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Redox I: Edexcel A‑Level Chemistry questions

Every Edexcel A-Level Chemistry exam question on 3 Redox I, 2016–2025, with its mark scheme and examiner’s report.

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2,028 questions

  1. Q6(b)

    June 2025 · AS Paper 1

    1 mark3 Redox I
    The whole paper ↗
    June 2025 AS Paper 1, question 6(b): Which change in oxidation number of sulfur, if any, occurs during the formation of H2S? (1) A from +6 to −2 B from +6 to +2 C from +2 to −2 D no change

  2. Q6(c)

    June 2025 · AS Paper 1

    2 marks3 Redox I
    The whole paper ↗
    June 2025 AS Paper 1, question 6(c): Deduce the two ionic half-equations for this reaction. State symbols are not required. (2) Oxidation half-equation Reduction half-equation

  3. Q3(b)

    June 2024 · Paper 2

    3 marks3 Redox I
    The whole paper ↗
    June 2024 Paper 2, question 3(b): Hydrogen peroxide decomposes to form water and oxygen. 2H2O2(aq) → 2H2O(l) + O2(g) Explain, using oxidation numbers, why the decomposition of hydrogen peroxide

  4. Q4(c)(i)

    June 2024 · Paper 3

    1 mark3 Redox I
    The whole paper ↗
    June 2024 Paper 3, question 4(c)(i): Complete the ionic equation for this redox reaction, using oxidation numbers. State symbols are not required. (1) – + OH– + H2O → Al(OH)4 – + NH3 8Al + NO3

  5. Q5(f)

    June 2024 · AS Paper 1

    1 mark3 Redox I
    The whole paper ↗
    June 2024 AS Paper 1, question 5(f): What is the oxidation number of oxygen in the chlorate(III) ion, ClO2 – ? (1) A −1 B +1 C −2 D +2

  6. Q9(a)

    June 2024 · AS Paper 1

    1 mark3 Redox I
    The whole paper ↗
    June 2024 AS Paper 1, question 9(a): Iodine is reduced by thiosulfate ions. The relevant half‑equations are shown. ½I2 + e– → I– 2– → S4O6 2– + 2e– 2S2O3 Deduce an overall equation for this reactio

  7. Q9(b)(i)

    June 2024 · AS Paper 1

    1 mark3 Redox I
    The whole paper ↗
    June 2024 AS Paper 1, question 9(b)(i): State a reason why this is not a disproportionation reaction. (1)

  8. Q9(b)(ii)

    June 2024 · AS Paper 1

    1 mark3 Redox I
    The whole paper ↗
    June 2024 AS Paper 1, question 9(b)(ii): Identify the reducing agent in this reaction. (1)

  9. Q9(b)(iii)

    June 2024 · AS Paper 1

    1 mark3 Redox I
    The whole paper ↗
    June 2024 AS Paper 1, question 9(b)(iii): Which is the half‑equation for the chlorate(I) ion, ClO– , in this reaction? (1) A ClO– + Cl– → Cl2 + ½O2 + 2e– B ClO– + H+ + e– → ½Cl2 + OH– C ClO– + 2H+ + e–

  10. Q2(c)(iii)

    June 2023 · Paper 3

    2 marks3 Redox I
    The whole paper ↗
    June 2023 Paper 3, question 2(c)(iii): Show, by reference to oxidation number changes, that the decomposition of sodium nitrate is a redox reaction. (2)

  11. Q3(a)(i)

    June 2023 · AS Paper 1

    1 mark3 Redox I
    The whole paper ↗
    June 2023 AS Paper 1, question 3(a)(i): What happens to the atoms of a metal and the Group 7 element when they react together? (1) Metal Group 7 element A gains electrons to form a positive ion loses

  12. Q3(a)(iv)

    June 2023 · AS Paper 1

    1 mark3 Redox I
    The whole paper ↗
    June 2023 AS Paper 1, question 3(a)(iv): Platinum metal reacts with fluorine to give a compound of platinum with an oxidation number of +6. Give the formula of this compound of platinum. (1)

  13. Q4(c)

    June 2023 · AS Paper 1

    1 mark3 Redox I
    The whole paper ↗
    June 2023 AS Paper 1, question 4(c): Bottles of potassium manganate(VII), KMnO4 , have three hazard warning labels. One of these is shown. This hazard symbol means that potassium manganate(VII) is

  14. Q6(a)(i)

    June 2023 · AS Paper 1

    1 mark3 Redox I
    The whole paper ↗
    June 2023 AS Paper 1, question 6(a)(i): State, in terms of electron transfer, what you understand by the terms oxidation and reduction. (1)

  15. Q6(a)(ii)

    June 2023 · AS Paper 1

    2 marks3 Redox I
    The whole paper ↗
    June 2023 AS Paper 1, question 6(a)(ii): Explain, in terms of electron transfer, which of the species is the oxidising agent and which is the reducing agent. (2)

  16. Q6(b)

    June 2023 · AS Paper 1

    4 marks3 Redox I
    The whole paper ↗
    June 2023 AS Paper 1, question 6(b): Bromine reacts with sodium hydroxide solution in a disproportionation reaction –. to form BrO3 Complete the equation for this disproportionation. Justify the ba

  17. Q2(c)

    June 2022 · Paper 1

    2 marks3 Redox I
    The whole paper ↗
    June 2022 Paper 1, question 2(c): Calcium reacts with chlorine. Ca(s) + Cl2(g) → CaCl2(s) Explain, in terms of electrons, why this is a redox reaction. (2)

  18. Q6(c)(ii)

    June 2022 · Paper 2

    1 mark3 Redox I
    The whole paper ↗
    June 2022 Paper 2, question 6(c)(ii): The oxidising agent is acidified Na2Cr2O7 . State the oxidation number of chromium in Na2Cr2O7 . (1)

  19. Q8(c)(i)

    June 2022 · AS Paper 1

    1 mark3 Redox I
    The whole paper ↗
    June 2022 AS Paper 1, question 8(c)(i): Deduce the half‑equation for the formation of chlorine. (1)

  20. Q8(d)(i)

    June 2022 · AS Paper 1

    2 marks3 Redox I
    The whole paper ↗
    June 2022 AS Paper 1, question 8(d)(i): Explain, using oxidation numbers, why this is a disproportionation reaction. (2)
All 45 questions on Redox I, as a list
  1. June 2025, AS Paper 1, Q6(b) (1 mark): Which change in oxidation number of sulfur, if any, occurs during the formation of H2S? (1) A from +6 to −2 B from +6 to +2 C from +2 to −2 D no change
  2. June 2025, AS Paper 1, Q6(c) (2 marks): Deduce the two ionic half-equations for this reaction. State symbols are not required. (2) Oxidation half-equation Reduction half-equation
  3. June 2024, Paper 2, Q3(b) (3 marks): Hydrogen peroxide decomposes to form water and oxygen. 2H2O2(aq) → 2H2O(l) + O2(g) Explain, using oxidation numbers, why the decomposition of hydrogen peroxide
  4. June 2024, Paper 3, Q4(c)(i) (1 mark): Complete the ionic equation for this redox reaction, using oxidation numbers. State symbols are not required. (1) – + OH– + H2O → Al(OH)4 – + NH3 8Al + NO3
  5. June 2024, AS Paper 1, Q5(f) (1 mark): What is the oxidation number of oxygen in the chlorate(III) ion, ClO2 – ? (1) A −1 B +1 C −2 D +2
  6. June 2024, AS Paper 1, Q9(a) (1 mark): Iodine is reduced by thiosulfate ions. The relevant half‑equations are shown. ½I2 + e– → I– 2– → S4O6 2– + 2e– 2S2O3 Deduce an overall equation for this reactio
  7. June 2024, AS Paper 1, Q9(b)(i) (1 mark): State a reason why this is not a disproportionation reaction. (1)
  8. June 2024, AS Paper 1, Q9(b)(ii) (1 mark): Identify the reducing agent in this reaction. (1)
  9. June 2024, AS Paper 1, Q9(b)(iii) (1 mark): Which is the half‑equation for the chlorate(I) ion, ClO– , in this reaction? (1) A ClO– + Cl– → Cl2 + ½O2 + 2e– B ClO– + H+ + e– → ½Cl2 + OH– C ClO– + 2H+ + e–
  10. June 2023, Paper 3, Q2(c)(iii) (2 marks): Show, by reference to oxidation number changes, that the decomposition of sodium nitrate is a redox reaction. (2)
  11. June 2023, AS Paper 1, Q3(a)(i) (1 mark): What happens to the atoms of a metal and the Group 7 element when they react together? (1) Metal Group 7 element A gains electrons to form a positive ion loses
  12. June 2023, AS Paper 1, Q3(a)(iv) (1 mark): Platinum metal reacts with fluorine to give a compound of platinum with an oxidation number of +6. Give the formula of this compound of platinum. (1)
  13. June 2023, AS Paper 1, Q4(c) (1 mark): Bottles of potassium manganate(VII), KMnO4 , have three hazard warning labels. One of these is shown. This hazard symbol means that potassium manganate(VII) is
  14. June 2023, AS Paper 1, Q6(a)(i) (1 mark): State, in terms of electron transfer, what you understand by the terms oxidation and reduction. (1)
  15. June 2023, AS Paper 1, Q6(a)(ii) (2 marks): Explain, in terms of electron transfer, which of the species is the oxidising agent and which is the reducing agent. (2)
  16. June 2023, AS Paper 1, Q6(b) (4 marks): Bromine reacts with sodium hydroxide solution in a disproportionation reaction –. to form BrO3 Complete the equation for this disproportionation. Justify the ba
  17. June 2022, Paper 1, Q2(c) (2 marks): Calcium reacts with chlorine. Ca(s) + Cl2(g) → CaCl2(s) Explain, in terms of electrons, why this is a redox reaction. (2)
  18. June 2022, Paper 2, Q6(c)(ii) (1 mark): The oxidising agent is acidified Na2Cr2O7 . State the oxidation number of chromium in Na2Cr2O7 . (1)
  19. June 2022, AS Paper 1, Q8(c)(i) (1 mark): Deduce the half‑equation for the formation of chlorine. (1)
  20. June 2022, AS Paper 1, Q8(d)(i) (2 marks): Explain, using oxidation numbers, why this is a disproportionation reaction. (2)
  21. November 2021, Paper 3, Q1(b) (1 mark): Write the formula of potassium chlorate(V). (1)
  22. November 2021, AS Paper 1, Q6(b)(i) (2 marks): At room temperature the reaction that occurs is Cl2 + NaOH → NaClO + NaCl Explain, with reference to oxidation numbers, why this is a disproportionation reactio
  23. November 2021, AS Paper 1, Q6(c)(i) (2 marks): Calculate the number of moles of electrons gained by chlorine molecules during this reaction. [Under these conditions one mole of gas occupies 24 dm3] (2)
  24. November 2021, AS Paper 1, Q6(c)(ii) (3 marks): The reducing agent was a solution containing thiosulfate ions, S2O3 The chlorine reacted with 40 cm3 of a 0.20 mol dm–3 solution of these ions. Deduce the numbe
  25. October 2020, Paper 1, Q8(b)(ii) (1 mark): Determine the oxidation number of carbon in the ethanedioate ion, C2O4 (1)
  26. October 2020, Paper 2, Q3(a)(i) (2 marks): Explain, in terms of oxidation numbers, whether or not this is a disproportionation reaction. (2)
  27. June 2019, Paper 3, Q5(a) (1 mark): Name the ion with formula PO3 (1)
  28. June 2019, Paper 3, Q5(b) (1 mark): State what happens to a reducing agent during a reaction, in terms of oxidation number and electrons. (1)
  29. June 2019, Paper 3, Q5(d)(ii) (1 mark): Give a reason why this reaction is not disproportionation. (1)
  30. June 2019, AS Paper 1, Q9(a)(i) (1 mark): This reaction is an example of (1) A oxidation only B reduction only C disproportionation D decomposition
  31. June 2019, AS Paper 1, Q9(b)(i) (1 mark): The following reaction occurs when potassium chlorate(V) is heated at a suitable temperature. Complete the equation by balancing it. State symbols are not requi
  32. June 2018, Paper 1, Q10(a) (1 mark): Write the equation for the reaction of copper with concentrated nitric acid, using the half-equations given in Step 1. State symbols are not required. (1)
  33. June 2018, Paper 2, Q4(b) (3 marks): The second reaction in the airbag is between the sodium produced in the reaction (a)(i) and potassium nitrate. Na + KNO3 → K2O + Na2O + N2 Balance the above equ
  34. June 2018, Paper 2, Q5(a) (2 marks): Balance the ionic half-equation for the reduction of the dichromate(VI) ion. Give the colours of all of the species involved, or state colourless if appropriate
  35. June 2018, AS Paper 1, Q6(b)(i) (2 marks): Complete the table by identifying the oxidation numbers of sulfur in the three sulfur-containing ions. (2) Ion Oxidation number of sulfur 2− S2O3 SO4 2− 2− S4O6
  36. June 2018, AS Paper 1, Q6(b)(ii) (1 mark): The equation for the reaction of iodine with thiosulfate ions is 2− + I2 → 2I− + S4O6 2− 2S2O3 State, in terms of electrons, why iodine is classified as an oxid
  37. June 2018, AS Paper 1, Q6(b)(iii) (1 mark): Use your answer to b(i) to show that chlorine is a stronger oxidising agent than iodine. (1)
  38. June 2018, AS Paper 1, Q6(b)(iv) (2 marks): Chlorine reacts in aqueous solution with S2O3 2− to give SO4 2−. The ionic half-equation for the reaction of chlorine is Cl2 + 2e− → 2Cl− 2− to give SO4 2−. Wri
  39. June 2018, AS Paper 1, Q6(b)(v) (1 mark): Use your answer to (b)(iv) and the half-equation for chlorine, to write the overall ionic equation for the reaction between chlorine and thiosulfate ions. State
  40. June 2017, Paper 1, Q2(a) (3 marks): Explain, in terms of all the relevant oxidation numbers, why this is a redox reaction. (3)
  41. June 2017, AS Paper 1, Q4(a)(i) (1 mark): Write an ionic half-equation for the reduction of chlorine molecules to chloride ions. State symbols are not required. (1)
  42. June 2017, AS Paper 1, Q4(a)(ii) (1 mark): Write an ionic half-equation for the oxidation of chlorine molecules to chlorate(I) ions in the presence of cold, aqueous hydroxide ions. State symbols are not
  43. June 2017, AS Paper 1, Q4(a)(iii) (1 mark): Combine the two equations in (a)(i) and (ii) to give the ionic equation for the reaction of chlorine molecules with cold, aqueous hydroxide ions. (1)
  44. June 2017, AS Paper 1, Q4(a)(iv) (2 marks): Use your answer to (a)(iii) to explain why the reaction is described as a disproportionation reaction. (2)
  45. June 2016, AS Paper 1, Q8(b)(iii) (3 marks): Explain, by using the oxidation numbers of all the atoms, whether or not this is a redox reaction. (3)

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