GCSE Science Chemistry June 2008 3F Paper Ans Key

Version 1.0: 0608 abc General Certificate of Secondary Education Chemistry 4421 CHY3F Unit 3 Chemistry Mark Scheme 2008 examination June series Mark schemes are prepared by the Principal Examiner and considered, together with the relevant questions, by a panel of subject teachers. This mark scheme includes any amendments made at the standardisation meeting attended by all examiners and is the scheme which was used by them in this examination. The standardisation meeting ensures that the mark scheme covers the candidatesresponses to questions and that every examiner understands and applies it in the same correct way. As preparation for the standardisation meeting each examiner analyses a number of candidatesscripts: alternative answers not already covered by the mark scheme are discussed at the meeting and legislated for. If, after this meeting, examiners encounter unusual answers which have not been discussed at the meeting they are required to refer these to the Principal Examiner. It must be stressed that a mark scheme is a working document, in many cases further developed and expanded on the basis of candidatesreactions to a particular paper. Assumptions about future mark schemes on the basis of one years document should be avoided; whilst the guiding principles of assessment remain constant, details will change, depending on the content of a particular examination paper. Further copies of this Mark Scheme are available to download from the AQA Website: www.aqa.org.uk Copyright © 2008 AQA and its licensors. All rights reserved. COPYRIGHT AQA retains the copyright on all its publications. However, registered centres for AQA are permitted to copy material from this booklet for their own internal use, with the following important exception: AQA cannot give permission to centres to photocopy any material that is acknowledged to a third party even for internal use within the centre. Set and published by the Assessment and Qualifications Alliance. The Assessment and Qualifications Alliance (AQA) is a company limited by guarantee registered in England and Wales (company number 3644723) and a registered charity (registered charity number 1073334). Registered address: AQA, Devas Street, Manchester M15 6EX Dr Michael Cresswell Director GeneralChemistry CHY3F AQA GCSE Mark Scheme 2008 June Series 3 MARK SCHEME Information to Examiners 1. General The mark scheme for each question shows: • the marks available for each part of the question • the total marks available for the question • the typical answer or answers which are expected • extra information to help the Examiner make his or her judgement and help to delineate what is acceptable or not worthy of credit or, in discursive answers, to give an overview of the area in which a mark or marks may be awarded. The extra information is aligned to the appropriate answer in the left-hand part of the mark scheme and should only be applied to that item in the mark scheme. At the beginning of a part of a question a reminder may be given, for example: where consequential marking needs to be considered in a calculation; or the answer may be on the diagram or at a different place on the script. In general the right hand side of the mark scheme is there to provide those extra details which confuse the main part of the mark scheme yet may be helpful in ensuring that marking is straightforward and consistent. 2. Emboldening 2.1 In a list of acceptable answers where more than one mark is available any two fromis used, with the number of marks emboldened. Each of the following lines is a potential mark. 2.2 A bold and is used to indicate that both parts of the answer are required to award the mark. 2.3 Alternative answers acceptable for a mark are indicated by the use of or. (Different terms in the mark scheme are shown by a /; eg allow smooth /free movement.) 3. Marking points 3.1 Marking of lists This applies to questions requiring a set number of responses, but for which candidates have provided extra responses. The general principle to be followed in such a situation is that right + wrong = wrong. Each error/contradiction negates each correct response. So, if the number of error/contradictions equals or exceeds the number of marks available for the question, no marks can be awarded. However, responses considered to be neutral (indicated as * in example 1) are not penalised. Chemistry CHY3F AQA GCSE Mark Scheme 2008 June Series 4 Example 1: What is the pH of an acidic solution? (1 mark) Candidate Response Marks awarded 1 4,8 0 2 green, 5 0 3 red*, 5 1 4 red*, 8 0 Example 2: Name two planets in the solar system. (2 marks) Candidate Response Marks awarded 1 Pluto, Mars, Moon 1 2 Pluto, Sun, Mars, Moon 0 3.2 Use of chemical symbols /formulae If a candidate writes a chemical symbol /formula instead of a required chemical name, full credit can be given if the symbol /formula is correct and if, in the context of the question, such action is appropriate. 3.3 Marking procedure for calculations Full marks can be given for a correct numerical answer, as shown in the column answers, without any working shown. However if the answer is incorrect, mark(s) can be gained by correct substitution /working and this is shown in the extra informationcolumn; 3.4 Interpretation of itAnswers using the word itshould be given credit only if it is clear that the itrefers to the correct subject. 3.5 Errors carried forward Any error in the answers to a structured question should be penalised once only. Papers should be constructed in such a way that the number of times errors can be carried forward are kept to a minimum. Allowances for errors carried forward are most likely to be restricted to calculation questions and should be shown by the abbreviation e.c.f. in the marking scheme. 3.6 Phonetic spelling The phonetic spelling of correct scientific terminology should be credited unless there is a possible confusion with another technical term. 3.7 Brackets (..) are used to indicate information which is not essential for the mark to be awarded but is included to help the examiner identify the sense of the answer required. Chemistry CHY3F AQA GCSE Mark Scheme 2008 June Series 5 COMPONENT NUMBER: CHY3F COMPONENT NAME: Chemistry STATUS: Final DATE: June 2008 question answers extra information mark 1(a)(i) 27.0 25.9 or 25.9 27.0 or 1.1 1 1(a)(ii) C 1 1(b)(i) will damage /destroy /dissolve /corrode /erode the coin accept coin will lose its value ignore burns the coin 1 1(b)(ii) only a very small amount is used or accurate /sensitive /rapid method allow quick /easy /precise /reliable allow doesnt damage the coin or coin doesnt lose value or coin doesnt lose any silver ignore safe 1 Total 4 Chemistry CHY3F AQA GCSE Mark Scheme 2008 June Series 6 COMPONENT NUMBER: CHY3F COMPONENT NAME: Chemistry STATUS: Final DATE: June 2008 question answers extra information mark 2(a)(i) floated /(moved on) surface accept does not sink ignore it melted 1 2(a)(ii) melted /molten ignore heat is given off 1 2(a)(iii) hydrogen allow H2 1 2(b)(i) potassium /rubidium /caesium /francium accept: K /Rb /Cs /Fr 1 2(b)(ii) they are metals they form ions with a 1+ charge 1 1 2(c)(i) atomic weight 1 2(c)(ii) similar 1 2(c)(iii) groups 1 2(d) left gaps owtte 1 Total 10 Chemistry CHY3F AQA GCSE Mark Scheme 2008 June Series 7 COMPONENT NUMBER: CHY3F COMPONENT NAME: Chemistry STATUS: Final DATE: June 2008 question answers extra information mark 3(a)(i) (hydrochloric) acid carbon dioxide limewater 1 1 1 3(a)(ii) sodium hydroxide ammonia litmus 1 1 1 3(b) no distinctive colour (flame) owtte allow: not a metal (ion) accept flame tests only identify single elements 1 Total 7 Chemistry CHY3F AQA GCSE Mark Scheme 2008 June Series 8 COMPONENT NUMBER: CHY3F COMPONENT NAME: Chemistry STATUS: Final DATE: June 2008 question answers extra information mark 4(a)(i) fats 1 4(a)(ii) 100 accept 4 ×25 1 4(a)(iii) kilojoules 1 4(b)(i) chips contain fat /oil fat /oil has high energy content 1 1 4(b)(ii) (could lead to) obesity /high cholesterol /heart disease /clogs arteries allow gains weight etc. ignore any reference to fat ignore veins 1 Total 6 Chemistry CHY3F AQA GCSE Mark Scheme 2008 June Series 9 COMPONENT NUMBER: CHY3F COMPONENT NAME: Chemistry STATUS: Final DATE: June 2008 question answers extra information mark 5(a) contains (large amounts of) dissolved solids /difficult to remove dissolved solids allow salty /too much salt allow sea water makes you thirsty /vomit allow polluted /untreated /contaminated 1 5(b) filtered: removes solids /removes insoluble material /dirt chlorine: kills/destroy bacteria/microbes/germs etc ignore large objects allow disinfect /sterilise or gets rid of bacteria ignore purify /clean 1 1 Total 3 Chemistry CHY3F AQA GCSE Mark Scheme 2008 June Series 10 COMPONENT NUMBER: CHY3F COMPONENT NAME: Chemistry STATUS: Final DATE: June 2008 question answers extra information mark 6(a)(i) hydrogen /H+ /H+ (aq) allow H3O+ (aq) ignore H alone 1 6(a)(ii) any valid test linked comparison eg magnesium or any (named) carbonate any one from: • weak(er) acid: slower rate /fewer bubbles or less gas • weak(er) acid longer for Mg to disappear or UI or pH paper /solution /meter /full range indicator (1) any one from: (1) • weak(er) acid has higher pH • correct comparison of colours or conductivity test (1) weak acid conducts less or bulb (1) less bright NB titration = 0 allow zinc /iron do not allow calcium or alkali metals independent mark allow converse for strong(er) not litmus or any other paper independent mark allow converse for strong(er) acid pH values must be below 7 ie strong = red /pink weak = orange /yellow allow converse for stronger 1 1 Question 6 continued on next page... Chemistry CHY3F AQA GCSE Mark Scheme 2008 June Series 11 COMPONENT NUMBER: CHY3F COMPONENT NAME: Chemistry STATUS: Final DATE: June 2008 Question 6 continued... question answers extra information mark 6(b)(i) any two from eg: • nicotine kills people • nicotine causes cancer /diseases • nicotine is harmful /dangerous • nicotine is addictive • cost to NHS any plausible answer allow it would save lives allow it kills people ignore references to pollution /passive smoking 2 6(b)(ii) any two from eg: • nicotinic acid /vitamin B3 /niacin has different properties to nicotine • it is in many /listed foods or nicotine in food is not dangerous • more health risks to people /pellagra /diarrhoea /dermatitis /dementia /it will cause deaths or save lives • it is a vitamin or important part of diet • tobacco raises money /taxes • human rights issues • cant give up straight away /are addicted to it or perceived benefit of smoking any sensible answer ignore if you ban nicotine, nicotinic acid cannot be made ignore malnutrition ignore just illness2 Total 7 Chemistry CHY3F AQA GCSE Mark Scheme 2008 June Series 12 COMPONENT NUMBER: CHY3F COMPONENT NAME: Chemistry STATUS: Final DATE: June 2008 question answers extra information mark 7(a) reasonable smooth curve do not allow straight lines joining dot to dot curve must extend from 0 and 30 oC 1 7(b) solubility curve changes direction allow solubility decreases (after 35 oC) or solubility goes up and down 1 7(c) (experiments were) repeated allow they were an average 1 7(d) 35 accept any value from 34 to 35 1 7(e) 14 accept any value from 13 to 15 1 7(f) 27 correct answer = 2 marks accept 46 or 19 for 1 mark 2 7(g) no more solid /gas can be dissolved owtte allow unable to dissolve any more or no more can go into solution ignore absorbs 1 Total 8