AQA A-level CHEMISTRY Paper 2 MARK SCHEME 2024: Organic and Physical Chemistry, Exams of Chemistry

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A level

AQA

A-level

CHEMISTRY

Paper 2 Organic and Physical Chemistry

Mark scheme

June 2024

Version: 1.0 Final

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 Examiner. 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. No student should be disadvantaged on the basis of their gender identity and/or how they refer to the gender identity of others in their exam responses. A consistent use of ‘they/them’ as a singular and pronouns beyond ‘she/her’ or ‘he/him’ will be credited in exam responses in line with existing mark scheme criteria. Further copies of this mark scheme are available from aqa.org.uk .

For example, in a question requiring 2 answers for 2 marks: Correct answers Incorrect answers (i.e. incorrect rather than neutral) Mark (2) Comment 1 0 1 1 1 1 They have not exceeded the maximum number of responses so there is no penalty. 1 2 0 They have exceeded the maximum number of responses so the extra incorrect response cancels the correct one. 2 0 2 2 1 1 2 2 0 3 0 2 The maximum mark is 2 3 1 1 The incorrect response cancels out one of the two correct responses that gained credit. 3 2 0 Two incorrect responses cancel out the two marks gained. 3 3 0 3.2 Marking procedure for calculations Full marks should be awarded for a correct numerical answer, without any working shown, unless the question states ‘Show your working’ or ‘justify your answer’. In this case, the mark scheme will clearly indicate what is required to gain full credit. If an answer to a calculation is incorrect and working is shown, process mark(s) can usually be gained by correct substitution / working and this is shown in the ‘Comments’ column or by each stage of a longer calculation. 3.3 Errors carried forward, consequential marking and arithmetic errors Allowances for errors carried forward are most likely to be restricted to calculation questions and should be shown by the abbreviation ECF or consequential in the marking scheme. An arithmetic error should be penalised for one mark only unless otherwise amplified in the marking scheme. Arithmetic errors may arise from a slip in a calculation or from an incorrect transfer of a numerical value from data given in a question. 3.4 Equations In questions requiring students to write equations, state symbols are generally ignored unless otherwise stated in the ‘Comments’ column. Examiners should also credit correct equations using multiples and fractions unless otherwise stated in the ‘Comments’ column.

3.5 Oxidation states In general, the sign for an oxidation state will be assumed to be positive unless specifically shown to be negative. 3.6 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. 3.7 Phonetic spelling The phonetic spelling of correct scientific terminology should be credited unless there is a possible confusion with another technical term or if the question requires correct IUPAC nomenclature. 3.8 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. 3.9 Ignore / Insufficient / Do not allow Ignore or insufficient is 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. 3.10 Marking crossed out work Crossed out work that has not been replaced should be marked as if it were not crossed out, if possible. Where crossed out work has been replaced, the replacement work and not the crossed out work should be marked. 3.11 Reagents The command word “Identify”, allows the student to choose to use either the name or the formula of a reagent in their answer. In some circumstances, the list principle may apply when both the name and the formula are used. Specific details will be given in mark schemes. The guiding principle is that a reagent is a chemical which can be taken out of a bottle or container. Failure to identify complete reagents will be penalised , but follow-on marks (e.g. for a subsequent equation or observation) can be scored from an incorrect attempt (possibly an incomplete reagent) at the correct reagent. Specific details will be given in mark schemes. For example, no credit would be given for  the cyanide ion or CN–^ when the reagent should be potassium cyanide or KCN;  the hydroxide ion or OH–^ when the reagent should be sodium hydroxide or NaOH;

By way of illustration, the following would apply. CH 3 C C CH 3 C CH 3 CH 2 OH C C OH

allowed allowed not allowed not allowed not allowed

NH 2 C C NH 2 NH 2 NH 2 NO 2

allowed allowed allowed allowed not allowed

CN C C CN COOH C C COOH C COOH not allowed not allowed not allowed not allowed not allowed CHO C (^) C CHO C CHO COCl C C COCl not allowed not allowed not allowed not allowed not allowed  Representation of CH 2 by CH 2 will be penalised  Some examples are given here of structures for specific compounds that should not  gain credit (but, exceptions may be made in the context of balancing equations) CH 3 COH for ethanal CH 3 CH 2 HO for ethanol OHCH 2 CH 3 for ethanol C 2 H 6 O for ethanol CH 2 CH 2 for ethene CH 2. CH 2 for ethene CH 2 : CH 2 for ethene  Each of the following should gain credit as alternatives to correct representations of the structures. CH 2 = CH 2 for ethene, H 2 C=CH 2 CH 3 CHOHCH 3 for propan- 2 - ol, CH 3 CH(OH)CH 3

 In most cases, the use of “sticks” to represent C ─ H bonds in a structure should not  be penalised. The exceptions to this when “sticks” will be penalised include  structures in mechanisms where the C ─ H bond is essential (e.g. elimination reactions in halogenoalkanes and alcohols)  when a displayed formula is required  when a skeletal structure is required or has been drawn by the candidate 3.13 Organic names As a general principle, non-IUPAC names or incorrect spelling or incomplete names should not gain credit. Some illustrations are given here. Unnecessary but not wrong numbers will not be penalised such as the number ‘2’ in 2 - methylpropane or the number ‘1’ in 2-chlorobutan- 1 - oic acid. but- 2 - ol should be butan- 2 - ol 2 - hydroxybutane should be butan- 2 - ol butane- 2 - ol should be butan- 2 - ol 2 - butanol should^ be^ butan-^2 - ol ethan-1,2-diol should be ethane-1,2-diol 2 - methpropan- 2 - ol should be 2 - methylpropan- 2 - ol 2 - methylbutan- 3 - ol should^ be^^3 - methylbutan-^2 - ol 3 - methylpentan should be 3 - methylpentane 3 - mythylpentane should be 3 - methylpentane 3 - methypentane should be 3 - methylpentane propanitrile should be propanenitrile aminethane should^ be^ ethylamine^ (although^ aminoethane^ can^ gain^ credit) 2 - methyl- 3 - bromobutane should be 2 - bromo- 3 - methylbutane 3 - bromo- 2 - methylbutane should be 2 - bromo- 3 - methylbutane 3 - methyl- 2 - bromobutane should^ be^^2 - bromo-^3 - methylbutane 2 - methylbut- 3 - ene should be 3 - methylbut- 1 - ene difluorodichloromethane should be dichlorodifluoromethane

When assigning a level you should look at the overall quality of the answer and not look to pick holes in small and specific parts of the answer where the student has not performed quite as well as the rest. If the answer covers different aspects of different levels of the mark scheme you should use a best fit approach for defining the level. Once the level has been decided, the mark within the level is determined by the communication statement:  If the answer completely matches the communication descriptor, award the higher mark within the level.  If the answer does not completely match the communication descriptor, award the lower mark within the level. The exemplar materials used during standardisation will help you to determine the appropriate level. There will be an exemplar in the standardising materials which will correspond with each level of the mark scheme and for each mark within each level. This answer will have been awarded a mark by the Lead Examiner. You can compare the student’s answer with the exemplar to determine if it is the same standard, better or worse than the example. You can then use this to allocate a mark for the answer based on the Lead Examiner’s mark on the exemplar. You may well need to read back through the answer as you apply the mark scheme to clarify points and assure yourself that the level and the mark are appropriate. Indicative content in the mark scheme is provided as a guide for examiners. It is not intended to be exhaustive and you must credit other chemically valid points. Students may not have to cover all of the points mentioned in the indicative content to reach the highest level of the mark scheme. The mark scheme will state how much chemical content is required for the highest level. An answer which contains nothing of relevance to the question must be awarded no marks. For other extended response answers: Where a mark scheme includes linkage words (such as ‘therefore’, ‘so’, ‘because’ etc), these are optional. However, a student’s marks for the question may be limited if they do not demonstrate the ability to construct and develop a sustained line of reasoning which is coherent, relevant, substantiated and logically structured. In particular answers in the form of bullet pointed lists may not be awarded full marks if there is no indication of logical flow between each point or if points are in an illogical order. The mark schemes for some questions state that the maximum mark available for an extended response answer is limited if the answer is not coherent, relevant, substantiated and logically structured. During the standardisation process, the Lead Examiner will provide marked exemplar material to demonstrate answers which have not met these criteria. You should use these exemplars as a comparison when marking student answers.

Question Answers Additional Comments/Guidelines Mark 01. Curve eg Curve with decreasing gradient 1 (1 x AO1)

Question Answers Additional Comments/Guidelines Mark 01. M1 Arrow from C–H bond to C-C M2 Arrow from C=O bond to O M3 Arrow from lone pair on O to C–O bond M4 Arrow from Br–Br bond to Br Dipoles^ must^ be^ correct^ if^ shown^ for^ M

(4 x AO2)

Question Answers Additional Comments/Guidelines Mark 01. Step 1 includes CH 3 COCH 3 and OH–^ and these are also in the rate equation Or Step 1 contains all the species in the rate equation Br 2 not in step 1 and not in rate equation so it has to be step 1 1 (1 x AO2)

Question Answers Additional Comments/Guidelines Mark 02. M1 equilibrium shifts to side with most moles M2 to oppose decrease in concentration of all reactants and products / dilution of everything OR M1 K c is expressed as a function of concentrations and concentration equals amount over volume. M2 If Volume increases the amount of R and S must increase in order to keep K c constant. Allow M2 oppose the decrease in concentration of S Kc = RS^3 /P^2 Q × 1/V (where R,S etc are amounts) So, if V increases R and S must increase relative to P and Q to keep K c constant

(2 x AO3)

Question Answers Additional Comments/Guidelines Mark 03.

M1 + 3 C 2 H 6

M2 Zeolite / Aluminosilicate / Aluminium oxide 2 (2 x AO1) Question Answers Additional Comments/Guidelines Mark 03. Option B 1 (1 x AO3) Question Answers Additional Comments/Guidelines Mark 03. Alkenes 1 (1 x AO1)

Question Answers Additional Comments/Guidelines Mark M1 CH 3 CH(OH)CH 3 + CH 3 COOH ⇌ CH 3 COOCH(CH 3 ) 2 + H 2 O O (^) O M2 Methyl ethyl ethanoate. (^) + (^) OH O +^ H^2 O 04. Allow ECF from incorrect 5 carbon ester Allow other valid names 1 - methylethyl ethanoate Isopropyl ethanoate 2 - propyl ethanoate Propan- 2 - yl ethanoate

(1 x AO1, 1 x AO2)

Question Answers Additional Comments/Guidelines Mark 04. This question is marked using Levels of Response. Refer to the Mark Scheme Instructions for Examiners for guidance. Indicative Chemistry Content Stage 1 1a Measuring cylinder(s) for the propan- 2 - ol and ethanoic acid (size not required but if specified should be between 10 - 100 cm^3 ) Allow 10cm^3 / graduated pipette or burette 1b (Dropping/teat) pipette for sulfuric acid (NOT graduated or other qualification for pipette) Stage 2 Diagram eg below to include 2a Labelled condenser shown vertical and open at top and bottom i.e. in cross section 2b Labelled water in at the bottom and water out at the top of the vertical condenser 2c Labelled reaction flask recognisable as either pear shaped or round bottomed

(6 x AO3) Level 3 5 – 6 marks All stages are virtually complete (virtually complete means one from stage 1 and two from stages 2 and 3) Answer communicates the whole explanation, including equations, coherently and shows a logical progression through all three stages Level 2 3 – 4 marks All stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies (covered means one from a stage) OR two stages virtually complete (virtually complete means one from stage 1 or two from stages 2 and 3) Answer is coherent and shows some progression through all three stages. Some steps in each stage may be incomplete Level 1 1 – 2 marks Two stages are covered (covered means one from a stage) but the explanation of each stage may be incomplete or may contain inaccuracies OR only one stage is virtually complete (virtually complete means one from stage 1 or two from stages 2 and 3) Answer shows some progression between two stages