AQA A-Level Chemistry 2027 Predicted Practice Paper — Paper 1

Answer ALL questions. Write your answers in the spaces provided. You must write down all the stages in your working.

Section A

Short-answer and structured questions. Answer ALL questions.

• 1

  Question SECTION-A1 (7 marks)

  Vanadium exhibits several oxidation states in aqueous solution. (a) State the electronic configuration of a vanadium atom (Z = 23) using s, p and d notation. (1 mark) (b) An acidified solution of ammonium vanadate(V) containing the VO2^+ ion is added to an excess of zinc in dilute sulfuric acid. The solution changes colour through a series of oxidation states. Give the oxidation state of vanadium in VO2^+, and identify the FINAL vanadium species (formula) and its oxidation state once reduction by excess zinc is complete. (3 marks) (c) Explain, in terms of electrons, why zinc is able to reduce VO2^+ but a solution containing only Fe^2+ ions cannot reduce VO2^+ all the way to the +2 state. Use the following standard electrode potentials in your answer: E(Zn^2+/Zn) = -0.76 V; E(Fe^3+/Fe^2+) = +0.77 V; E(V^3+/V^2+) = -0.26 V. (3 marks)

  (Total for Question SECTION-A1 is 7 marks)
• 2

  Question SECTION-A2 (7 marks)

  Propanoic acid, CH3CH2COOH, is a weak monoprotic acid with Ka = 1.34 x 10^-5 mol dm^-3 at 298 K. (a) Write an expression for Ka for propanoic acid. (1 mark) (b) Calculate the pH of a 0.150 mol dm^-3 solution of propanoic acid at 298 K. Give your answer to 2 decimal places. (3 marks) (c) A buffer solution is made by adding 0.0500 mol of solid sodium propanoate to 1.00 dm^3 of the 0.150 mol dm^-3 propanoic acid solution (assume no volume change). Calculate the pH of this buffer at 298 K. Give your answer to 2 decimal places. (3 marks)

  (Total for Question SECTION-A2 is 7 marks)
• 3

  Question SECTION-A3 (8 marks)

  The following equilibrium is established when hydrogen and iodine vapour are heated in a sealed container at 700 K: H2(g) + I2(g) <=> 2HI(g) deltaH = -9.6 kJ mol^-1 A mixture initially containing 0.800 mol H2 and 0.800 mol I2 (and no HI) is allowed to reach equilibrium in a 2.00 dm^3 vessel at 700 K. At equilibrium, 1.20 mol of HI is present. (a) Write the expression for Kc for this equilibrium. (1 mark) (b) Calculate the equilibrium amounts (in mol) of H2 and I2, and hence calculate the value of Kc at 700 K. State why Kc has no units here. (4 marks) (c) State and explain the effect on the value of Kc, and on the equilibrium yield of HI, of increasing the temperature to 900 K. (2 marks)

  (Total for Question SECTION-A3 is 8 marks)
• 4

  Question SECTION-A4 (7 marks)

  Compound X has the molecular formula C4H8O and does not decolourise bromine water. X gives an orange precipitate with 2,4-dinitrophenylhydrazine (2,4-DNPH) but gives a NEGATIVE result with Tollens' reagent. (a) Deduce the functional group present in X and, using the evidence, identify X. Give its name and displayed or structural formula. (3 marks) (b) Describe what you would observe when X is warmed with Fehling's solution, and explain your answer. (2 marks) (c) X can be reduced using NaBH4 in aqueous solution. Name the organic product and state the type of reaction occurring. Write an equation using [H] to represent the reducing agent. (2 marks)

  (Total for Question SECTION-A4 is 7 marks)
• 5

  Question SECTION-A5 (7 marks)

  The rate of the reaction between substances P and Q was investigated at constant temperature: P + 2Q -> R The following initial-rate data were obtained. Experiment 1: [P] = 0.10, [Q] = 0.10, initial rate = 2.0 x 10^-4 mol dm^-3 s^-1 Experiment 2: [P] = 0.20, [Q] = 0.10, initial rate = 4.0 x 10^-4 mol dm^-3 s^-1 Experiment 3: [P] = 0.20, [Q] = 0.30, initial rate = 3.6 x 10^-3 mol dm^-3 s^-1 (All concentrations in mol dm^-3.) (a) Determine the order of reaction with respect to P and with respect to Q. Show your reasoning. (3 marks) (b) Write the overall rate equation and calculate the value of the rate constant k, stating its units. (3 marks) (c) State one possible reason why the order with respect to Q may differ from its stoichiometric coefficient in the overall equation. (1 mark)

  (Total for Question SECTION-A5 is 7 marks)
• 6

  Question SECTION-A6 (8 marks)

  This question is about entropy and reaction feasibility. Consider the thermal decomposition of calcium carbonate: CaCO3(s) -> CaO(s) + CO2(g) deltaH = +178 kJ mol^-1 Standard molar entropies (S, in J K^-1 mol^-1): CaCO3(s) = 92.9; CaO(s) = 39.7; CO2(g) = 213.7. (a) Calculate the standard entropy change, deltaS, for this reaction and comment on the sign of your answer. (3 marks) (b) Calculate the temperature (in K) above which this reaction becomes feasible. (3 marks) (c) State one assumption you made in the calculation in part (b). (2 marks)

  (Total for Question SECTION-A6 is 8 marks)
• 7

  Question SECTION-A7 (7 marks)

  Benzene undergoes electrophilic substitution reactions. (a) Nitration of benzene is carried out using a mixture of concentrated nitric acid and concentrated sulfuric acid at about 50 degrees C. Write an equation showing the formation of the electrophile NO2^+ from the two acids. (2 marks) (b) Outline the mechanism for the nitration of benzene by NO2^+. Show the structure of the intermediate and any curly arrows, and show the regeneration of the catalyst. (3 marks) (c) Explain why benzene undergoes substitution rather than addition reactions, referring to the stability of the delocalised ring. (2 marks)

  (Total for Question SECTION-A7 is 7 marks)
• 8

  Question SECTION-A8 (7 marks)

  A student carries out a redox titration to find the concentration of iron(II) ions in a solution of an iron supplement. A 25.0 cm^3 sample of the iron(II) solution is acidified with dilute sulfuric acid and titrated against 0.0200 mol dm^-3 potassium manganate(VII) solution. The mean titre is 24.60 cm^3. The ionic equation is: MnO4^- + 8H^+ + 5Fe^2+ -> Mn^2+ + 4H2O + 5Fe^3+ (a) State the colour change at the end point and explain why no indicator is needed. (2 marks) (b) Calculate the concentration of Fe^2+ ions, in mol dm^-3, in the supplement solution. (3 marks) (c) Explain why dilute hydrochloric acid should NOT be used to acidify the solution in this titration. (2 marks)

  (Total for Question SECTION-A8 is 7 marks)
• 9

  Question SECTION-A9 (8 marks)

  Alkenes are important intermediates in the petrochemical industry. But-1-ene, CH3CH2CH=CH2, reacts with hydrogen bromide, HBr. (a) Outline the mechanism for the reaction of but-1-ene with HBr to give the major product. Include curly arrows, the structure of the intermediate, and the name of the mechanism. (4 marks) (b) State and explain, using Markovnikov's rule and carbocation stability, why one product forms in a greater amount than the other. (3 marks) (c) Give the name of the minor organic product formed. (1 mark)

  (Total for Question SECTION-A9 is 8 marks)
• 10

  Question SECTION-A10 (7 marks)

  This question concerns the shapes of molecules and intermolecular forces. (a) Predict and state the shape and bond angle of the following molecules/ions, explaining each in terms of electron pairs: (i) BF3; (ii) NH4^+; (iii) SF6. (4 marks) (b) Explain why the boiling point of ammonia, NH3 (-33 degrees C), is much higher than that of phosphine, PH3 (-88 degrees C), even though PH3 has more electrons. (3 marks)

  (Total for Question SECTION-A10 is 7 marks)

Section B

Extended response and synoptic questions. Answer ALL questions.

• 1

  Question SECTION-B1 (11 marks)

  This question is about an electrochemical cell and its thermodynamics. A cell is constructed by connecting a standard nickel half-cell to a standard silver half-cell: Ni^2+(aq) + 2e^- <=> Ni(s) E = -0.25 V Ag^+(aq) + e^- <=> Ag(s) E = +0.80 V (a) Write the conventional cell diagram (cell representation) for this cell and identify the positive electrode. (3 marks) (b) Deduce the overall spontaneous cell reaction and calculate the standard cell EMF. (3 marks) (c) Explain what would happen to the cell EMF if the concentration of Ag^+ ions in the silver half-cell were decreased from 1.00 mol dm^-3 to 0.010 mol dm^-3. Justify your answer using Le Chatelier's principle applied to the silver half-equation. (3 marks) (d) State TWO conditions that must be specified for a standard electrode potential to be measured. (2 marks)

  (Total for Question SECTION-B1 is 11 marks)
• 2

  Question SECTION-B2 (10 marks)

  This question is about organic synthesis and analysis. Compound A is an aromatic ester with molecular formula C9H10O2. On heating A under reflux with aqueous sodium hydroxide, followed by acidification, two products are obtained: compound B, which is found to be benzoic acid (C6H5COOH); and compound C, which is an alcohol. (a) Deduce the structure of C and hence the full structural formula of ester A, and give the name of A. (3 marks) (b) Write the balanced equation for the hydrolysis of A with aqueous NaOH (before acidification), giving the sodium salt of B and alcohol C. (2 marks) (c) Compound C can be oxidised by acidified potassium dichromate(VI). State the reagents and conditions to oxidise C fully to a carboxylic acid, name that carboxylic acid, and give the colour change observed. (3 marks) (d) Describe a simple chemical test, with the expected observation, that would distinguish benzoic acid (B) from the alcohol (C). (2 marks)

  (Total for Question SECTION-B2 is 10 marks)
• 3

  Question SECTION-B3 (11 marks)

  This question is about the transition metal chemistry of copper and its complexes. When aqueous ammonia is added dropwise, and then in excess, to a solution containing [Cu(H2O)6]^2+ ions, a series of changes is observed. (a) Describe what is seen when a small amount of aqueous ammonia is added, and write an equation for the reaction. Name the type of reaction. (3 marks) (b) On adding excess aqueous ammonia, the precipitate dissolves to give a deep blue solution containing [Cu(NH3)4(H2O)2]^2+. Write an equation for this reaction and name the type of reaction taking place. Explain why only four of the six water ligands are replaced. (4 marks) (c) Explain, in terms of d-orbitals and electron transitions, why [Cu(H2O)6]^2+ is coloured. In your answer refer to d-orbital splitting, the frequency/wavelength of light absorbed, and how the colour observed relates to the light absorbed. (5 marks)

  (Total for Question SECTION-B3 is 11 marks)