plumiRedox titrations and calculations: OCR A‑Level Chemistry A questions
OCR A-Level Chemistry A past-paper questions on 5.2.3.2 Redox titrations and calculations, 2016–2025, with mark schemes and examiner’s reports where available.
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Q21(d)(i)
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All 27 questions on Redox titrations and calculations, as a list
- June 2025, Paper 1, Q21(d)(i) (5 marks): Calculate the percentage by mass of CuSO4•5H2O in Mixture A. Give your answer to 3 significant figures. Percentage of CuSO4•5H2O in Mixture A = % [5]
- June 2025, Paper 1, Q21(d)(ii) (1 mark): The student repeats their method, but after carrying out Step 1 they leave the solution exposed to the air for a few days. Some of the iron(II) sulfate is oxidi
- June 2024, Paper 1, Q21(b) (4 marks): Potassium iodate tablets prevent the uptake of radioactive iodine in the human body following a nuclear accident. The mass of potassium iodate(V), KIO3, in a ta
- June 2024, Paper 3, Q3(b)(i) (2 marks): In the titration, both iron(II) ions and ethanedioate, C2O4 Construct half-equations for the oxidation of iron(II) and ethanedioate ions. Oxidation of iron(II)
- June 2024, Paper 3, Q3(b)(ii) (3 marks): The student prepares a 250.0 cm3 solution of iron(II) ethanedioate by dissolving 1.295 g of FeC2O4•xH2O, in dilute sulfuric acid. The student titrates 25.0 cm3
- June 2024, Paper 3, Q3(b)(iii) (1 mark): The uncertainty in each burette reading is ±0.05 cm3. Calculate the percentage uncertainty for the titre in Titration 1. percentage uncertainty = % [1]
- June 2024, Paper 3, Q3(b)(iv) (6 marks): This question is about compounds and ions of iron(II) and iron(III) that contain ethanedioate ions, 2–. C2O4 (iv)* In the titration, 5 mol of iron(II) ethanedio
- June 2023, Paper 1, Q21(a)(i) (1 mark): State the colour change seen at the end point of the titration. from to [1]
- June 2023, Paper 1, Q21(a)(ii) (2 marks): The student’s titration results are shown in the table below. The trial titre has been omitted. 1 2 3 Final volume / cm3 12.65 25.60 38.35 Initial volume / cm3
- June 2023, Paper 1, Q21(a)(iii) (3 marks): Determine the concentration, in mol dm–3, of iron(II) ions in the river water. concentration = mol dm–3 [3]
- June 2023, Paper 1, Q21(b) (4 marks): The student modifies the experiment in (a) to determine the combined concentration of iron(II) and iron(III) ions in the river water. The student’s method is sh
- June 2022, Paper 1, Q4 (1 mark): Hydrogen peroxide, H2O2, can be oxidised by manganate(VII) ions under acid conditions as shown below. –(aq) + 5H2O2(aq) + 6H+(aq) 2Mn2+(aq) + 5O2(g) + 8H2O(l) 2
- June 2022, Paper 3, Q6(d) (4 marks): The label on a carton of orange juice lists the mass of vitamin C, in mg, in a typical serving of 150 cm3. The student carries out an investigation to check the
- November 2021, Paper 1, Q18(c) (1 mark): Suggest a suitable indicator for this titration and state the colour change at the end point in Step 4. Indicator: Colour from to [1]
- November 2021, Paper 1, Q18(d) (4 marks): Determine the percentage, by mass, of copper in the copper ore. Give your answer to an appropriate number of significant figures. percentage = % [4]
- November 2021, Paper 1, Q18(e)(i) (1 mark): The potassium iodide was not in excess, in Step 3. [1]
- November 2021, Paper 1, Q18(e)(ii) (1 mark): The burette readings were read from the top of the meniscus, in Step 4. [1]
- November 2021, Paper 1, Q18(f) (2 marks): The student then modifies the method in order to obtain a more accurate value for the percentage by mass of copper in the ore. The student decides to use 25.00
- November 2020, Paper 1, Q22(c) (5 marks): Sodium sulfite(IV), Na2SO3, is used as a preservative in some foods. Food safety legislation allows a maximum of 850 mg Na2SO3 per kg of burger meat. A chemist
- June 2019, Paper 1, Q18(c)(i) (1 mark): Explain why the student used 0.00200 mol dm−3 potassium manganate(VII) solution for this titration, rather than the more usual concentration of 0.0200 mol dm−3
- June 2019, Paper 1, Q18(c)(ii) (5 marks): Use the student’s results to determine the mass, in mg, of iron(II) gluconate in one tablet. Give your answer to 3 significant figures. mass of iron(II) glucona
- June 2018, Paper 1, Q20(d)(i) (2 marks): Complete Table 20.1 and calculate the mean titre that the student should use for analysing the results. mean titre = cm3 [2]
- June 2018, Paper 1, Q20(d)(ii) (1 mark): The uncertainty in each burette reading is ±0.05 cm3. Calculate the percentage uncertainty in the titre obtained from titration 1. Give your answer to two decim
- June 2018, Paper 1, Q20(d)(iii) (2 marks): Describe and explain how the student should determine the end point of this titration accurately. [2]
- June 2018, Paper 1, Q20(d)(iv) (5 marks): Determine the relative formula mass and formula of the Group 1 iodate(V), B. Show your working. relative formula mass of B = formula of B = [5]
- June 2018, Paper 3, Q3(b)(i) (1 mark): This titration is self-indicating and the student does not need to add an indicator. What colour change would the student observe at the end point? Colour chang
- June 2018, Paper 3, Q3(b)(ii) (6 marks): Calculate the percentage, by mass, of ethanedioic acid in the rhubarb leaves. Give your answer to an appropriate number of significant figures. percentage of et
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