Organic chemistry questions

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• AQA 7405 · June 2025 · Paper 2 · Q1 · 12 marks

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  [1.4] Students had to recognize that reaction 2 was an elimination reaction and give a suitable reagent and condition for this. Lots were able to suggest a strong alkali and give hot ethanolic as the conditions. The most common errors were in suggesting aqueous conditions.

  Text version

  This question is about different ways to make 1,2-dichlorobutane. Reaction 1 converts 2-chlorobutane, CH3CH2CHClCH3, into 1,2-dichlorobutane, CH3CH2CHClCH2Cl. Reaction 2 converts 2-chlorobutane into but-1-ene, CH3CH2CH=CH2. Reaction 3 converts but-1-ene into 1,2-dichlorobutane.

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• AQA 7405 · June 2025 · Paper 2 · Q2 · 7 marks

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  [2.1] The requirement to include Z- before the rest of the name of the geometric isomer given was often missed, but students were much better at explaining the reason why geometric isomers exist. Students who did not score the final mark were often imprecise in their use of language to describe the requirement for both carbon atoms in the C=C double bond to be attached to two different groups.

  Text version

  This question is about isomerism. Compound L has a C=C bond. The left alkene carbon is bonded to H above and CH3 below; the right alkene carbon is bonded to CH3 above and CH2CH3 below.

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• AQA 7405 · June 2025 · Paper 2 · Q3 · 20 marks

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  [3.6] Students were given data about the mass of plasticiser absorbed by foods with different fat and water contents. Many could see the link between the amount of fat and the amount of plasticiser but far fewer were able identify that both fats and the plasiciser are non-polar and so form van der Waals’ forces between the molecules. The most common error was to focus on the ester links and state that the plasticiser was polar, or to say that hydrogen bonding between fat and plasiciser was the intermolecular force responsible for the trend shown.

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  This question is about polymers.

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• AQA 7405 · June 2025 · Paper 2 · Q5 · 11 marks

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  [5.1] Students were quite good at showing the formula of TNT having been given its IUPAC name but far fewer could balance the equation with 3HNO3 on the reactants side and 3H2O on the products side.

  Text version

  This question is about making 2-methyl-1,3,5-trinitrobenzene (TNT). TNT is made by reacting methylbenzene with concentrated nitric acid in the presence of concentrated sulfuric acid.

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• AQA 7405 · June 2025 · Paper 2 · Q6 · 5 marks

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  [6.1] Students were required to deduce why D2O is used instead of CCl4 or H2O when obtaining a 1H NMR spectrum for lysine. Many were able to score here for relating the polar nature of the lysine to the fact that would not dissolve well in non-polar CCl4 or that D2O does not give its own signal in a 1H NMR spectrum.

  Text version

  GHK is a natural tripeptide in human blood plasma with amino-acid sequence Lys-His-Gly. Glycine is H2NCH2COOH.

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• AQA 7405 · June 2025 · Paper 2 · Q8 · 13 marks

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  [8.3] This question was well answered and students were often able to give prevention of loss of volatile liquid as a the reason a cap on the hypodermic syringe will improve the experiment.

  Text version

  This question is about gas volumes. To determine Mr of volatile liquid Y, a student records the initial air volume in a gas syringe, weighs a hypodermic syringe containing Y, injects a small amount through a rubber cap into the gas syringe in an oven, reweighs the hypodermic syringe, and records final gas volume, oven temperature and atmospheric pressure. Results: initial air volume 5 cm^3; mass syringe + Y before injection 3.873 g; mass after injection 3.471 g; final gas volume 110 cm^3; temperature 155 degC; pressure 101 kPa.

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• AQA 7405 · June 2025 · Paper 2 · Q9 · 11 marks

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  [9.3] This question was well answered with students being able to show they could manipulate the appropriate temperature data given to calculate 1 𝑇𝑇 in K-1 Those who got this wrong had often rounded incorrectly.

  Text version

  This question is about rates of reaction. To investigate bromoalkane hydrolysis, a cross is drawn on a boiling tube. Aqueous silver nitrate is added to ethanolic RBr in the tube in a warm water bath, and the time for the cross to become invisible is recorded. The method is repeated at different temperatures.

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• AQA 7405 · June 2025 · Paper 3 · Q5 · 10 marks

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  [5.2] The drawing of apparatus diagrams continues to be a skill that needs more practice although most students did attempt a cross-sectional line diagram. The inclusion of a thermometer is a mistake in a reflux apparatus, and this cost many students M2.

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  This question is about oxidation.

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• AQA 7405 · June 2024 · Paper 2 · Q1 · 11 marks

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  [1.3] This unfamiliar mechanism question was well answered and discriminated well. The best students were able to deduce the correct curly arrows from the information given.

  Text version

  Propanone reacts with bromine in alkaline conditions: CH3COCH3 + Br2 + OH^- -> CH3COCH2Br + Br^- + H2O. The rate equation is rate = k[CH3COCH3][OH^-].

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• AQA 7405 · June 2024 · Paper 2 · Q3 · 10 marks

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  [3.3] This was well known and over 70% scored the mark for alkenes.

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  This question is about hydrocarbons.

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• AQA 7405 · June 2024 · Paper 2 · Q5 · 5 marks

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  [5.1] The marks for this question were lower than expected. Students did not know that an acid chloride will produce misty fumes of HCl and give an immediate white precipitate of AgCl on addition of silver nitrate solution. More knew that there would be no immediate visible reaction with the 1-chloropropane, followed by the slow formation of a white precipitate. Either of these would have gained the second mark.

  Text version

  This question is about simple test-tube reactions used to identify organic liquids.

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• AQA 7405 · June 2024 · Paper 2 · Q6 · 12 marks

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  [6.1] This equation was quite well answered but also differentiated well.

  Text version

  Compounds V, W, X and Y are isomers with molecular formula C5H10O2. V and W are carboxylic acids whose formulae can be written C4H9COOH.

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• AQA 7405 · June 2024 · Paper 2 · Q9 · 9 marks

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  [9.2] Over half the students got at least 1 mark and the skeletal structures seen were much better attempted than in some past papers.

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  This question is about amines.

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• AQA 7405 · June 2024 · Paper 2 · Q10 · 12 marks

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  [10.1] This extended response question on the structure and bonding in benzene had a mean mark of almost 3 out of 5. Virtually all of the students were able to score some of the marks, and almost 40% gained at least 4 marks.

  Text version

  Figure 5 gives enthalpies of hydrogenation to cyclohexane: cyclohexene, -120 kJ mol^-1; theoretical cyclohexa-1,3,5-triene, -360 kJ mol^-1; benzene, -208 kJ mol^-1. A later synthesis starts with 1,2-dimethylbenzene, nitrates it at the position para to the methyl group at carbon 1, then reduces the nitro group to form the corresponding aromatic amine.

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• AQA 7405 · June 2024 · Paper 3 · Q3 · 10 marks

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  Nearly 90% of students gained the mark for 03.1. 03.2 was another example of a slightly unusual context for this question and students needed to recognise that the units of k (s–1) were the key to identifying that the reaction is first order. 03.3 was another graph question; the scales being provided made it more accessible though there was still some misreading of the scales. In 03.4 students needed to recognise that the Arrhenius equation given in the question is of the form y = mx + c, so a plot of ln k vs 1/T will give a straight line of gradient -Ea/R. Calculating the gradient therefore leads to a value for Ea. Some students tried to substitute values into the whole equation but failed to realise that the y-axis intercept was not at 0 on the x-axis so the value of lnk at that intercept would not be equal to ln A. 03.5 tested the ability to apply information from the start of the question where the equation for the thermal decomposition of but-3-en-1-ol was given and to apply it to a different compound. Many students failed to respond to the need for a carbonyl as one of the products and suggested alcohols or acids instead.

  Text version

  But-3-en-1-ol decomposes thermally by CH2=CHCH2CH2OH -> CH2=CHCH3 + HCHO. Rate constants are measured at different temperatures. The table columns are T / K, 1/T / K^-1, k / s^-1 and ln k. Rows are: 553, 1.81 x 10^-3, 4.6 x 10^-4, -7.68; 563, 1.78 x 10^-3, 8.4 x 10^-4, -7.08; 573, two missing entries, 15.6 x 10^-4; 583, 1.72 x 10^-3, 28.0 x 10^-4, -5.88; 593, 1.69 x 10^-3, 49.9 x 10^-4, -5.30.

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• AQA 7405 · June 2023 · Paper 2 · Q1 · 7 marks

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  [01.1] This unfamiliar practical question proved difficult and relatively few students scored the mark for an appreciation that the narrow neck of a conical flask will reduce the loss of droplets of liquid in a reaction giving effervescence.

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  An acid reacts with excess solid sodium hydrogencarbonate, NaHCO3, in a vessel placed on a balance. The timer starts when NaHCO3 is added, and the mass of CO2 lost is recorded. A conical flask with a narrow neck is shown, open so that gas can escape. With 25.0 cm^3 of 2.23 mol dm^-3 ethanoic acid, the graph of mass of CO2 lost against time starts at (0 min, 0 g), passes approximately through (0.5, 0.7), (1.0, 1.3), (1.5, 1.8), (2.0, 2.1), (2.5, 2.3) and reaches a plateau of about 2.4 g at 3.0 min, remaining level thereafter.

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• AQA 7405 · June 2023 · Paper 2 · Q3 · 12 marks

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  [03.1] As with the other two parts of this question, the discrimination index of more than 0.65 showed that this type of question discriminates very well. Able students often scored all four marks for this familiar mechanism despite the unusual way the question demanded that students work backwards from the given intermediate for the first three marks.

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  This question concerns intermediates in three organic reaction mechanisms.

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• AQA 7405 · June 2023 · Paper 2 · Q4 · 15 marks

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  [04.4] The reagent and condition mark was scored by large numbers of students but the equation proved far more difficult and only just over a quarter scored full marks here. The question had a high discrimination index and identified the best students.

  Text version

  Acrylonitrile, H2C=CHCN, is converted by HBr in reaction 1 into isomer W, BrCH2CH2CN. Reaction 2 converts W into NCCH2CH2CN, which reaction 3 converts into H2N(CH2)4NH2. Butane-1,4-diamine can form nylon 4,6 with hexanedioic acid.

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• AQA 7405 · June 2023 · Paper 2 · Q5 · 11 marks

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  [05.6] This question was well answered and there were several alternative ways students could approach the question. Most focused on the lack of integration data on the spectrum but fewer gave the anticipated response about the peaks at δ=2.60 and 2.58 overlapping and making the splitting patterns difficult to interpret.

  Text version

  Compound Z has molecular formula C7H12O3. Its IR spectrum has a strong absorption at 1725 cm^-1. Its 13C NMR spectrum has seven peaks, including one at delta = 174 ppm. Its 1H NMR data are: delta 4.10, integration 2, quartet; 2.60, integration 2, triplet; 2.56, integration 2, triplet; 2.19, integration 3, singlet; 1.26, integration 3, triplet. The plotted 1H spectrum itself shows no integration values and has adjacent signals around 2.6 ppm.

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• AQA 7405 · June 2023 · Paper 2 · Q6 · 14 marks

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  [06.3] This question on familiar organic tests was answered quite well with around 80% able to score at least half marks. The observations for M2, M4, M6 and M8 were very well known, but the substances that would react in each test were less well understood. The question had a high discrimination index.

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  Four liquids are: J = CH3CH2CH(OH)CH2COOH; K = CH2=C(CH3)COCH3; L = HOOCCH2C(OH)(CH3)2; M = CH3CH2CH2CHO. A student proposes four tests on separate samples: test 1, add potassium dichromate(VI) solution and warm gently; test 2, add Fehling's solution and cool in iced water; test 3, add sodium hydrogencarbonate solution and test any gas with a lighted splint; test 4, add bromine water and shake at room temperature.

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• AQA 7405 · June 2023 · Paper 2 · Q8 · 19 marks

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  [08.6] The most common issue with the answers to this question was the failure to show sufficient workings. Better students showed values for the sums of the bond enthalpies for bonds broken and bonds formed. Even if a mistake was made in these values the final mark could be scored consequentially for their correct use in calculating the approximate value for the enthalpy change. Over 70% were able to score at least one of the three marks available.

  Text version

  This question concerns biofuels. Palmitic acid is CH3(CH2)14COOH. Palm oil contains the triester formed when all three OH groups of glycerol react with palmitic acid. Ethanol can be made by fermentation: C6H12O6 -> 2C2H5OH + 2CO2.

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• AQA 7405 · June 2023 · Paper 2 · Q9 · 12 marks

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  [09.3] This question required students to demonstrate their understanding that the Arrhenius equation could be rearranged to find the temperature for this reaction. Over half were able to score at least two of the three marks. The most common mistake was a failure to convert the activation energy given into a value in J mol–1.

  Text version

  In the gas phase, ethanoic anhydride decomposes: (CH3CO)2O -> H2C=C=O + CH3COOH. Ethenone is the simplest ketene; ketenes contain one C=C and one C=O bond.

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• AQA 7405 · June 2023 · Paper 3 · Q2 · 8 marks

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  Most of question 2 required students to be familiar with the dehydration of alcohols to form alkenes and therefore with the idea that the reaction involves the loss of OH from one C atom and the loss of an H from an adjacent C atom. Familiarity with the concept of isomerism was also required. In 02.1, a displayed formula for pentan-1-ol was required (but only 36% of students correctly gave this answer) and the commonest reasons for the mark not being awarded were that the OH group was not displayed or that pentan-3-ol was suggested. 02.2 was answered better and it was pleasing to see an increased facility with which students were able to represent structures using skeletal formulae – but note that, in this case, the OH group must NOT be displayed. Despite students not being very familiar with ethers, a majority of students were able to score in question 02.3. 02.4 proved one of the trickier questions on the paper with only 16% of students scoring here. The commonest error was to offer a tertiary alcohol as the answer – this suggested confusion about which alcohols cannot be oxidised rather than which cannot be dehydrated. 50% of students scored 3 marks in 02.5 and students are again reminded of the importance of being precise when drawing curly arrows in terms of where they start and where they finish. A curly arrow in any mechanism must always start either from the line representing a covalent bond or from a lone pair drawn on an atom. In this case, both arrows should have started from an existing bond in order to represent the breaking of that bond. 02.6 was a test of the understanding that dehydration involves the loss of the OH along with a H atom from an adjacent carbon. Only 30% of students could give the correct structure.

  Text version

  This question concerns isomerism and dehydration of alcohols. Pentan-2-ol has molecular formula C5H12O.

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• AQA 7405 · June 2023 · Paper 3 · Q3 · 12 marks

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  Many students only scored 1 mark for 03.1, either due to just drawing NH2 as an addition to the partial structure given or to drawing Phe correctly but with a COOH terminal group instead of the CONH2 described in the question. 03.2 required students to deduce the structure of proline by working out what would remain from hydrolysing the peptide groups either side of proline in the partial structure given. 27% of students were able to do this. The commonest error was, as expected, to show an NH2 group instead of NH. In 03.3, the need for reflux with 6 mol dm–3 HCl is not well known by students – but nor is it specified in the specification. Therefore a wide variety of more generic answers related to the hydrolysis of amide links was also allowed, such that 80% of students were able to score 1 or 2 marks. In 03.4, the key idea of this sort of chromatography (which is the need for the atmosphere in the tank to be saturated with vapour of the mobile phase) is clearly not well known by students, although it was pleasing to see a few such references. Again, various other valid suggestions were allowed as alternatives. Many students got confused between TLC and paper chromatography and were therefore led into talking about the need to support the paper so that it stood up in the beaker. 03.5 was a direct test of a statement in the specification, which refers to there being a balance between solubility in the mobile phase and retention on the stationary phase. Many answers were incorrect because they only referred to solubility in the mobile phase. 03.6 was quite well answered although some students suggested the use of UV – but this is not appropriate as something that is sprayed onto the TLC plate as described in the question. 78% of students were able to correctly calculate the Rf value in 03.7.

  Text version

  Endomorphin-2 is a peptide with the amino-acid sequence Tyr-Pro-Phe-Phe-NH2. A partial displayed structure ending after Tyr-Pro-Phe is provided. The question also concerns peptide hydrolysis and thin-layer chromatography (TLC) of amino acids.

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• AQA 7405 · June 2022 · Paper 2 · Q1 · 21 marks

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  [01.8] This question had a very high discrimination index and the best students were able to score full marks. Common errors included poor drawing of curly arrows and mistakes in the structure of the intermediate.

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  Acidified butanone reacts with iodine: CH3CH2COCH3 + I2 -> CH3CH2COCH2I + HI.

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• AQA 7405 · June 2022 · Paper 2 · Q2 · 11 marks

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  [02.2] This was a very straightforward equilibrium constant expression that the vast majority of students were able to answer correctly.

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  Tetrafluoroethene is made by 2CHClF2(g) <=> C2F4(g) + 2HCl(g), delta H = +128 kJ mol^-1. Initially 2.00 mol CHClF2 is placed in 23.2 dm3; at equilibrium 0.270 mol remains.

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• AQA 7405 · June 2022 · Paper 2 · Q3 · 11 marks

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  [03.1] The second mechanism on the paper also had a high discrimination index and the best students were able to score full marks here. Most students were able to get started but mistakes in the structure of the tertiary carbocation intermediate were quite common, as were errors in representation of the sulfuric acid, and subsequent attack on the carbocation by the hydrogensulfate ion.

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  This question is about 2-methylbut-1-ene, CH2=C(CH3)CH2CH3.

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• AQA 7405 · June 2022 · Paper 2 · Q4 · 9 marks

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  [04.1] Very well answered with the vast majority able to identify this type of structure as primary.

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  Proteins are polymers of amino acids. A section has the sequence -Cys-Ser-Asp-Phe-.

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• AQA 7405 · June 2022 · Paper 2 · Q5 · 12 marks

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  [05.2] Removal of water-soluble impurities as the correct reason for adding distilled water was less well known.

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  Hexan-2-ol is immiscible with water and boils at 140 degrees C. It is prepared by adding concentrated phosphoric acid to 11.0 cm3 hex-1-ene in an ice bath, adding water, separating and washing the organic layer with water, drying with anhydrous MgSO4, filtering under reduced pressure, then distilling and collecting 130-160 degrees C.

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• AQA 7405 · June 2022 · Paper 2 · Q7 · 6 marks

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  [07.3] The specific role of the methoxide ion as a base/ proton acceptor was better answered than Question 07.2.

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  Aqueous NaOH hydrolyses methyl ethanoate. Hydroxide attacks CH3C(=O)OCH3 to form tetrahedral CH3C(OH)(O-)(OCH3), which collapses to CH3COOH and CH3O-. Methoxide then gives CH3COO- and CH3OH.

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• AQA 7405 · June 2022 · Paper 2 · Q8 · 7 marks

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  [08.3] A good proportion of students scored all 3 marks for this familiar mechanism and most were able to score some marks here.

  Text version

  Benzene reacts with methanoyl chloride, HCOCl, in a Friedel-Crafts acylation.

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• AQA 7405 · June 2022 · Paper 2 · Q9 · 12 marks

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  [09.5] The question demanded that students show their working. Whilst it was well answered overall, many failed to score both marks. The first mark required students to show that the Mr was one less than 345, but this was often omitted despite the question stating that each molecule gains a hydrogen ion (H+) during electrospray ionisation.

  Text version

  Olive oil is 85% by mass of unsaturated triester Y, C57H100O6, Mr 880, plus inert impurity. Each Y molecule contains five C=C bonds. A weighed oil sample is made to 250 cm3 with inert solvent, and 25.0 cm3 portions are titrated with 0.025 mol dm^-3 Br2(aq).

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• AQA 7405 · June 2022 · Paper 2 · Q10 · 10 marks

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  [10.1] Few students scored all three marks despite the reactions being very common in previous papers.

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  A synthesis starts from methylbenzene. Step 1 forms para-nitromethylbenzene; step 2 reduces NO2 to para-CH3C6H4NH2, amine A; step 3 converts A to para-CH3C6H4NHCOCH3. In another branch, step 4 converts methylbenzene to C6H5CH2Cl; step 5 converts this to C6H5CH2NH2, amine B.

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• AQA 7405 · June 2022 · Paper 3 · Q3 · 15 marks

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  03.1 was recalled by most students although ‘nucleophilic elimination’ was incorrectly suggested by some for the mechanism to form the alkenes. Clarity of description was again somewhat lacking in 03.2 – which is a definition best learnt by rote as “molecules with the same structural formula but a different spatial arrangement of atoms”. ‘Molecular’ was often substituted for ‘structural’ and the phrase ‘different spatial arrangement’ often lacked a reference to atoms (or bonds or groups). In 03.3 most students were able to correctly name but-1-ene but explanations for its lack of stereoisomerism were often unclear. It is not enough to refer to ‘two Hs on the same side of the C=C’ as the word ‘side’ is ambiguous here. The best way to be clear is to refer to the fact that one of the C atoms involved in the double bond has two atoms the same bonded to it. In 03.4 ‘error carried forward’ was applied for any student who had mistakenly identified the product as but-2-ene in 03.3, so full marks were still available to those students for the mechanism. It is recommended that students should draw clearly displayed structures and draw them a bit larger than if just showing the structure – this allows more space so that the positioning of curly arrows is clear. 03.5 was well answered. 03.6 showed that more practice is needed by some students at drawing 3D representations in a conventional manner. The recommended style is: There was a wide variety of misconceptions evident in the answers to 03.7 with various references to halide ions in the halogenoalkane molecules, to sizes of ions or atoms and to electronegativity. As stated in the specification, all that is needed to explain the relative rates of hydrolysis is to refer to the relative bond strengths of C–I, C–Br and C–Cl.

  Text version

  Under suitable conditions, 2-bromobutane reacts with sodium hydroxide to form five products. A, B and C are alkenes: A is a structural isomer of B and C and has no stereoisomerism, while B and C are stereoisomers. D and E are alcohol enantiomers.

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• AQA 7405 · June 2022 · Paper 3 · Q5 · 11 marks

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  05.1 was well answered by most students. In 05.2 many students either did not notice that there were six marks available or were not able to work out how to access them as many answers were very brief and generic. The question specifically asked for suitable equations to be included but these were often left out of answers. 05.3 saw the greatest evidence of confusion in the use of correct terminology. One of the key aspects of the topic on electrochemistry and electrode potentials is its reliance on conventional terms of reference. When referring to an electrode potential it is advised that students stick to the conventional form. e.g. Eo S2O82–/SO42– is greater than Eo Co3+/Co2+ Therefore any references to electrode potentials and half-cell equations should follow the convention of showing (or implying) a reduction in the forward direction. A commonly seen example of a lack of clarity was “The electrode potential for Co2+ is less than that for S2O82– but more than for iodide so it can oxidise one and reduce the other.” Apart from the reference to “The electrode potential for Co2+” being incorrect it is not clear from this what is oxidising or reducing what. This is a particular example of a situation where references to ‘it’ are likely to be ambiguous. Many answers were also difficult to mark because of carelessness with CO instead of Co and confusion between subscripts and superscripts e.g. CO3+ Section B – Multiple Choice Some students need to pay more careful attention to the instructions given at the start of Section B about how to complete the answers by shading in the lozenge, crossing out an incorrect answer and then circling a crossed-out answer if it is then decided to be correct. There were quite a few instances of crossed-out and circled answers alongside shaded lozenges – which has to be treated as two answers and so marked incorrect. Questions students found particularly straightforward, with correct answers from at least 80% of the cohort, were B32, B34, B18, B25, B23. Questions that proved to be particularly challenging were B10, B33, B28, B7.

  Text version

  This question concerns heterogeneous, auto- and homogeneous catalysis. Table 6 gives standard reduction potentials: S2O8^2- + 2e- -> 2SO4^2-, +2.01 V; Co3+ + e- -> Co2+, +1.82 V; I2 + 2e- -> 2I-, +0.54 V.

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• AQA 7405 · November 2021 · Paper 2 · Q1 · 15 marks

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  All aspects of this question differentiated very well. The extended calculation in question 01.3 attracted good responses with a third of the students gaining full marks and the majority able to access at least 1 or 2 marks. A common mistake was to assume that the oil was pure triester. In question 01.4 very few students appreciated that aqueous ethanol was used as a mutual solvent for both the oil and the potassium hydroxide.

  Text version

  Coconut oil contains a triester with three identical R groups. This triester reacts with potassium hydroxide.

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• AQA 7405 · November 2021 · Paper 2 · Q2 · 19 marks

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  In this question a surprisingly small proportion of students were able to state the meaning of the term fraction. In addition, very few were able to explain why C=O bonds in carbon dioxide absorb infrared radiation. A good range of answers was seen for the extended response question about the environmental impact of bioethanol as a fuel, but a significant number of students were unable to get started here.

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  This question covers petrol fractions, cracking, infrared absorption by carbon dioxide, removal of CO2 with 2-aminoethanol and the environmental case for bioethanol.

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• AQA 7405 · November 2021 · Paper 2 · Q4 · 9 marks

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  Question 04.1 gave a good range of scores and a third of students were able to score at least 2 marks. The common errors included multiplying the value of enthalpy of atomisation for hydrogen by 3 rather than 6. Question 04.3 required students to apply mechanistic ideas to structures that were provided. The vast majority of students were able to score some marks on this question and it also proved to be a very good discriminator.

  Text version

  Figure 3 compares delocalised benzene(g) with hypothetical Kekule cyclohexa-1,3,5-triene(g). Benzene formation from 6C(s) + 3H2(g) has Delta H1 = +83 kJ mol^-1. Table 1: atomisation C +715, atomisation H +218, C-C +348, C=C +612, C-H +412 kJ mol^-1.

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• AQA 7405 · November 2021 · Paper 2 · Q5 · 7 marks

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  The algebraic approach needed in question 05.1 proved difficult for some but around half the students were able to score full marks here. The structure of the diester in question 05.2 was very poorly answered, but the familiar Kc calculation in question 05.3 proved very accessible and around two thirds of students scored all three marks.

  Text version

  Diester hydrolysis: C7H12O4 + 2H2O <=> 2CH3COOH + HO(CH2)3OH.

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• AQA 7405 · November 2021 · Paper 2 · Q6 · 7 marks

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  Answers to question 06.3 about the E and Z forms of a structure that shows both geometric and optical isomerism were very poor and over 70% of students failed to score either mark. Questions 06.2 and 06.4 proved more accessible.

  Text version

  This question concerns C5H10O isomers showing optical, geometric and cyclic ether isomerism.

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• AQA 7405 · November 2021 · Paper 2 · Q7 · 9 marks

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  Over 75% of students scored the mark for question 07.1 and there was a good range of marks seen for question 07.2, with many able to score at least 1 mark here. Less than 20% of students scored 3 or more marks for question 07.3. The lack of a suitable explanation for splitting patterns and chemical shifts was the most common problem. That said, a significant number were able to score the mark for deducing the structure.

  Text version

  Spectroscopy of K (C4H8O), hydrogenation of nitrile L (C4H7NO), and proton NMR of Q (C3H7ClO). For Q, peaks are 3.95 ppm (0.6), 3.65 ppm (0.6), 3.35 ppm (0.9).

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• AQA 7405 · November 2021 · Paper 2 · Q8 · 13 marks

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  Few students scored 3 or more marks on question 08.2. Both the reagents and equations proved very challenging, with over 50% either failing to score or not attempting this question. A very good range of marks was seen for question 08.3 and the question discriminated very well.

  Text version

  Synthesis scheme: cyclohexanol -> cyclohexene -> compound G -> cyclohexane-1,2-diol -> cyclic diester with ethanedioyl dichloride.

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• AQA 7405 · November 2021 · Paper 2 · Q9 · 7 marks

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  Students scored poorly on question 09.2 and few appreciated that the breakage of the C-Cl bond was the key point. A high proportion of students scored well on question 09.3 about catalytic ozone decomposition. Many also scored good marks on question 09.4 by being able to derive equations for novel propagation steps.

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  This question concerns ozone protection, CFC photodissociation, catalytic ozone destruction and free-radical chlorination forming an HCFC.

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• AQA 7405 · November 2021 · Paper 3 · Q6 · 13 marks

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  Practical weaknesses and insufficient precision in answers let many students down here. Question 06.1 specifically asked for safety concerns related to the apparatus diagram, with the hope that students would recognise that the bung should not be present (as it would mean a sealed apparatus is being heated) and that the flask is not clamped. Vague references to ‘the clamp being in the wrong place’ were not sufficient because a more specific response was needed. Many students referred to the direction of the water flow being wrong because it should enter at the bottom of the condenser – but this is not a safety concern so could not be credited here. However, if it was mentioned in 06.1 but not then mentioned in 06.3, credit was still allowed for 06.3. In question 06.3 many students failed to recognise that the thermometer is not needed at all and got confused with distillation by suggesting that the thermometer needed to be higher up in the apparatus. Section B The mean score on Section B was 17.7 out of 30 (59%). The five most straightforward questions (answered correctly by more than 80% of students) proved to be B7, B10, B22, B23 and B28. The five most challenging questions (answered correctly by fewer than 40% of students) were B12, B15, B25, B26 and B31. Multiple-choice items that discriminated particularly well (i.e. there was a good correlation between performance on the item and overall performance on the paper) across the range of ability of the students were B8, B21, B29, B30, B33 and B34. Multiple-choice items that did not discriminate very well at all were B12 and B15.

  Text version

  A student plans to oxidise propan-1-ol to propanoic acid. Figure 4 shows a heated round-bottomed flask containing propan-1-ol, potassium dichromate(VI) and small glass beads, below a vertical condenser. Only the condenser is clamped; a bung seals its top around a thermometer extending into the flask; cooling water enters at the top and leaves at the bottom.

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• AQA 7405 · November 2020 · Paper 2 · Q3 · 13 marks

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  A common problem in this question was being unable to identify common features that linked some of the isomers. As such, many included isomers that did not fit the demand in each of the first three parts of the question. The expected observations for test tube reactions in 03.1 and 03.2 were well known. 03.3 proved more difficult with students finding it hard to identify neutralisation of excess acid as the reason why the esterification reaction mixture was poured into NaHCO3 solution. 03.4 was very well known. Large numbers of students could identify infrared absorptions that could be used to distinguish isomers in 03.5, but far fewer appreciated that the fingerprint region should be used to distinguish those that had common absorptions above 1500 cm–1.

  Text version

  Six C6H12O structural isomers are labelled P-U: P is a tertiary cyclopentanol, Q is a primary alcohol, R and S are secondary cyclopentanols, T is hexanal and U is hexan-3-one.

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• AQA 7405 · November 2020 · Paper 2 · Q4 · 16 marks

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  This question covered the skills learned in completing required practical 10 but a surprising number of students were unable to suggest re-weighing the weighing boat as the missing step in the method for 04.1. Few students appreciated the need to state an appropriate size for the apparatus to be used to measure out the ethanoic anhydride in 04.2. The calculation in 04.5 was very well answered. Students were often able to identify that impurities lower the melting point of a sample in 04.6 but far fewer appreciated that impurities also broaden the range of temperatures over which the impure sample melts. In 04.7, many students were able to suggest keeping the mixture away from naked flames but far fewer identified that keeping the mixture below the boiling point of ethanol would also be an appropriate precaution to take. 04.8 proved difficult and only the best students explained that washing the aspirin with cold ethanol would be done to remove soluble impurities. 04.9 was well answered.

  Text version

  Aspirin is prepared by reacting salicylic acid with ethanoic anhydride, using concentrated phosphoric acid, cooling, filtering and recrystallising from ethanol.

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• AQA 7405 · November 2020 · Paper 2 · Q6 · 10 marks

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  06.1 was reasonably well answered but few students were able to identify suitable conditions for this acylation reaction. 06.2 also proved to be quite a low scoring question despite the familiarity of this reaction in many previous exams. The dehydration mechanism in 06.3 was poorly answered compared to other mechanism questions in the paper.

  Text version

  Polystyrene is made from benzene via acetophenone, 1-phenylethanol and phenylethene.

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• AQA 7405 · November 2020 · Paper 2 · Q7 · 12 marks

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  07.1 was marked with a levels of response mark scheme and required students to communicate their answers coherently with logical progression. The role of Si(CH3)4 in NMR was quite well understood but few students knew that CDCl3 and CCl4 are used as solvents. This lack of knowledge meant the highest level was hard to access. Only the very best students were able to explain the link between solvent chosen and the polarity of the sample. Around 43% of students scored at least 3 marks here but less than 10% scored 5 or 6 marks. Students were good at identifying at least some of the splitting patterns required in 07.2, but 07.3 proved very challenging. 07.4 required students to deduce structures for isomers based on the number of singlet peaks and integration ratios in the 1H NMR spectra, but responses often failed to fit with these requirements.

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  This question is about proton NMR spectroscopy and CH3CHClCOCH(CH3)2.

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• AQA 7405 · November 2020 · Paper 2 · Q8 · 9 marks

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  Fewer than 10% of students scored 4 or 5 marks for the calculation in 08.1, but the first three marks proved much more accessible. Students were often unable to link the amount in moles of CO2 produced in combustion to the amount of carbon in the original sample. Even fewer were able to do this to determine the amount in moles of hydrogen from the amount of water produced. 08.2 proved more accessible and many students scored both marks, with a variety of methods used. 08.3 was well answered but 08.4 was only scored by around 40% of students.

  Text version

  Citric acid hydrate is H3Y.xH2O; anhydrous citric acid has displayed structure HOOC-CH2-C(OH)(COOH)-CH2-COOH.

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• AQA 7405 · November 2020 · Paper 2 · Q9 · 18 marks

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  The first two parts of the question were very well answered and students often scored high marks. 09.3 was much less well answered, with fewer than 20% of students able to suggest that the concentration of water being effectively constant is the reason why the equilibrium expression can be written without including it. 09.4 was another calculation where many students got started but few were able to access the highest marks. Only the very best identified that an algebraic approach was needed to calculate the required equilibrium concentration. 09.5 required students to apply their understanding of standard mechanistic ideas to a novel mechanism. Most students were able to score at least some of the marks and a good number (44.3%) scored all three marks. Full marks proved far more difficult in 09.6 but students often gained some credit for recognising that the alkyl group would be electron donating. Concluding Remarks Overall the questions in this paper proved to be of a similar standard to those in previous series. The paper differentiated well, and students were able to complete the questions in the time available. All questions were correctly answered by a good number of students apart from 07.3 which was the most difficult question on the paper.

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  A(aq) + 2B(aq) <=> C(aq), followed by equilibria for hydration of chloroethanal.

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• AQA 7405 · November 2020 · Paper 3 · Q4 · 15 marks

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  In 04.1, as is often the case when a piece of syllabus recall is tested for the first time, relatively few students were able to recall the name of the process prevented by cisplatin during cell division. Students were expected to answer 04.2 by following the description in the question of a chloride ligand being replaced by a water molecule. In many cases students failed to appreciate that replacement of a negative chloride ion by a neutral water molecule would result in a net charge (of 1+) on the resulting complex. 04.3 proved to be very tricky for many students – perhaps due to the amount of reading needed to pick up on the clues in the question and to appreciate what was being asked. Students are clearly more familiar with questions asking them to show hydrogen bonding between base pairs because that is what many tried to do – and they ignored the need to include the complex in their diagram. Where the complex was included it was sometimes drawn as trans- rather than cis- and often without an indication that the bonds formed are co-ordinate bonds. The experiment in 04.4 was another example of a situation where a description of a (hopefully familiar) practical scenario was needed. Students found this very taxing and over half scored no marks. The question described measurements of concentration being taken at one-minute intervals and then asked for a description of graphical methods. Although there were several alternative possibilities, they all needed to start with a description of the need to plot a graph of these measured concentrations against time. The next stage needed to be some reference to a determination of rate from the concentration-time graph. When referring to a subsequent rate- concentration graph it is not enough to refer to a ‘straight line of constant gradient’ as that could also be a zero order line – a sketch graph was useful to some students here. The idea of constant half-lives is not on the syllabus, so this type of answer was not expected but was credited if seen. Most were able to complete the two simple calculator processes in 04.5 although some students seemed to try and arrive at the answers by using the successive differences between previous values in the table. However they failed to spot that the temperature differences were not all the same. Answers to 04.6 showed an improvement in graph skills with 70% of students scoring at least 3 marks. The negative scale confused some students and some forgot the need for at least 50% of the available space to be taken up by the plotted points. Most students then recognised that the gradient = Ea/R but some tried to solve the whole equation by inventing values for the ln terms. In some cases gradient calculations were the wrong way up or involved a misreading of the scales, e.g. 0.00341 was often seen as the value for ∆x instead of (0.00341 – 0.00310).

  Text version

  Cisplatin, cis-[Pt(NH3)2Cl2], is an anticancer drug. In aqueous solution it forms a species that bonds to adjacent guanine bases in DNA. Kinetic data for this process are analysed using concentration-time and Arrhenius plots.

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• AQA 7405 · June 2019 · Paper 2 · Q1 · 12 marks

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  [01.2] The mechanism was answered well although some students drew an intermediate with too few carbons. The structure of a cyclic secondary amine proved difficult for some to deduce and many incorrect hexagons or primary amine structures were drawn.

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  Amines: preparation, nucleophilic substitution, basicity and chirality.

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• AQA 7405 · June 2019 · Paper 2 · Q2 · 12 marks

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  [02.1] Most of this question was based on Required Practical Activity 5 example (a), from the Practical Handbook. Sadly, this experimental procedure did not seem familiar to many students and few completed the diagram correctly.

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  Preparation and purification of cyclohexene from cyclohexanol.

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• AQA 7405 · June 2019 · Paper 2 · Q3 · 9 marks

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  [03.2] Over half the students drew a correct structure but only a very small number could give its correct IUPAC name as buta-1,3-diene.

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  Polyisoprene and stereoisomeric addition polymers used in golf balls.

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• AQA 7405 · June 2019 · Paper 2 · Q11 · 11 marks

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  [11.2] Part 2 was challenging and almost a quarter of students made no attempt to answer the question. The left hand (glycerol) part of the molecule was better known. Some students miscounted the carbon atoms in the acid part by including the methyl group of the biodiesel in the oil. Another common mistake was to draw the COO linkage the wrong way round.

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  Esters, vegetable-oil biodiesel, stereochemistry, combustion and greenhouse warming.

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• AQA 7405 · June 2019 · Paper 2 · Q12 · 5 marks

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  [12.1] The way that the DNA strands had been presented helped many students to score both marks in the first part of the question. Those who did make mistakes usually added extra hydrogen bonds, thereby failing to gain at least one of the marks they might otherwise have gained.

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  Hydrogen bonding, nucleotide components and complementarity in a DNA double helix.

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• AQA 7405 · June 2019 · Paper 2 · Q13 · 7 marks

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  [13.2] Nearly two-thirds of students scored both marks in this question. A common incorrect answer was to suggest acidified potassium dichromate as the reagent when it would not, of course, distinguish between the aldehyde and the alcohol formed.

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  Selective sodium borohydride reduction and tests for incomplete aldehyde reduction.

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• AQA 7405 · June 2019 · Paper 3 · Q4 · 9 marks

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  [4.2] A key phrase in this question was “explain how the structure of ethanal leads to the formation of two isomers”. This wording was unfortunately missed by many students who instead referred to the structure of the product and wrote about the chiral carbon. Those who recognised the need to refer to the planar carbonyl group sometimes made the mistake of referring to ethanal itself as planar – which is not true for the whole molecule. There are many different ways of drawing 3D representations, but the style shown in the mark scheme is recommended for clarity. Enantiomers should either be shown by drawing the second image as a mirror of the first, or by drawing the same orientation as the first but with two groups swapped round.

  Text version

  Ethanal reacts with potassium cyanide followed by dilute acid to form 2-hydroxypropanenitrile, CH3CH(OH)CN. This product can be converted to acrylonitrile and polymerised.

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• AQA 7405 · June 2018 · Paper 2 · Q1 · 10 marks

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  [01.1] The equation was an easy starter and 90.1% of the students gained the mark.

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  Combustion, cracking, radical substitution and ozone depletion by CFCs.

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• AQA 7405 · June 2018 · Paper 2 · Q6 · 9 marks

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  Cyclohexene and Benzene

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  Bonding, stability and hydrogenation enthalpies of benzene and conjugated dienes.

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• AQA 7405 · June 2018 · Paper 2 · Q7 · 10 marks

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  [07.2] In this question, although some students struggled with the name, a number failed to gain the mark due to a failure to label 1-phenyl in an otherwise correct name. Most identified a correct reagent but “electrophilic addition” and “reduction” were frequent wrong answers for the name of the mechanism.

  Text version

  Friedel-Crafts acylation and reactions of 1-phenylpropan-1-ol.

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• AQA 7405 · June 2018 · Paper 2 · Q11 · 6 marks

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  [11.2] This was the most familiar of the three isomers required and was correctly answered by 55.3% of students. The most common errors seen were cyclic or aromatic structures or those with an incorrect number of carbon atoms in the chain. A disappointing proportion of students (17.5%) made no attempt to answer the question.

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  NMR and symmetrical isomers of C6H16N2.

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• AQA 7405 · June 2017 · Paper 2 · Q1 · 13 marks

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  [01.5] Both the reagent (which must be a complete compound) and a condition were needed to score the mark; several omitted the condition.

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  Reactions of 1-bromopropane.

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• AQA 7405 · June 2017 · Paper 2 · Q4 · 8 marks

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  [04.3] The first mark was less commonly scored than expected as many students wrote about a planar molecule or a planar bond rather than planar carbonyl group; the other two marks were frequently awarded.

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  Cyanohydrins and optical isomerism.

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• AQA 7405 · June 2017 · Paper 2 · Q7 · 6 marks

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  [07.1] There were some very good answers to this question and nearly a fifth of the students scored full marks. The best answers followed a ‘stage approach’, in which a first test divided the four compounds into two groups. Subsequent tests were then made on each group. Students generally knew the chemistry, but didn’t always show a logical approach in their answers to the problem. Some suggested testing the same reagents on all four compounds, failing to appreciate that once one compound was identified, further tests on it were unnecessary. Some suggested performing isolated tests on individual compounds.

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  Minimum-test identification of four multifunctional compounds.

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• AQA 7405 · June 2017 · Paper 2 · Q8 · 12 marks

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  [08.3] Only the very weakest 7% of students failed to calculate the correct Rf value.

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  Nitration of nitrobenzene and TLC of dinitrobenzene isomers.

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• AQA 7405 · June 2017 · Paper 2 · Q9 · 4 marks

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  [09.1] This question tested a topic new to the specification and it was pleasing that just over half of the students were able to answer this part correctly.

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  DNA nucleotide groups and adenine-thymine hydrogen bonding.

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• AQA 7405 · June 2017 · Paper 2 · Q11 · 11 marks

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  [11.1] The full range of marks was seen and included some excellent answers. Other responses did not contain accurate descriptions of the effect of the attached groups on the availability of the lone pair on the nitrogen atom. The idea that, for nitrogen atoms directly attached to the benzene ring, the lone pair was delocalised into the ring was often poorly explained. The (positive) inductive effect of alkyl groups was much better described.

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  Basicity and synthesis of aromatic amines E, F and G.

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• AQA 7405 · sample1 · Paper 3 · Q5 · 6 marks

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  Mass spectra of ethanedioic-acid esters.

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