mark with distilled water, 25 cm3 of this solution was titrated against 0.02 mol dm-3 of potassium manganate (VII) solution., 34.6cm3 of MnO4-was required for complete oxidation. H202 gO2 + 2H+ + 2e calculate the concentration of H202 Problem 5 30 cm3 of bleach was added in excess of Iodide ions in dilute sulphuric acid. ClO-+ 2I-+2H+ gCl-+ I2 +H202 the iodine formed was titrated against 0.2 mol dm-3 sodium thiosulphate solution. 28.63cm3 was needed you might need this! 2S2O32-+ I2 g 2I-+ S4O62-Problem 6 A 0.6 sample of bronze is reacted with nitric acid creating copper(II) ions. The solution was neutralised and reeacted with iodide ions. Titration against 0.2 mols dm-3 of sodium thiosulphate required 21.9 cm3 calculate the percentage of copper in the bronze. Copyright 2010 Fiaraz IqbalMathsandscience.net Answers Problem 1 0.094 mol dm-3 problem 2 FeSO4 7 H20 problem 3 2.08% problem 4 0.692 mol dm-3 problem 5 0.0955 mol dm-3 Problem 6 46.4% Copyright 2010 Fiaraz Iqbal