AQA A-level CHEMISTRY 7405-1 Paper 1 Inorganic and Physical Chemistry Mark scheme June 2023, Exams for Chemistry

AQA A-level CHEMISTRY 7405-1 Paper 1 Inorganic and Physical Chemistry Mark scheme June 2023 Exams for Chemistry 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. Further copies of this mark scheme are available from MARK SCHEME – A-LEVEL CHEMISTRY – 7405/1 – JUNE 2023 Exams for Chemistry 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 „Comments‟ 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 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 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. A bold and is used to indicate that both parts of the answer are required to award the mark. Alternative answers acceptable for a mark are indicated by the use of OR. Different terms ithkhhb/llth/ft AQA A-level CHEMISTRY 7405-1 Paper 1 Inorganic and Physical Chemistry Mark scheme June 2023 Exams for Chemistry For example, in a question requiring 2 answers for 2 marks: Correct answers Incorrect answers (ie 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 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. MARK SCHEME – A-LEVEL CHEMISTRY – 7405/1 – JUNE 2023 Exams for Chemistry Examiners should also credit correct equations using multiples and fractions unless otherwise stated in the „Comments‟ column. Oxidation states In general, the sign for an oxidation state will be assumed to be positive unless specifically shown to be negative. 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. 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. 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. 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. 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. AQA A-level CHEMISTRY 7405-1 Paper 1 Inorganic and Physical Chemistry Mark scheme June 2023 Exams for Chemistry 3 2  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;  the Ag(NH ) + ion when the reagent should be Tollens‟ 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. 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 CH3CH2CH2Br and not as the molecular formula C3H7Br 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, eg 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 penalised on every occasion.  Latitude should be given to the representation of C ─ C bonds in alkyl groups, given MARK SCHEME – A-LEVEL CHEMISTRY – 7405/1 – JUNE 2023 Exams for Chemistry By way of illustration, the following would apply. CH3 C C CH 3 C CH3CH2 OH C C OH allowed allowed not allowed not allowed not allowed NH2 C C NH2 NH2 NH2 NO2 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 CH2 by CH2 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) CH3COH for ethanal AQA A-level CHEMISTRY 7405-1 Paper 1 Inorganic and Physical Chemistry Mark scheme June 2023 Exams for Chemistry CH3CHOHCH3 for propan-2-ol, CH3CH(OH)CH3 MARK SCHEME – A-LEVEL CHEMISTRY – 7405/1 – JUNE 2023 Exams for Chemistry  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 (eg 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. 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 MARK SCHEME – A-LEVEL CHEMISTRY – 7405/1 – JUNE 2020 3 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. H3C Br _ : H C . Br H3C . .Br .. _ OH OH For example, the following would score zero marks H H3C 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. Extended responses For questions marked using a ‘Levels of Response’ mark scheme: MARK SCHEME – A-LEVEL CHEMISTRY – 7405/1 – JUNE 2020 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 MARK SCHEME – A-LEVEL CHEMISTRY – 7405/1 – JUNE 2020 BaCl2 –3889 01.2 MgO –2493 MgCl2 –2018 Question Answers Additional comments/Guidelines Mark M1 ΔfH = ΔaH (Sr) + 2ΔaH (Cl) + Δ1st IEH (Sr) + Δ2nd IEH (Sr) + 2ΔEAH (Cl) + ΔLEH (Sr) 1 Or – 828 = 164 + (2 x 121) + 548 + 1060 + (2 x ΔEAH) + (– 2112) 01.1 M2 2 x ΔEAH = – 730 1 M3 ΔEAH = – 365 (kJ mol–1 ) Allow M3 = M2÷2 (+) 365, –304.5, and –730 = 2 marks 1 (+) 304.5, (+) 730 and –609 = 1 mark (+) 609 = 0 marks 11 1 All three lines must be show