OCR A-Level Chemistry 2027 Predicted Practice Paper — Periodic Table, Elements and Physical Chemistry

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

Section A

Multiple choice. Answer ALL the questions.

• 1

  Question SECTION-A1 (1 mark)

  Which electron configuration represents a Cr^3+ ion in its ground state? (Cr has atomic number 24)

  A. [Ar] 3d^3B. [Ar] 3d^1 4s^2C. [Ar] 3d^5 4s^1D. [Ar] 3d^2 4s^1

  (Total for Question SECTION-A1 is 1 mark)
• 2

  Question SECTION-A2 (1 mark)

  A sample of an element consists of 60% of an isotope with mass 68 and 40% of an isotope with mass 70. What is the relative atomic mass of the element?

  A. 68.4B. 68.8C. 69.0D. 69.2

  (Total for Question SECTION-A2 is 1 mark)
• 3

  Question SECTION-A3 (1 mark)

  Which of the following molecules has a trigonal pyramidal shape?

  A. BF3B. NH3C. CH4D. CO2

  (Total for Question SECTION-A3 is 1 mark)
• 4

  Question SECTION-A4 (1 mark)

  Which statement about a reaction that has reached dynamic equilibrium in a closed system is correct?

  A. The forward reaction has stoppedB. The concentrations of reactants and products are equalC. The rate of the forward reaction equals the rate of the reverse reactionD. The activation energy of the forward reaction is zero

  (Total for Question SECTION-A4 is 1 mark)
• 5

  Question SECTION-A5 (1 mark)

  What is the oxidation number of chlorine in the chlorate(V) ion, ClO3^-?

  A. +3B. +5C. +6D. +7

  (Total for Question SECTION-A5 is 1 mark)
• 6

  Question SECTION-A6 (1 mark)

  Which reagent and conditions convert propan-1-ol into propanoic acid?

  A. Acidified potassium dichromate(VI), distilled off immediatelyB. Acidified potassium dichromate(VI), heated under refluxC. Concentrated sulfuric acid, heatedD. Sodium metal at room temperature

  (Total for Question SECTION-A6 is 1 mark)
• 7

  Question SECTION-A7 (1 mark)

  Which halogenoalkane undergoes nucleophilic substitution with aqueous hydroxide ions most rapidly?

  A. 1-chlorobutaneB. 1-bromobutaneC. 1-iodobutaneD. 1-fluorobutane

  (Total for Question SECTION-A7 is 1 mark)
• 8

  Question SECTION-A8 (1 mark)

  A first-order reaction has a rate constant k. Which of the following statements is correct about its half-life?

  A. The half-life doubles as the reaction proceedsB. The half-life is independent of the initial concentrationC. The half-life increases with increasing temperatureD. The half-life is equal to 1/k regardless of order

  (Total for Question SECTION-A8 is 1 mark)
• 9

  Question SECTION-A9 (1 mark)

  Which of the following aqueous solutions, all at 0.10 mol dm^-3, has the lowest pH?

  A. Ethanoic acidB. Hydrochloric acidC. AmmoniaD. Sodium hydroxide

  (Total for Question SECTION-A9 is 1 mark)
• 10

  Question SECTION-A10 (1 mark)

  For the equilibrium N2(g) + 3H2(g) <=> 2NH3(g), the forward reaction is exothermic. Which change increases the equilibrium yield of ammonia?

  A. Increasing temperatureB. Decreasing pressureC. Increasing pressureD. Adding a catalyst

  (Total for Question SECTION-A10 is 1 mark)
• 11

  Question SECTION-A11 (1 mark)

  Which species acts as a Bronsted-Lowry base in the reaction HNO3 + H2O -> H3O^+ + NO3^-?

  A. HNO3B. H2OC. H3O^+D. NO3^-

  (Total for Question SECTION-A11 is 1 mark)
• 12

  Question SECTION-A12 (1 mark)

  Which of these compounds exhibits E/Z (cis-trans) isomerism?

  A. But-1-eneB. 2-methylpropeneC. But-2-eneD. Propene

  (Total for Question SECTION-A12 is 1 mark)
• 13

  Question SECTION-A13 (1 mark)

  The standard electrode potentials are: Zn^2+/Zn = -0.76 V and Cu^2+/Cu = +0.34 V. What is the standard cell potential of the cell made from these two half-cells?

  A. +0.42 VB. +1.10 VC. -1.10 VD. -0.42 V

  (Total for Question SECTION-A13 is 1 mark)
• 14

  Question SECTION-A14 (1 mark)

  Which technique is most appropriate for determining the relative molecular mass of an unknown organic compound?

  A. Infrared spectroscopyB. Mass spectrometryC. Carbon-13 NMR spectroscopyD. Ultraviolet-visible spectroscopy

  (Total for Question SECTION-A14 is 1 mark)
• 15

  Question SECTION-A15 (1 mark)

  Which of the following would produce a buffer solution?

  A. Mixing equal volumes of 0.1 mol dm^-3 HCl and 0.1 mol dm^-3 NaOHB. Mixing 0.1 mol dm^-3 ethanoic acid with 0.1 mol dm^-3 sodium ethanoateC. Mixing 0.1 mol dm^-3 HCl with 0.1 mol dm^-3 NaClD. Dissolving sodium chloride in water

  (Total for Question SECTION-A15 is 1 mark)

Section B

Structured and extended response questions. Answer ALL the questions.

• 1

  Question SECTION-B1 (8 marks)

  Ammonia is manufactured industrially by the Haber process: N2(g) + 3H2(g) <=> 2NH3(g), delta H = -92 kJ mol^-1. (a) State and explain, in terms of Le Chatelier's principle, the effect of increasing temperature on the equilibrium yield of ammonia. (3 marks) (b) Typical industrial conditions are 450 degrees C, 200 atm and an iron catalyst. Explain why a temperature of 450 degrees C is used rather than a lower temperature that would give a higher equilibrium yield. (2 marks) (c) Explain why the iron catalyst does not change the equilibrium yield of ammonia but is still used. (3 marks)

  (Total for Question SECTION-B1 is 8 marks)
• 2

  Question SECTION-B2 (8 marks)

  Butanoic acid, CH3CH2CH2COOH, is a weak acid with Ka = 1.5 x 10^-5 mol dm^-3 at 298 K. (a) Write an expression for Ka for butanoic acid. (1 mark) (b) Calculate the pH of a 0.150 mol dm^-3 solution of butanoic acid. (3 marks) (c) A buffer is prepared by mixing 50.0 cm^3 of 0.150 mol dm^-3 butanoic acid with 50.0 cm^3 of 0.100 mol dm^-3 sodium butanoate. Calculate the pH of this buffer. (4 marks)

  (Total for Question SECTION-B2 is 8 marks)
• 3

  Question SECTION-B3 (9 marks)

  This question concerns the Born-Haber cycle for potassium chloride, KCl. Use the following data (all in kJ mol^-1): enthalpy of atomisation of K = +89; first ionisation energy of K = +419; enthalpy of atomisation of Cl = +122; first electron affinity of Cl = -349; enthalpy of formation of KCl = -437. (a) Define the term lattice enthalpy of formation. (2 marks) (b) Construct the Born-Haber cycle and calculate the lattice enthalpy of formation of KCl. (4 marks) (c) State and explain how the lattice enthalpy of formation of potassium chloride would compare with that of potassium bromide. (3 marks)

  (Total for Question SECTION-B3 is 9 marks)
• 4

  Question SECTION-B4 (8 marks)

  An organic compound X has the molecular formula C4H8O. It does not react with Fehling's solution or Tollens' reagent, but it does form an orange precipitate with 2,4-dinitrophenylhydrazine (2,4-DNPH). (a) Identify the functional group present in X and justify your answer using the observations above. (3 marks) (b) Give the structural formula and name of a possible structure for X. (2 marks) (c) X can be reduced using sodium borohydride (NaBH4). Give the structural formula of the organic product and name the type of reaction. (2 marks) (d) State, with a reason, whether the reduction product from part (c) shows optical isomerism. (1 mark)

  (Total for Question SECTION-B4 is 8 marks)
• 5

  Question SECTION-B5 (7 marks)

  The rate of the reaction between substance P and substance Q was investigated at constant temperature. The results are shown below. 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 = 8.0 x 10^-4 mol dm^-3 s^-1. Experiment 3: [P] = 0.20, [Q] = 0.20, initial rate = 8.0 x 10^-4 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, showing your reasoning. (3 marks) (b) Write the rate equation and state the overall order of reaction. (2 marks) (c) Calculate the value of the rate constant k, including its units. (2 marks)

  (Total for Question SECTION-B5 is 7 marks)
• 6

  Question SECTION-B6 (9 marks)

  Transition metal ions form coloured complexes in aqueous solution. (a) Explain, in terms of electrons and d orbitals, why aqueous solutions of copper(II) ions are coloured. (3 marks) (b) When concentrated hydrochloric acid is added to a pale blue solution containing [Cu(H2O)6]^2+ ions, the solution turns yellow-green as a new complex forms. Write an equation for this ligand substitution reaction and state the shape and coordination number of the product. (3 marks) (c) Explain what is meant by the term 'ligand' and why the chloride ligand and the water ligand give complexes of different colours. (3 marks)

  (Total for Question SECTION-B6 is 9 marks)
• 7

  Question SECTION-B7 (8 marks)

  2-bromobutane can undergo two different types of reaction depending on the conditions used. (a) When 2-bromobutane is warmed with aqueous sodium hydroxide, a substitution reaction occurs. Draw the mechanism using curly arrows and name the mechanism. (4 marks) (b) When 2-bromobutane is heated with ethanolic (in ethanol) sodium hydroxide, an elimination reaction occurs. Name and give the structural formulae of the TWO isomeric alkene products (excluding E/Z isomers). (2 marks) (c) State the role of the hydroxide ion in each of the two reactions. (2 marks)

  (Total for Question SECTION-B7 is 8 marks)
• 8

  Question SECTION-B8 (7 marks)

  The concentration of iron(II) ions in a solution can be found by titration with acidified potassium manganate(VII), KMnO4. The half-equations are: MnO4^- + 8H^+ + 5e^- -> Mn^2+ + 4H2O Fe^2+ -> Fe^3+ + e^- (a) Construct the overall balanced ionic equation for the reaction. (2 marks) (b) In a titration, 25.0 cm^3 of an iron(II) solution required 22.4 cm^3 of 0.0200 mol dm^-3 KMnO4 for complete reaction. Calculate the concentration of iron(II) ions in the solution, in mol dm^-3. (4 marks) (c) State why no indicator is needed in this titration and describe the colour change at the end point. (1 mark)

  (Total for Question SECTION-B8 is 7 marks)
• 9

  Question SECTION-B9 (8 marks)

  Nitrogen monoxide and ozone react in the atmosphere: NO(g) + O3(g) -> NO2(g) + O2(g). For this calculation use the following simplified bonding model and mean bond enthalpies (in kJ mol^-1): N=O = 587, N-O = 214, O=O = 498, O-O = 146. Model NO as containing one N=O bond; O3 as containing one O=O bond and one O-O bond; NO2 as containing one N=O bond and one N-O bond; and O2 as containing one O=O bond. (a) Using this model, estimate the enthalpy change of the reaction, clearly showing the bonds broken and the bonds formed. (5 marks) (b) State whether the reaction is exothermic or endothermic and relate this to the sign of your calculated value. (1 mark) (c) Explain why values calculated from mean bond enthalpies are only approximate. (2 marks)

  (Total for Question SECTION-B9 is 8 marks)
• 10

  Question SECTION-B10 (6 marks)

  Alkenes are important intermediates in industrial synthesis. (a) Describe the mechanism of the electrophilic addition of hydrogen bromide (HBr) to propene, using curly arrows, and explain why the major product is 2-bromopropane rather than 1-bromopropane. (4 marks) (b) Name the type of intermediate formed and explain, in terms of its stability, why it leads to the major product. (2 marks)

  (Total for Question SECTION-B10 is 6 marks)
• 11

  Question SECTION-B11 (7 marks)

  This question is about electrochemical cells and standard electrode potentials. Use the following standard electrode potentials: Ag^+(aq) + e^- -> Ag(s), E = +0.80 V Fe^3+(aq) + e^- -> Fe^2+(aq), E = +0.77 V Ni^2+(aq) + 2e^- -> Ni(s), E = -0.25 V (a) Define the term standard electrode potential. (2 marks) (b) A cell is constructed from the Ag^+/Ag half-cell and the Ni^2+/Ni half-cell. Calculate the standard cell potential and write the overall cell reaction that occurs spontaneously. (3 marks) (c) Predict, with a reason, whether Fe^3+ ions will oxidise nickel metal under standard conditions. (2 marks)

  (Total for Question SECTION-B11 is 7 marks)