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Redox: OCR A‑Level Chemistry A questions

Every OCR A-Level Chemistry A exam question on 2.1.5 Redox, 2016–2025, with its mark scheme and examiner’s report.

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1,820 questions

  1. Q19(b)(ii)

    June 2025 · Paper 1

    3 marks2.1.5 Redox
    The whole paper ↗
    June 2025 Paper 1, question 19(b)(ii): When heated, aqueous HNO2 disproportionates. The equation is shown below. 3HNO2(aq) HNO3(aq) + 2NO(g) + H2O(l) • What is meant by disproportionation? • Use oxid

  2. Q4(a)(i)

    June 2025 · Paper 3

    1 mark2.1.5 Redox
    The whole paper ↗
    June 2025 Paper 3, question 4(a)(i): What is the systematic name of a SO3 [1]

  3. Q6

    June 2025 · AS Paper 1

    1 mark2.1.5 Redox
    The whole paper ↗
    June 2025 AS Paper 1, question 6: What is the oxidation number of S in Na2S2O3? A –4 B –2 C +2 D +4 Your answer [1]

  4. Q7

    June 2025 · AS Paper 1

    1 mark2.1.5 Redox
    The whole paper ↗
    June 2025 AS Paper 1, question 7: Which of the following is not a redox reaction? A CH4(g) + 2O2(g) CO2(g) + 2H2O(l) B NaOH(aq) + HCl (aq) NaCl (aq) + H2O(l) C 2KCl O3(s) 2KCl (s) + 3O2(g) D Fe(

  5. Q16(b)(iii)

    June 2024 · Paper 1

    1 mark2.1.5 Redox
    The whole paper ↗
    June 2024 Paper 1, question 16(b)(iii): Mn3O4 is a compound in which Mn has two different oxidation states. The two oxidation states are different from the Mn in MnO2. Suggest the two oxidation states

  6. Q4(a)(iii)

    June 2024 · Paper 3

    1 mark2.1.5 Redox
    The whole paper ↗
    June 2024 Paper 3, question 4(a)(iii): The systematic name of H3PO4 is phosphoric(V) acid. What is the systematic name of H3PO3? [1]

  7. Q4(b)(ii)

    June 2024 · Paper 3

    3 marks2.1.5 Redox
    The whole paper ↗
    June 2024 Paper 3, question 4(b)(ii): Aqueous silver nitrate, AgNO3, is reduced by PH3. The unbalanced equation is shown below. Balance the equation and use oxidation numbers to explain why this is

  8. Q21(b)(i)

    June 2024 · AS Paper 1

    1 mark2.1.5 Redox
    The whole paper ↗
    June 2024 AS Paper 1, question 21(b)(i): What is the systematic name for Fe2O3? [1]

  9. Q2(b)(i)

    June 2024 · AS Paper 2

    2 marks2.1.5 Redox
    The whole paper ↗
    June 2024 AS Paper 2, question 2(b)(i): Explain, in terms of electron transfer, why the reaction shown in equation 2.1 is a redox reaction. [2]

  10. Q2(a)(i)

    June 2023 · Paper 3

    1 mark2.1.5 Redox
    The whole paper ↗
    June 2023 Paper 3, question 2(a)(i): The oxidation number of chlorine is different in the two rubidium salts, RbCl O3 and RbCl O4. What is the name of RbCl O4? [1]

  11. Q5

    June 2023 · AS Paper 1

    1 mark2.1.5 Redox
    The whole paper ↗
    June 2023 AS Paper 1, question 5: Which substance has the lowest oxidation number for sulfur? A Na2SO4 B S8 C SF2 D SO2 Your answer [1]

  12. Q1(b)(i)

    June 2023 · AS Paper 2

    1 mark2.1.5 Redox
    The whole paper ↗
    June 2023 AS Paper 2, question 1(b)(i): The common name for TiO2 is titanium dioxide. What is the systematic name of TiO2? [1]

  13. Q6

    June 2022 · Paper 1

    1 mark2.1.5 Redox
    The whole paper ↗
    June 2022 Paper 1, question 6: Prussian blue, C18Fe7N18, is a deep blue pigment containing Fe2+, Fe3+ and CN− ions. 6 What are the numbers of Fe2+ and Fe3+ ions in one formula unit of C18Fe7N

  14. Q21(a)(ii)

    June 2022 · Paper 1

    2 marks2.1.5 Redox
    The whole paper ↗
    June 2022 Paper 1, question 21(a)(ii): Write half-equations for the reaction of magnesium with hydrochloric acid. Oxidation half-equation: Reduction half-equation: [2]

  15. Q1(a)(ii)

    June 2022 · Paper 3

    1 mark2.1.5 Redox
    The whole paper ↗
    June 2022 Paper 3, question 1(a)(ii): Two students discuss the oxidation numbers in ammonium nitrate, NH4NO3. One student claims that the two nitrogen atoms have the same oxidation number. The other

  16. Q2(a)(ii)

    June 2022 · Paper 3

    3 marks2.1.5 Redox
    The whole paper ↗
    June 2022 Paper 3, question 2(a)(ii): Calcium hypochlorite, Ca(Cl O)2, is heated. The Ca(Cl O)2 decomposes to form CaCl 2 and Ca(Cl O3)2. This is a disproportionation reaction. Write an equation for

  17. Q23(b)

    June 2022 · AS Paper 1

    2 marks2.1.5 Redox
    The whole paper ↗
    June 2022 AS Paper 1, question 23(b): ‘Oxyanions’ are ions containing oxygen combined with atoms of other elements. Roman numerals are used to show the oxidation state of the element in the oxyanion

  18. Q2

    November 2021 · Paper 1

    1 mark2.1.5 Redox
    The whole paper ↗
    November 2021 Paper 1, question 2: A chlorate(VII) ion has a 1– charge. What is the formula for sodium chlorate(VII)? A NaCl O3 B NaCl O4 C NaCl O7 D NaCl O8 Your answer [1]

  19. Q19(b)(i)

    November 2021 · Paper 1

    2 marks2.1.5 Redox
    The whole paper ↗
    November 2021 Paper 1, question 19(b)(i): Explain, in terms of oxidation numbers, why disproportionation has taken place. [2]

  20. Q23(b)

    November 2021 · AS Paper 1

    2 marks2.1.5 Redox
    The whole paper ↗
    November 2021 AS Paper 1, question 23(b): Chlorine can be prepared by reacting concentrated hydrochloric acid with manganese(IV) oxide, MnO2. 4HCl (aq) + MnO2(s) → Cl 2(g) + MnCl 2(aq) + 2H2O(l) Using o
All 48 questions on Redox, as a list
  1. June 2025, Paper 1, Q19(b)(ii) (3 marks): When heated, aqueous HNO2 disproportionates. The equation is shown below. 3HNO2(aq) HNO3(aq) + 2NO(g) + H2O(l) • What is meant by disproportionation? • Use oxid
  2. June 2025, Paper 3, Q4(a)(i) (1 mark): What is the systematic name of a SO3 [1]
  3. June 2025, AS Paper 1, Q6 (1 mark): What is the oxidation number of S in Na2S2O3? A –4 B –2 C +2 D +4 Your answer [1]
  4. June 2025, AS Paper 1, Q7 (1 mark): Which of the following is not a redox reaction? A CH4(g) + 2O2(g) CO2(g) + 2H2O(l) B NaOH(aq) + HCl (aq) NaCl (aq) + H2O(l) C 2KCl O3(s) 2KCl (s) + 3O2(g) D Fe(
  5. June 2024, Paper 1, Q16(b)(iii) (1 mark): Mn3O4 is a compound in which Mn has two different oxidation states. The two oxidation states are different from the Mn in MnO2. Suggest the two oxidation states
  6. June 2024, Paper 3, Q4(a)(iii) (1 mark): The systematic name of H3PO4 is phosphoric(V) acid. What is the systematic name of H3PO3? [1]
  7. June 2024, Paper 3, Q4(b)(ii) (3 marks): Aqueous silver nitrate, AgNO3, is reduced by PH3. The unbalanced equation is shown below. Balance the equation and use oxidation numbers to explain why this is
  8. June 2024, AS Paper 1, Q21(b)(i) (1 mark): What is the systematic name for Fe2O3? [1]
  9. June 2024, AS Paper 2, Q2(b)(i) (2 marks): Explain, in terms of electron transfer, why the reaction shown in equation 2.1 is a redox reaction. [2]
  10. June 2023, Paper 3, Q2(a)(i) (1 mark): The oxidation number of chlorine is different in the two rubidium salts, RbCl O3 and RbCl O4. What is the name of RbCl O4? [1]
  11. June 2023, AS Paper 1, Q5 (1 mark): Which substance has the lowest oxidation number for sulfur? A Na2SO4 B S8 C SF2 D SO2 Your answer [1]
  12. June 2023, AS Paper 2, Q1(b)(i) (1 mark): The common name for TiO2 is titanium dioxide. What is the systematic name of TiO2? [1]
  13. June 2022, Paper 1, Q6 (1 mark): Prussian blue, C18Fe7N18, is a deep blue pigment containing Fe2+, Fe3+ and CN− ions. 6 What are the numbers of Fe2+ and Fe3+ ions in one formula unit of C18Fe7N
  14. June 2022, Paper 1, Q21(a)(ii) (2 marks): Write half-equations for the reaction of magnesium with hydrochloric acid. Oxidation half-equation: Reduction half-equation: [2]
  15. June 2022, Paper 3, Q1(a)(ii) (1 mark): Two students discuss the oxidation numbers in ammonium nitrate, NH4NO3. One student claims that the two nitrogen atoms have the same oxidation number. The other
  16. June 2022, Paper 3, Q2(a)(ii) (3 marks): Calcium hypochlorite, Ca(Cl O)2, is heated. The Ca(Cl O)2 decomposes to form CaCl 2 and Ca(Cl O3)2. This is a disproportionation reaction. Write an equation for
  17. June 2022, AS Paper 1, Q23(b) (2 marks): ‘Oxyanions’ are ions containing oxygen combined with atoms of other elements. Roman numerals are used to show the oxidation state of the element in the oxyanion
  18. November 2021, Paper 1, Q2 (1 mark): A chlorate(VII) ion has a 1– charge. What is the formula for sodium chlorate(VII)? A NaCl O3 B NaCl O4 C NaCl O7 D NaCl O8 Your answer [1]
  19. November 2021, Paper 1, Q19(b)(i) (2 marks): Explain, in terms of oxidation numbers, why disproportionation has taken place. [2]
  20. November 2021, AS Paper 1, Q23(b) (2 marks): Chlorine can be prepared by reacting concentrated hydrochloric acid with manganese(IV) oxide, MnO2. 4HCl (aq) + MnO2(s) → Cl 2(g) + MnCl 2(aq) + 2H2O(l) Using o
  21. November 2020, Paper 1, Q18(a) (3 marks): A student adds magnesium metal to an aqueous solution of ethanoic acid, CH3COOH. A redox reaction takes place. Write the overall equation for this reaction and
  22. November 2020, Paper 1, Q22(b)(ii) (1 mark): Determine the oxidation number of nickel in compound J. oxidation number: [1]
  23. November 2020, Paper 3, Q4(a)(i) (3 marks): In Stage 1, a redox reaction takes place between M and HCl (aq), forming hydrogen and a solution containing M in the +2 oxidation state. Write an overall equati
  24. November 2020, Paper 3, Q4(a)(ii) (2 marks): In Stage 1, suggest two observations that would confirm that all of metal M has reacted. 1 2 [2]
  25. November 2020, AS Paper 1, Q6 (1 mark): The equation for a redox reaction is shown below. 2HCl O3 + 2HCl → 2Cl O2 + Cl 2 + 2H2O Which statement is correct? A Cl is both oxidised and reduced. B Cl is o
  26. November 2020, AS Paper 1, Q7 (1 mark): Potassium ferrate(VI) contains two potassium ions for every ferrate(VI) ion. What is the formula of the ferrate(VI) ion? 2− A FeO3 2− B FeO4 2− C FeO5 2− D FeO6
  27. November 2020, AS Paper 2, Q1(a) (1 mark): Nickel reacts with dilute hydrochloric acid in a redox reaction. Ni(s) + 2HCl (aq) NiCl 2(aq) + H2(g) Explain, in terms of the number of electrons transferred,
  28. November 2020, AS Paper 2, Q3(d)(i) (1 mark): Write the systematic name for NaBrO3. [1]
  29. June 2019, Paper 1, Q5 (1 mark): What is the oxidation number of N in Mg(NO2)2•3H2O? A +2 B +3 C +4 D +5 Your answer [1]
  30. June 2019, Paper 1, Q6 (1 mark): Which reaction is a redox reaction? A NaCl + AgNO3 AgCl + NaNO3 B NaNO2 + HCl NaCl + HNO2 C CaSO3 + 2HCl CaCl 2 + H2O + SO2 D 3CuO + 2NH3 3Cu + 3H2O + N2 Your a
  31. June 2019, Paper 3, Q6(a)(ii) (1 mark): The student thinks that the reaction of iron(II) sulfide with H+ / H2O is a redox reaction. Explain, with reasons, whether the student is correct. [1]
  32. June 2019, AS Paper 1, Q9 (1 mark): Which reaction shows chlorine only being oxidised? A Cl 2 + H2O → HCl + HCl O B 2Cl O2 + 2NaOH → NaCl O2 + NaCl O3 + H2O C 4KCl O3 → 3KCl O4 + KCl D MnO2 + 4HCl
  33. June 2019, AS Paper 2, Q2(c) (2 marks): Magnesium nitrate decomposes when heated, as shown in the equation. 2Mg(NO3)2(s) 2MgO(s) + 4NO2(g) + O2(g) Using oxidation numbers, show which element has been
  34. June 2018, Paper 1, Q2 (1 mark): In the compound [ICl2]+ [SbCl6]–, the oxidation number of chlorine is –1. 2 What are the oxidation numbers of I and Sb in the compound? I Sb A +1 +5 B +1 +7 C +
  35. June 2018, Paper 3, Q1(a)(vii) (1 mark): An element which forms a compound with hydrogen in which the element has an oxidation number of –4. [1]
  36. June 2018, Paper 3, Q4(a)(i) (1 mark): What is the oxidation number of platinum in cis-platin? [1]
  37. June 2018, AS Paper 1, Q6 (1 mark): What is the oxidation number of Fe in K2FeO4? A +4 B +5 C +6 D +7 Your answer [1]
  38. June 2018, AS Paper 1, Q7 (1 mark): Which reaction shows oxidation of sulfur? A 2HBr + H2SO4 → SO2 + 2H2O + Br2 B SO2 + 2NaOH → Na2SO3 + H2O C 8HI + H2SO4 → 4I2 + H2S + 4H2O D H2S + Cl 2 → 2HCl +
  39. June 2018, AS Paper 1, Q22(a)(i) (1 mark): In terms of the number of electrons transferred, explain whether magnesium is being oxidised or reduced. [1]
  40. June 2017, Paper 1, Q3 (1 mark): What is the oxidation number of Mn in K2MnO4? A +4 B +5 C +6 D +7 Your answer [1]
  41. June 2017, Paper 1, Q17(c)(i) (3 marks): State what is meant by disproportionation and use oxidation numbers to show that disproportionation has taken place. [3]
  42. June 2017, Paper 1, Q17(c)(ii) (1 mark): What is the systematic name for KCl O4? [1]
  43. June 2017, Paper 3, Q2(d)(i) (1 mark): What is the systematic name for NaNO2? [1]
  44. June 2017, Paper 3, Q2(d)(ii) (2 marks): Using oxidation numbers, with signs, show the element that is oxidised and the element that is reduced in this reaction. Element oxidised Oxidation number chang
  45. June 2017, Paper 3, Q2(d)(iii) (1 mark): Construct the equation for this reaction. Equation [1]
  46. June 2017, AS Paper 1, Q24(b)(ii) (2 marks): This reaction is a redox reaction. Deduce which element has been oxidised and which element has been reduced, and state the changes in oxidation number. Element
  47. June 2016, AS Paper 1, Q5 (1 mark): What is the oxidation number of nitrogen in Mg(NO3)2? A –3 B +2 C +5 D +6 Your answer [1]
  48. June 2016, AS Paper 1, Q22(d) (2 marks): Salts can also be prepared in redox reactions of metals with acids. A student prepares a solution of aluminium sulfate by reacting aluminium with dilute sulfuri

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