GCSE Science M / Chemistry M

Transcription

1 GCSE Science M / Chemistry M Chemistry Unit MCHHP Mark scheme 4602 / 4605 January 204 Version/Stage:.0 Final Mark Scheme

2 Mark schemes are prepared by the Lead Assessment Writer and considered, together with the relevant questions, by a panel of subject teachers. This mark scheme includes any amendments made at the standardisation events which all associates participate in and is the scheme which was used by them in this examination. The standardisation process ensures that the mark scheme covers the students responses to questions and that every associate understands and applies it in the same correct way. As preparation for standardisation each associate analyses a number of students scripts: alternative answers not already covered by the mark scheme are discussed and legislated for. If, after the standardisation process, associates encounter unusual answers which have not been raised they are required to refer these to the Lead Assessment Writer. It must be stressed that a mark scheme is a working document, in many cases further developed and expanded on the basis of students reactions to a particular paper. Assumptions about future mark schemes on the basis of one year s 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 from aqa.org.uk Copyright 204 AQA and its licensors. All rights reserved. AQA retains the copyright on all its publications. However, registered schools/colleges 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 schools/colleges to photocopy any material that is acknowledged to a third party even for internal use within the centre.

3 MARK SCHEME GCSE SCIENCE M / CHEMISTRY M MCHHP JANUARY 204 Information to Examiners. 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. In a list of acceptable answers where more than one mark is available any two from is used, with the number of marks emboldened. Each of the following bullet points 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. Marking of lists This applies to questions requiring a set number of responses, but for which students 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 ) are not penalised. Example : What is the ph of an acidic solution? ( mark) Student Response Marks awarded green, red*, 5 3 red*, 8 0 3of 3

4 MARK SCHEME GCSE SCIENCE M / CHEMISTRY M MCHHP JANUARY 204 Example 2: Name two planets in the solar system. (2 marks) Student Response Marks awarded Neptune, Mars, Moon 2 Neptune, Sun, Mars, Moon Use of chemical symbols / formulae If a student 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, 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 information column or by each stage of a longer calculation. 3.4 Interpretation of it Answers using the word it should be given credit only if it is clear that the it refers 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. 3.8 Ignore / Insufficient / Do not allow Ignore or insufficient are used when the information given is irrelevant to the question or not enough to gain the marking point. Any further correct amplification could gain the marking point. Do not allow means that this is a wrong answer which, even if the correct answer is given, will still mean that the mark is not awarded. 4of 3

5 MARK SCHEME GCSE SCIENCE M / CHEMISTRY M MCHHP JANUARY 204 Quality of Written Communication and levels marking In Question 3 students are required to produce extended written material in English, and will be assessed on the quality of their written communication as well as the standard of the scientific response. Students will be required to: use good English organise information clearly use ialist vocabulary where appropriate. The following general criteria should be used to assign marks to a level: Level : Basic Knowledge of basic information Simple understanding The answer is poorly organised, with almost no ialist terms and their use demonstrating a general lack of understanding of their meaning, little or no detail The spelling, punctuation and grammar are very weak. Level 2: Clear Knowledge of accurate information Clear understanding The answer has some structure and organisation, use of ialist terms has been attempted but not always accurately, some detail is given There is reasonable accuracy in spelling, punctuation and grammar, although there may still be some errors. Level 3: Detailed Knowledge of accurate information appropriately contextualised Detailed understanding, supported by relevant evidence and examples Answer is coherent and in an organised, logical sequence, containing a wide range of appropriate or relevant ialist terms used accurately. The answer shows almost faultless spelling, punctuation and grammar. 5of 3

6 MARK SCHEME GCSE SCIENCE M / CHEMISTRY M MCHHP JANUARY 204 (a)(i) and / or eleven (protons) AO2..e (a)(ii) neutron(s) do not accept neuron / newton / nucleus (a)(iii) (group) and / or one allow alkali metals do not allow alkaline earth metals AO..c AO2..2a (b) 6 and / or six AO2 F allow f..b + g Total 6 6of 3

7 MARK SCHEME GCSE SCIENCE M / CHEMISTRY M MCHHP JANUARY 204 2(a)(i) fermentation allow ferment / fermenting AO.5.3b 2(a)(ii) carbon dioxide and / or CO 2 if formula given it must be correct do not accept CO / carbon oxide / carbon monoxide AO.5.3b 2(a)(iii) filter (to remove the yeast) or decant (the solution from the yeast) AO2.5.3b distil the solution (to separate the ethanol from the water) allow description of distillation 2(b)(i) water accept steam / water vapour allow H 2 O / hydrogen oxide AO.5.3a 2(b)(ii) this ethanol is not produced from plants or this ethanol is produced from crude oil allow biofuels are produced from plant material ignore it is not renewable / carbon neutral AO2.4.3e 2(c)(i) 5.0(4) (kj per gram) if answer given incorrect, allow correct substitution (0. x 4.2 x 2) for mark if incorrect substitution (60), allow answer correctly calculated (25.2) for mark 2 AO2.4.3b + e 2(c)(ii) the amount of energy released increases as the number of carbon atoms in the alcohol molecule increases AO3.4.3b + e 7of 3

8 MARK SCHEME GCSE SCIENCE M / CHEMISTRY M MCHHP JANUARY 204 2(c)(iii) insufficient oxygen / air (mixing with the vaporised fuel) any two from: ignore SO 2 / NO x / energy 2 AO.4.3a + e carbon monoxide carbon water 2(c)(iv) sustainable / renewable / carbon neutral alcohols with larger molecules/more carbon atoms (than ethanol) release more energy per gram ignore flammability / costs / economics / pollution / energy / biofuel ignore made from crude oil / engine modification / other uses allow plants could be used for food AO3.4.3b + e Total 4 8of 3

9 MARK SCHEME GCSE SCIENCE M / CHEMISTRY M MCHHP JANUARY Marks awarded for this answer will be determined by the Quality of Written Communication (QWC) as well as the standard of the scientific response. Examiners should also refer to the information on page 5 and apply a best-fit approach to the marking. AO d 0 marks Level ( 2 marks) Level 2 (3 4 marks) Level 3 (5 6 marks) No relevant content. There is a statement justifying the use of poly(lactic acid) bags or poly(ethene) bags. There is a comparison justifying the use of poly(lactic acid) bags or poly(ethene) bags. There are comparisons justifying the use of poly(lactic acid) bags and poly(ethene) bags examples of chemistry points made in the response: poly(lactic acid) bags are just as strong/durable as poly(ethene) bags because they can be reused poly(lactic acid) bags are, like poly(ethene) bags, able to be recycled poly(lactic acid) bags can biodegrade whereas poly(ethene) bags take many years to biodegrade poly(lactic acid) bags when disposed of in household waste will not take up space in landfill for many years whereas poly(ethene) bags will take up space in landfill for many years poly(lactic acid) bags when disposed of as litter on the land/sea will not stay for many years whereas poly(ethene) bags will stay for many years poly(lactic acid) bags are made from a sustainable/renewable resource whereas poly(ethene) bags are made from a non-renewable resource/running out poly(lactic acid) bags are made from plants that absorb/photosynthesise carbon dioxide whereas poly(ethene) bags are made from crude oil that contains locked up carbon dioxide poly(lactic acid) bags are made from an unreliable plant source unlike poly(ethene) bags poly(lactic acid) bags are made using less energy/fuels than poly(ethene) bags poly(lactic acid) bags are made using a possible food source unlike poly(ethene) bags poly(lactic acid) bags are made using a slow / batch process unlike poly(ethene) bags poly(lactic acid) bags are made using less energy/fuels than poly(ethene) bags poly(lactic acid) bags release less carbon dioxide (or contribute less to global warming) than poly(ethene) bags when made 9of 3

10 MARK SCHEME GCSE SCIENCE M / CHEMISTRY M MCHHP JANUARY 204 4(a) carbon dioxide was dissolved / absorbed by oceans / seas ignore limestone absorbed CO 2 do not allow CO 2 got trapped in limestone AO.7.2g and then marine organisms used this (dissolved carbon dioxide) to form their shells and skeletons if no other mark awarded allow one mark for carbon dioxide was locked up in limestone / carbonates / sedimentary rocks or limestone is made / formed from CO 2 4(b)(i) methane reacts / burns with oxygen (in the air) AO + 2 which releases heat / energy (for the limekiln/decomposition of limestone/calcium carbonate).4.3b 4(b)(ii) accept correct formulae AO calcium oxide products in any order..3b carbon dioxide 4(b)(iii) because nitrogen is in the air (entering the limekiln) AO + 2 and nitrogen does not react allow is not used up in the reaction(s).7.2a 4(c) CaCO 3 products can be in any order. AO2 H 2 O..3b max mark if equation is then incorrectly balanced if no other mark awarded allow calcium carbonate and water for mark Total 0 0 of 3

11 MARK SCHEME GCSE SCIENCE M / CHEMISTRY M MCHHP JANUARY 204 5(a)(i) because carbon is more reactive (than iron) it = carbon allow carbon is higher in activity series AO.3.d allow carbon displaces iron 5(a)(ii) iron oxide loses oxygen accept iron oxide reduced to iron for 2 marks AO.3.d so (iron oxide) is reduced allow carbon takes / gains oxygen 5(b) oxygen reacts / bonds with the carbon AO + 2 to produce carbon dioxide.3.2b 5(c)(i) Al and Cr AO2 correct balancing of the equation..3b 5(c)(ii) aluminium is more expensive than carbon or AO2.3.i aluminium is used which is expensive to extract because electrolysis/large amounts of energy are needed. allow aluminium is used which is expensive to extract because there are many stages in the process Total 8 of 3

12 MARK SCHEME GCSE SCIENCE M / CHEMISTRY M MCHHP JANUARY 204 6(a) although rapeseed oil has the greatest percentage / 92% / unsaturated fat or the least saturated fat (8%) ignore reference to melting points AO3.6 rapeseed oil doesn t have the greatest percentage of polyunsaturates accept sunflower oil has the greatest percentage (68%) of poly-unsaturated fat or cannot tell because polyunsaturated fats have more carbon-carbon double bonds per molecule than mono-unsaturated fats that have only one carboncarbon double bond per molecule 6(b) add single drops of bromine water (to g of oil) / measured amount allow method which adds drops of oil to bromine water AO a until the colour of the bromine water does not decolourise repeat with each of the other oils compare the results/ number of drops 6(c) oil is reacted with / added to hydrogen using a nickel catalyst ignore hydrogenated AO.6.3b at a temperature of 60 o C allow o C ignore heat/hot if neither of the condition marks are awarded, allow mark for hydrogen adding on to the double bond Total 9 2 of 3

13 MARK SCHEME GCSE SCIENCE M / CHEMISTRY M MCHHP JANUARY 204 7(a)(i) because water and carbon dioxide have boiling points greater than the average surface temperature / 78 o C accept because water and carbon dioxide are solid / liquid or do not form a gas at the average surface temperature / 78 o C AO3.7.2j 7(a)(ii) because these substances contain the elements/atoms that are in amino acids / proteins allow they thought that these substances were in the Earth s (early) atmosphere AO3.7.2e or because these substances contain the nitrogen, carbon, hydrogen and oxygen that is in amino acids 7(a)(iii) ignore lack of evidence AO ignore a long time ago.7.2d (although the Miller-Urey experiment has shown that simple amino acids can be produced) the Earth s early atmosphere may have contained different gases accept life/micro-organisms could have come from other parts of the Universe/comets. and have had different conditions or scientists have not been able to show how the simple amino acids produced the complex compounds/polypeptides/dna needed for life. 7(b) the gases are condensed or cooled to form a liquid the liquid mixture is allowed to warm up accept the liquid mixture is put into a fractionating column AO.7.2j oxygen will boil off/evaporate at a different temperature ( 83 o C) to the other gases / have different boiling points if no other mark awarded allow mark for fractional distillation Total 7 3 of 3