AQA A-level CHEMISTRY Paper 3 FINAL MARK SCHEME 2024, Exams of Chemistry

Download AQA A-level CHEMISTRY Paper 3 FINAL MARK SCHEME 2024 and more Exams Chemistry in PDF only on Docsity!

A level

AQA

A-level

CHEMISTRY

Paper 3

Mark scheme

June 2024

Version: 1 .0 Final

246A7405/3/MS

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

However, responses considered to be neutral (often prefaced by ‘Ignore’ in the mark scheme) are not penalised. 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

 Latitude should be given to the representation of C ─ C bonds in alkyl groups, given that CH 3 ─ is considered to be interchangeable with H 3 C ─ even though the latter would be preferred.  Similar^ latitude^ should^ be^ given^ to^ the^ representation^ of^ amines^ where^ NH 2 ─^ C^ will^ be allowed, although H 2 N─ C would be preferred.  Poor presentation of vertical C ─ CH 3 bonds or vertical C ─ NH 2 bonds should not be penalised. For other functional groups, such as ─ OH and ─ CN, the limit of toleranceis the half-way position between the vertical bond and the relevant atoms in the attached group.

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

3 - methyl- 2 - bromobutane should be 2 - bromo- 3 - methylbutane 2 - methylbut- 3 - ene should be 3 - methylbut- 1 - ene difluorodichloromethane should be dichlorodifluoromethane

3 3.14 Organic reaction mechanisms Curly arrows should originate either from a lone pair of electrons or from a bond. The following representations should not gain credit and will be penalised each time within a clip. H 3 C Br

_

: H C

Br H 3 C^

.Br

.. _

OH OH

For example, the following would score zero marks H H 3 C C Br HO (^) H When the curly arrow is showing the formation of a bond to an atom, the arrow can go directly to the relevant atom, alongside the relevant atom or more than half-way towards the relevant atom. In free-radical substitution  the absence of a radical dot should be penalised once only within a clip.  the use of half-headed arrows is not required, but the use of double-headed arrows or the incorrect use of half-headed arrows in free-radical mechanisms should be penalised once only within a clip The correct use of skeletal formulae in mechanisms is acceptable, but where a C-H bond breaks, both the bond and the H must be drawn to gain credit. 3.15 Extended responses For questions marked using a ‘Levels of Response’ mark scheme: Level of response mark schemes are broken down into three levels, each of which has a descriptor. Each descriptor contains two statements. The first statement is the Chemistry content statement and the second statement is the communication statement. Determining a level Start at the lowest level of the mark scheme and use it as a ladder to see whether the answer meets the Chemistry content descriptor for that level. The descriptor for the level indicates the qualities that might be seen in the student’s answer for that level. If it meets

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 answer.

**Question Answers Additional comments/Guidelines Mark

M1** skeletal formula of organic product M2 rest of equation M1 Need H on alcohol OH M1 Allow O–H for alcohol OH M2 for correct formulae for 2 - hydroxybenzenecarboxylic acid and methanol on left and H 2 O on right M2 Allow C 7 H 6 O 3 /HOC 6 H 4 COOH and CH 4 O Ignore additional non-skeletal structures for ester (assume it is working out) Allow Kekulé structures for rings

(2 x AO2) Question Answers Additional comments/Guidelines Mark 1. Ethanoic anhydride/It is less/not corrosive OR Ethanoic anhydride/It does not form strong acid/HCl /(only) forms weak/ethanoic/carboxylic acid OR Ethanoic anhydride/It is less/not vulnerable to hydrolysis Allow reverse argument for ethanoyl chloride e.g. ethanoyl chloride is (more) corrosive Ignore cost / less volatile / products are less harmful / safer / toxic / produces toxic fumes Ignore references to less/more exothermic/violent/vigorous

(1 x AO1) Question Answers Additional comments/Guidelines Mark 1.3 (nucleophilic) addition-elimination Ignore esterification / acylation

(1 x AO1)

**Question Answers Additional comments/Guidelines Mark

M**  Cross sectional (i.e. funnel top and bottom shown open)  Bung or collar drawn (with funnel spout visible through)  (Buchner/Hirsch) Funnel – approximate shape  Horizontal filter paper – allow solid or dashed line M Labels must include filter paper and indication of vacuum/water pump / reduced pressure / suction

(2 x AO3)

Question Answers Additional comments/Guidelines Mark 1. Any 2 of:  ethanoic acid  phosphoric acid  2 - hydroxybenzenecarboxylic acid  ethanoic anhydride  water Ignore catalyst / unreacted reactants Allow names or correct formulae Allow salicylic acid / 2 - hydroxybenzoic acid

(2 x AO3) **Question Answers Additional comments/Guidelines Mark

M1** Dissolve crude product in hot solvent (water and ethanol) M2 of minimum volume M3 Filter (hot to remove insoluble impurities) M4 Cool (to recrystallise) M5 Filter under reduced pressure / with Buchner/Hirsch apparatus M6 wash (with cold solvent) and dry Ignore initial filtration M1 not wrong solvent if named M2 allow reference to saturated solution as alternative to minimum volume M3 ignore method of filtration allow decant M6 allow water and/or ethanol Apply list principle for each additional process (e.g. drying agent added, base to neutralise acid added, distillation, solvent extraction) in an incorrect method Ignore reference to melting point determination

(6 x AO1)

**Question Answers Additional comments/Guidelines Mark

M1** (instead of leaving the flask open) to avoid acid/solution/liquid escaping OR to avoid (acid/solution/liquid) splashing/spraying/spitting (out) M2 (instead of inserting a bung) to allow gas/CO 2 to escape Ignore evaporation / spilling / to let gas escape / to avoid loss of product/reactant / impurities getting in Ignore pressure would build up Ignore air NOT other wrongly identified gas(es)

(2 x AO3) Question Answers Additional comments/Guidelines Mark 2. so that surface area/mass/amount stays (approx./effectively) constant Ignore concentration stays constant Ignore volume Ignore so HCl is the limiting factor Ignore so rate is only affected by [HCl] (as in Q)

(1 x AO3)

**Question Answers Additional comments/Guidelines Mark

M1** mt /mass of CO 2 produced in time t is proportional to the (amount/concentration of) HCl that has reacted (at time t ) M2 m total/total mass of CO 2 produced is proportional to the total (amount/concentration of) HCl that has reacted/was present initially (therefore mtotal – mt is proportional to (amount/conc of) HCl present at time t ) Allow ‘equal to’ / ‘represents’ for proportional to Allow mtotal is proportional to HCl ‘added’ Alternative answer: M1 mtotal – mt is equal/proportional to (mass/amount of) CO 2 still to be produced M2 (mass/amount of) CO 2 still to be produced is proportional to (amount/concentration of) HCl still to react

(2 x AO2)