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2021 AQA A-level Chemistry Paper 2 7405/2 with Answers (10 Solved Questions)

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    A-level CHEMISTRY 7405/2 Paper 2 Organic and Physical Chemistry Mark scheme June 2021 Version 1.0: Final lOMoARcPSD|13778330

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    MARK SCHEME – A-LEVEL CHEMISTRY – 7405/2 – JUNE 2021 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 students9 responses to questions and that every associate understands and applies it in the same correct way. As preparation for standardisati on each associate analyses a number of students9 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 students9 reactions to a particular paper. Assumptions about future mark schemes on the basis of one year9s 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

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    MARK SCHEME – A-LEVEL CHEMISTRY – 7405/2 – JUNE 2021 3 AS and A-Level Chemistry Mark Scheme Instructions for 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 in the 8Comments9 column is aligne d 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. You should mark according to the contents of the mark scheme. If you are in any doubt about applying the mark scheme to a particular response, consult your Team Leader. 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 might confuse the main part of the mark scheme yet may be helpful in ensuring that marking is straightforward and consistent. The use of M1, M2, M3 etc in the right-hand column refers to the marking points in the order in which they appear in the mark scheme. So, M1 refers to the first marking point, M2 the second marking point etc. 2. Emboldening 2.1 In a list of acceptable answers where more than one m ark is available 8any two from9 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 3.1 Marking of lists This applies to questions requiring a set number of responses, but for which students have provided extra responses. The general 8List9 principle to be followed in such a situation is that 8right + wrong = wrong9. 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 (often prefaced by 8Ignore9 in the mark scheme) are not penalised.

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    MARK SCHEME – A-LEVEL CHEMISTRY – 7405/2 – JUNE 2021 4 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 8Show your working9 or 8justify your answer9. 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 8Comments9 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 8Comments9 column. Examiners should also credit correct equations using multiples and fractions unless otherw ise stated in the 8Comments9 column.

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    MARK SCHEME – A-LEVEL CHEMISTRY – 7405/2 – JUNE 2021 5 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 8it9 Answers using the word 8it9 should be given credit only if it is clear that the 8it9 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;

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    MARK SCHEME – A-LEVEL CHEMISTRY – 7405/2 – JUNE 2021 6 • the Ag(NH 3 ) 2 + ion when the reagent should be Tollens9 reagent (or ammoniacal silver nitrate). In this example, no credit is given for the ion, but credit could be given for a correct observation following on from the use of the ion. Specific details will be given in mark schemes. In the event that a student provides, for example, both KCN and cyanide ion, it would be usual to ignore the reference to the cyanide ion (because this is not contradictory) and credit the KCN. Specific details will be given in mark schemes. 3.12 Organic structures Where students are asked to draw organic structures, unless a specific type is required in the question and stated in the mark scheme, these may be given as displayed, structural or skeletal formulas or a combination of all three as long as the result is unambiguous. In general • Displayed formulae must show all of the bonds and all of the atoms in the molecule, but need not show correct bond angles. • Skeletal formulae must show carbon atoms by an angle or suitable intersection in the skeleton chain. Functional groups must be shown and it is essential that all atoms other than C atoms are shown in these (except H atoms in the functional groups of aldehydes, secondary amines and N-substituted amides which do not need to be shown). • Structures must not be ambiguous, e.g. 1-bromopropane should be shown as CH 3 CH 2 CH 2 Br and not as the molecular formula C 3 H 7 Br which could also represent the isomeric 2-bromopropane. • Bonds should be drawn correctly between the relevant atoms. This principle applies in all cases where the attached functional group contains a carbon atom, e.g nitrile, carboxylic acid, aldehyde and acid chloride. The carbon-carbon bond should be clearly shown. Wrongly bonded atoms will be penalised on every occasion . (see the examples below) • The same principle should also be applied to the structure of alcohols. For example, if students show the alcohol functional group as C ─ HO, they should be pen alised on every occasion . • 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 tole rance is the half-way position between the vertical bond and the relevant atoms in the attached group. lOMoARcPSD|13778330

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    MARK SCHEME – A-LEVEL CHEMISTRY – 7405/2 – JUNE 2021 7 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

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    MARK SCHEME – A-LEVEL CHEMISTRY – 7405/2 – JUNE 2021 8 • 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 829 in 2 - methylpropane or the number 819 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 lOMoARcPSD|13778330

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