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

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2021 AQA A-level Chemistry Paper 2 7405/2 with Answers (10 Solved Questions) - Page 1 preview image

A-levelCHEMISTRY7405/2Paper 2 Organic and Physical ChemistryMark schemeJune 2021Version 1.0: FinallOMoARcPSD|13778330

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

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2021 AQA A-level Chemistry Paper 2 7405/2 with Answers (10 Solved Questions) - Page 3 preview image

MARK SCHEME–A-LEVEL CHEMISTRY–7405/2–JUNE 20212Mark schemes are prepared by the Lead Assessment Writer and considered, together with the relevantquestions, by a panel of subject teachers. This mark scheme includes any amendments made at thestandardisation events which all associates participate in and is the scheme which was used by them inthis examination. The standardisation process ensures that the mark scheme covers the students9responses 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 students9 scripts. Alternativeanswers not already covered by the mark scheme are discussed and legislated for. If, after thestandardisation process, associates encounter unusual answers which have not been raised they arerequired to refer these to the Lead Examiner.It must be stressed that a mark scheme is a working document, in many cases further developed andexpanded on the basis of students9 reactions to a particular paper. Assumptions about future markschemes on the basis of one year9s document should be avoided; whilst the guiding principles ofassessment remain constant, details will change, depending on the content of a particular examinationpaper.Further copies of this mark scheme are available from aqa.org.uk

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MARK SCHEME–A-LEVEL CHEMISTRY–7405/2–JUNE 20213AS and A-Level ChemistryMark Scheme Instructions for Examiners1.GeneralThe 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 whatis acceptable or not worthy of credit or, in discursive answers, to give an overview of the areain which a mark or marks may be awarded.The extra information in the 8Comments9 column 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.You should mark according to the contents of the mark scheme. If you are in any doubt aboutapplying 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: whereconsequential marking needs to be considered in a calculation; or the answer may be on thediagram 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 whichmight confuse the main part of the mark scheme yet may be helpful in ensuring that marking isstraightforward and consistent.The use of M1, M2, M3 etc in the right-hand column refers to the marking points in the order inwhich they appear in the mark scheme. So, M1 refers to the first marking point, M2 the secondmarking point etc.2.Emboldening2.1In a list of acceptable answers where more than one mark is available 8anytwofrom9 isused, with the number of marks emboldened. Each of the following bullet points is apotential mark.2.2A boldandis used to indicate that both parts of the answer are required to award themark.2.3Alternative answers acceptable for a mark are indicated by the use ofOR. Different termsin the mark scheme are shown by a / ; eg allow smooth / free movement.3.Marking points3.1Marking of listsThis applies to questions requiring a set number of responses, but for which studentshave provided extra responses. The general8List9principle to be followed in such asituation 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, nomarks can be awarded.However, responses considered to be neutral (often prefaced by 8Ignore9 in the markscheme) are not penalised.

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MARK SCHEME–A-LEVEL CHEMISTRY–7405/2–JUNE 20214For example, in a question requiring 2 answers for 2 marks:CorrectanswersIncorrectanswers (i.e.incorrect ratherthan neutral)Mark (2)Comment101111They have not exceeded the maximumnumber of responses so there is nopenalty.120They have exceeded the maximum numberof responses so the extra incorrectresponse cancels the correct one.202211220302The maximum mark is 2311The incorrect response cancels out one ofthe two correct responses that gainedcredit.320Two incorrect responses cancel out the twomarks gained.3303.2Marking procedure for calculationsFull marks should be awarded for a correct numerical answer, without any workingshown, unless the question states 8Show your working9 or 8justify your answer9. In thiscase, 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) canusually be gained by correct substitution / working and this is shown in the 8Comments9column or by each stage of a longer calculation.3.3Errors carried forward, consequential marking and arithmetic errorsAllowances for errors carried forward are most likely to be restricted to calculationquestions and should be shown by the abbreviation ECF or consequential in the markingscheme.An arithmetic error should be penalised for one mark only unless otherwise amplified inthe marking scheme. Arithmetic errors may arise from a slip in a calculation or from anincorrect transfer of a numerical value from data given in a question.3.4EquationsIn questions requiring students to write equations, state symbols are generally ignoredunless otherwise stated in the 8Comments9 column.Examiners should also credit correct equations using multiples and fractions unlessotherwise stated in the 8Comments9 column.

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MARK SCHEME–A-LEVEL CHEMISTRY–7405/2–JUNE 202153.5Oxidation statesIn general, the sign for an oxidation state will be assumed to be positive unlessspecifically shown to be negative.3.6Interpretation of 8it9Answers using the word 8it9 should be given creditonly if it is clear that the 8it9 refers to thecorrect subject.3.7Phonetic spellingThe phonetic spelling of correct scientific terminology should be creditedunlessthere is apossible confusion with another technical term or if the question requires correct IUPACnomenclature.3.8Brackets(…..) are used to indicate information which is not essential for the mark to be awardedbut is included to help the examiner identify the sense of the answer required.3.9Ignore / Insufficient / Do not allowIgnore or insufficient is used when the information given is irrelevant to the question or notenough to gain the marking point. Any further correct amplification could gain the markingpoint.Donotallow means that this is a wrong answer which, even if the correct answer isgiven, will still mean that the mark is not awarded.3.10Marking crossed out workCrossed out work thathas not beenreplaced should be marked as if it were not crossedout, if possible. Where crossed out workhas beenreplaced, the replacement work andnot the crossed out work should be marked.3.11ReagentsThe command word <Identify=, allows the student to choose to useeitherthe name or theformula of a reagent in their answer. In some circumstances, the list principle may applywhen both the name and the formula are used. Specific details will be given in markschemes.The guiding principle is that a reagent is a chemical which can be taken out of a bottle orcontainer. Failure to identify complete reagentswill 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 inmark schemes.For example,no creditwould 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 20216•the Ag(NH3)2+ion when the reagent should be Tollens9 reagent (or ammoniacal silvernitrate). In this example, no credit is given for the ion, but credit could be given for acorrect observation following on from the use of the ion. Specific details will be given inmark schemes.In the event that a student provides, for example,bothKCN and cyanide ion, it would beusual to ignore the reference to the cyanide ion (because this is not contradictory) andcredit the KCN. Specific details will be given in mark schemes.3.12Organic structuresWhere students are asked to draw organic structures, unless a specific type is required inthe question and stated in the mark scheme, these may be given as displayed, structuralor 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, butneed not show correct bond angles.•Skeletal formulae must show carbon atoms by an angle or suitable intersection in theskeleton chain. Functional groups must be shown and it is essential that all atoms otherthan C atoms are shown in these (except H atoms in the functional groups ofaldehydes, secondary amines and N-substituted amides which do not need to beshown).•Structures must not be ambiguous, e.g. 1-bromopropane should be shown asCH3CH2CH2Br and not as the molecular formula C3H7Br which could also represent theisomeric 2-bromopropane.•Bonds should be drawn correctly between the relevant atoms. This principle applies inall 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 clearlyshown. Wrongly bonded atoms will be penalisedon every occasion. (see theexamples below)•The same principle should also be applied to the structure of alcohols.For example, ifstudents show the alcohol functional group as C ─ HO, they should be penalisedonevery occasion.•Latitude should be given to the representation of C ─ C bonds in alkyl groups, giventhat CH3─is considered to be interchangeable with H3C─even though the latterwould be preferred.•Similar latitude should be given to the representation of amines where NH2─ C will beallowed, although H2N─ C would be preferred.•Poor presentation of vertical C ─ CH3bonds or vertical C ─ NH2bonds shouldnotbepenalised. 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 theattached group.lOMoARcPSD|13778330

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MARK SCHEME–A-LEVEL CHEMISTRY–7405/2–JUNE 20217By way of illustration, the following would apply.CH3CCCH3CCH3CH2OHCCOHallowedallowednot allowednot allowednot allowedNH2CCNH2NH2NH2NO2allowedallowedallowedallowednot allowedCNCCCNCOOHCCCOOHCCOOHnot allowednot allowednot allowednot allowednot allowedCHOCCCHOCCHOCOClCCCOClnot allowednot allowednot allowednot allowednot allowed•Representation of CH2by C−H2will be penalised•Some examples are given here ofstructuresfor specific compounds that shouldnotgain credit (but, exceptions may be made in the context of balancing equations)CH3COHforethanalCH3CH2HOforethanolOHCH2CH3forethanolC2H6OforethanolCH2CH2foretheneCH2.CH2foretheneCH2:CH2forethene•Each of the followingshould gain creditas alternatives to correct representations ofthe structures.CH2= CH2forethene,H2C=CH2CH3CHOHCH3forpropan-2-ol, CH3CH(OH)CH3

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MARK SCHEME–A-LEVEL CHEMISTRY–7405/2–JUNE 20218•In most cases, the use of <sticks= to represent C ─ H bonds in a structure shouldnotbe penalised. The exceptions to this when <sticks= will be penalised include•structures in mechanisms wherethe C ─ H bond is essential (e.g. eliminationreactions in halogenoalkanes and alcohols)•when a displayed formula is required•when a skeletal structure is required or has been drawn by the candidate3.13Organic namesAs a general principle, non-IUPAC names or incorrect spelling or incomplete namesshouldnotgain credit. Some illustrations are given here.Unnecessary but not wrong numbers willnotbe penalised such as the number 829 in 2-methylpropane or the number 819 in 2-chlorobutan-1-oic acid.but-2-olshould bebutan-2-ol2-hydroxybutaneshould bebutan-2-olbutane-2-olshould bebutan-2-ol2-butanolshould bebutan-2-olethan-1,2-diolshould beethane-1,2-diol2-methpropan-2-olshould be2-methylpropan-2-ol2-methylbutan-3-olshould be3-methylbutan-2-ol3-methylpentanshould be3-methylpentane3-mythylpentaneshould be3-methylpentane3-methypentaneshould be3-methylpentanepropanitrileshould bepropanenitrileaminethaneshould beethylamine(although aminoethane can gain credit)2-methyl-3-bromobutaneshould be2-bromo-3-methylbutane3-bromo-2-methylbutaneshould be2-bromo-3-methylbutane3-methyl-2-bromobutaneshould be2-bromo-3-methylbutane2-methylbut-3-eneshould be3-methylbut-1-enedifluorodichloromethaneshould bedichlorodifluoromethanelOMoARcPSD|13778330

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