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Redox and oxidation numbers

Past-paper questions pack

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Questions are numbered; the mark schemes (the answer key) follow on separate pages so the question pages can be handed out alone. www.chemistryaleveltutor.com

OCR AS and A-level Chemistry past-paper questions since 2016 · 78 parts · mark schemes follow the questions · www.chemistryaleveltutor.com · Questions and mark schemes © OCR

1. June 2025 · AS Paper 1 · Q6 · 1 marks ·
6 What is the oxidation number of S in Na2S2O3? A –4 B –2 C +2 D +4 Your answer [1]
2. June 2025 · AS Paper 1 · Q7 · 1 marks ·
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(s) + H2SO4(aq) FeSO4(aq) + H2(g) Your answer [1]
3. June 2025 · Paper 1 · Q15 · 1 marks ·
15 Chromium forms the complex ions [Cr(NH3)6]3+ and [Cr(OH)6]3–. Which statement(s) about the complexes is / are correct? 1 Chromium is in the same oxidation state in each complex ion. 2 The complex ions are different colours. 3 The complex ions have different coordination numbers. A 1, 2 and 3 B Only 1 and 2 C Only 2 and 3 D Only 1 Your answer [1]
4. June 2025 · Paper 1 · Q19(b)(ii) · 3 marks ·
(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 oxidation numbers to show that disproportionation has taken place. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [3]
5. June 2025 · AS Paper 1 · Q22(a) · 3 marks ·
22 This question is about halogens and their compounds. (a) An aqueous solution of bromine reacts with cold aqueous sodium hydroxide in a disproportionation reaction. The equation is shown below. Br2(aq) + 2NaOH(aq) NaBr(aq) + NaBrO(aq) + H2O(l) Explain what is meant by the term disproportionation. Use the equation above and oxidation numbers. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [3]
6. June 2025 · AS Paper 2 · Q2(a)(ii) · 6 marks ·
(ii)* Magnesium and calcium differ in their reactivity. Give a balanced equation for the reaction of calcium with water and describe what would be observed. Explain why this is a redox reaction. Explain the difference in reactivity of magnesium and calcium. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [6] Extra answer space if required. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..........................................................................................................................................................
7. June 2025 · Paper 3 · Q4(a)(i) · 1 marks ·
4 This question is about inorganic chemistry. (a) The flowchart shows reactions involving SO3 2–(aq) ions. (i) What is the systematic name of a SO3 2– ion? ..................................................................................................................................................... [1]
8. June 2025 · Paper 3 · Q4(a)(ii) · 7 marks ·
(ii) Complete the flowchart by adding formulae in the boxes. ................. ................. white precipitate white precipitate Ag+(aq) Ba2+(aq) ................. ................. ................. acidic solution containing three ions Cl 2(aq)/H2O(I) H+(aq)/H2S(g) SO3 2–(aq) ................. ................. yellow solid colourless neutral liquid H+/Cr2O7 2–(aq) Ba2+(aq) green solution white precipitate [7]
9. June 2024 · Paper 1 · Q6 · 1 marks ·
6 Which equation does not represent a disproportionation reaction? A Cl 2 + H2O HCl O + HCl B Cl 2 + 2NaOH NaCl O + NaCl + H2O C 4KCl O3 KCl + 3KCl O4 D 4HCl + MnO2 MnCl 2 + Cl 2 + 2H2O Your answer [1]
10. June 2024 · AS Paper 1 · Q9 · 1 marks ·
9 Which reaction does not show disproportionation of chlorine? A MnO2 + 4HCl MnCl 2 + Cl 2 + 2H2O B Cl 2 + H2O HCl + HCl O C 2Cl O2 + 2NaOH NaCl O2 + NaCl O3 + H2O D 2NaOH + Cl 2 NaCl + NaCl O + H2O Your answer [1]
11. June 2024 · Paper 1 · Q14 · 1 marks ·
14 Chlorine has the electron configuration [Ne]3s23p5. Which statement(s) about chlorine is/are correct when it reacts in redox reactions? 1 It can gain one electron to form 1– ions. 2 It can lose its 3s2 electrons to form 2+ ions. 3 It can lose its 3p5 electrons to form 5+ ions. A 1, 2 and 3 B Only 1 and 2 C Only 2 and 3 D Only 1 Your answer [1]
12. June 2024 · Paper 1 · Q16(b)(iii) · 1 marks ·
(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 of manganese in Mn3O4. ..................................................................................................................................................... [1]
13. June 2024 · AS Paper 1 · Q21(b)(i) · 1 marks ·
(b) Iron can be extracted from iron ores containing the oxide Fe2O3. (i) What is the systematic name for Fe2O3? ..................................................................................................................................................... [1]
14. June 2024 · AS Paper 2 · Q2(b)(i) · 2 marks ·
(b) The reaction between calcium and hydrochloric acid is a redox reaction. Ca(s) + 2HCl (aq) CaCl 2(aq) + H2(g) Equation 2.1 (i) Explain, in terms of electron transfer, why the reaction shown in equation 2.1 is a redox reaction. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [2]
15. June 2024 · Paper 3 · Q4(a)(iii) · 1 marks ·
(iii) The systematic name of H3PO4 is phosphoric(V) acid. What is the systematic name of H3PO3? ..................................................................................................................................................... [1]
16. June 2024 · Paper 3 · Q4(b)(i) · 1 marks ·
(b) Phosphine, PH3, is a poisonous gas. (i) Phosphine reacts with oxygen gas to form phosphorus(V) oxide and water. Write the equation for this reaction. ..................................................................................................................................................... [1]
17. June 2024 · Paper 3 · Q4(b)(ii) · 3 marks ·
(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 a redox reaction. ........ AgNO3 + ........ PH3 + ........ H2O ........ Ag + ........ H3PO3 + ........ HNO3 Explanation ...................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [3]
18. June 2023 · AS Paper 1 · Q5 · 1 marks · AO1
5 Which substance has the lowest oxidation number for sulfur? A Na2SO4 B S8 C SF2 D SO2 Your answer [1]
19. June 2023 · Paper 1 · Q12 · 1 marks · AO2
12 The equations show the electrode potentials of the half-cells used in a lithium-ion cell. E ө / V Li+ + e– Li –3.04 Li+ + CoO2 + e– LiCoO2 +1.16 Which statement is correct in a lithium-ion cell? A The cell potential is 2.88 V. B The reaction at the positive electrode is: LiCoO2 Li+ + CoO2 + e– C The overall cell reaction is: Li + CoO2 LiCoO2 D The oxidation number of Co changes from +2 to +1. Your answer [1]
20. June 2023 · Paper 1 · Q14 · 1 marks · AO1
14 Which statement(s) is/are correct for the anti-cancer complex Pt(NH3)2Cl 2? 1 It has bond angles of 90º. 2 The oxidation number of Pt is +4. 3 It forms both optical and cis-trans isomers. A 1, 2 and 3 B Only 1 and 2 C Only 2 and 3 D Only 1 Your answer [1]
21. June 2023 · Paper 1 · Q15 · 1 marks · AO2
15 Chlorine trifluoride can be decomposed into its elements forming the equilibrium mixture below. 2Cl F3(g) Cl 2(g) + 3F2(g) ∆H = +318 kJ mol–1 colourless green yellow gas gas gas Which statement(s) is/are correct? 1 The decomposition is a redox reaction. 2 When the equilibrium mixture is cooled, the colour fades. 3 The decomposition has a negative entropy change. A 1, 2 and 3 B Only 1 and 2 C Only 2 and 3 D Only 1 Your answer [1]
22. June 2023 · Paper 1 · Q20(d)(i) · 1 marks · AO2
(d) A student reacts an excess of magnesium with 25.0 cm3 of 0.500 mol dm–3 hydrochloric acid, HCl . The student also reacts an excess of magnesium with 25.0 cm3 of 0.500 mol dm–3 ethanoic acid, CH3COOH. (i) Construct an ionic equation for the reaction of magnesium with an acid. ...................................................................................................................................... [1]
23. June 2023 · AS Paper 2 · Q1(b)(i) · 1 marks · AO2
(b) An ore of titanium contains impure TiO2. Titanium is manufactured from TiO2 in a two-stage process. Stage 1 TiO2 + 2C + 2Cl 2 TiCl4 + 2CO Reaction 1.1 Stage 2 TiCl4 + 4Na Ti + 4NaCl Reaction 1.2 (i) The common name for TiO2 is titanium dioxide. What is the systematic name of TiO2? ...................................................................................................................................... [1]
24. June 2023 · AS Paper 2 · Q3(b) · 3 marks · AO1, 2
(b) Chlorine reacts with calcium hydroxide to form Ca(OCl )2, which is the active ingredient in bleaching powder. 2Cl 2 + 2Ca(OH)2 CaCl 2 + Ca(OCl )2 + 2H2O This is a disproportionation reaction. State what is meant by disproportionation and use oxidation numbers to show that disproportionation has taken place. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [3]
25. June 2023 · Paper 3 · Q2(a)(i) · 1 marks · AO1
2 These questions are from different areas of chemistry. (a) This question is about two salts of rubidium (atomic number 37): RbCl O3 and RbCl O4. (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]
26. June 2023 · Paper 3 · Q6(c)(ii) · 3 marks · AO3
(ii) In the reduction process in this reaction, HNO3 and H+ react together to form 2 oxides: X (Mr = 30) and Z (Mr = 18). Determine the formulae of X and Z and write the half-equation for this reduction. X = ...................... Z = ...................... half-equation ................................................................................................................ [3]
27. June 2023 · Paper 3 · Q6(e) · 6 marks · AO3
TURN OVER FOR QUESTION 6 PART (e) (e)* Three reactions involving sulfuric acid are shown below. Reaction 1 Dilute sulfuric acid is reacted with nickel(II) hydroxide to form a green solution. The solvent is allowed to evaporate leaving hydrated crystals of compound D, with the percentage composition by mass: Ni, 22.33%; S, 12.20%; O, 60.87%; H, 4.60%. Reaction 2 Concentrated sulfuric acid is reacted with hydrogen bromide, HBr, to form three products: • an element which exists as diatomic molecules • a gaseous compound E • a liquid. At RTP, 1.00 dm3 of compound E has a mass of 2.67 g. Reaction 3 Concentrated sulfuric acid acts as a catalyst when 2-hydroxypropanoic acid reacts to form compound F (Mr = 144). In this reaction, 2 mol of 2-hydroxypropanoic acid forms 1 mol of compound F and 2 mol of water. Identify compounds D, E and F and construct equations for the reactions. Show structures for any organic compounds. [6] ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... Additional answer space if required. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...................................................................................................................................................
28. June 2022 · Paper 1 · Q6 · 1 marks · AO1
6 Prussian blue, C18Fe7N18, is a deep blue pigment containing Fe2+, Fe3+ and CN− ions. What are the numbers of Fe2+ and Fe3+ ions in one formula unit of C18Fe7N18? A 2 Fe2+ and 5 Fe3+ B 3 Fe2+ and 4 Fe3+ C 4 Fe2+ and 3 Fe3+ D 5 Fe2+ and 2 Fe3+ Your answer [1]
29. June 2022 · Paper 1 · Q21(a)(ii) · 2 marks · AO2
(ii) Write half-equations for the reaction of magnesium with hydrochloric acid. Oxidation half-equation: .................................................................................................... Reduction half-equation: ................................................................................................... [2]
30. June 2022 · Paper 1 · Q22(c) · 6 marks · AO3
TURN OVER FOR QUESTION 22(c) (c)* This question is about copper and copper compounds. Experiment 1 Hydrochloric acid, HCl (aq), is added to an aqueous solution containing [Cu(H2O)6]2+ complex ions. A yellow-green solution forms containing complex ion B. Experiment 2 A piece of copper metal is heated with concentrated sulfuric acid. A reaction takes place forming a pale blue solution C and 45 cm3 of a gas D, measured at RTP. The mass of gas D is 0.12 g. Experiment 3 An excess of copper(II) oxide is heated with dilute nitric acid. The resulting mixture is filtered. The filtrate is a blue solution E. Aqueous potassium iodide, KI(aq), is added to the blue solution E. A white precipitate F and a brown solution G form. Determine the formulae of B–G. Construct equations for the reactions taking place, include any changes in oxidation number, and show your working where appropriate. [6] ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... Additional answer space if required. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...................................................................................................................................................
31. June 2022 · AS Paper 1 · Q23(b) · 2 marks · AO3
(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. Complete the table below for three oxyanions. One row has been completed as an example. Name of oxyanion Ionic charge Formula of oxyanion 1– BrO2 – ...................................... Sulfate(VI) 2– SO4 2– Phosphate(V) 3– ...................................... [2]
32. June 2022 · AS Paper 1 · Q24(a)(ii) · 3 marks · AO2
(ii) Construct the equation for the reaction of chlorine with dilute sodium hydroxide. Use your equation to explain that disproportionation has taken place. Equation ............................................................................................................................ Explanation ....................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... [3]
33. June 2022 · AS Paper 2 · Q2(a)(ii) · 2 marks · AO2
(ii) Using oxidation numbers, explain why the reaction of strontium with water is a redox reaction. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
34. June 2022 · Paper 3 · Q1(a)(ii) · 1 marks · AO1
(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 student disagrees and claims that the nitrogen atoms have different oxidation numbers. Explain with reasons which student is correct. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1]
35. June 2022 · Paper 3 · Q2(a)(ii) · 3 marks · AO1, 2
(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 this decomposition and explain, using oxidation numbers, why this is a disproportionation reaction. equation ............................................................................................................................ explanation ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [3]
36. November 2021 · Paper 1 · Q2 · 1 marks ·
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]
37. November 2021 · Paper 1 · Q19(b)(i) · 2 marks · AO2
(b) In acid conditions, MnO4 2–(aq) disproportionates to form MnO2(s) and MnO4 –(aq). (i) Explain, in terms of oxidation numbers, why disproportionation has taken place. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
38. November 2021 · AS Paper 1 · Q23(b) · 2 marks · AO1
(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 oxidation numbers, show which element has been oxidised and which has been reduced in this reaction. State the changes in oxidation numbers, including all signs. Element oxidised ...................................................... Oxidation number change: from ............. to ............. Element reduced ...................................................... Oxidation number change: from ............. to ............. [2]
39. November 2021 · Paper 3 · Q1(e) · 4 marks · AO2
(e) The structure of lactic acid is shown below. OH OH O lactic acid Complete and balance the equations for two reactions of lactic acid. Reaction with sodium carbonate CH3CH(OH)COOH + .................... ............................................................................................... Reaction with aluminium CH3CH(OH)COOH + .................... ............................................................................................... [4]
40. November 2021 · Paper 3 · Q5(a)(i) · 2 marks · AO1
5 This question is about nitrogen and its compounds. (a) Sodium azide, NaN3, has been used in car airbags. The airbag inflates when the NaN3 decomposes to form nitrogen gas: 2NaN3(s) 2Na(s) + 3N2(g) (i) This is a redox reaction. Write half-equations for the reduction and oxidation processes that take place. Reduction .......................................................................................................................... Oxidation ...................................................................................................................... [2]
41. November 2020 · AS Paper 1 · Q6 · 1 marks · AO1
6 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 oxidised and O is reduced. C O is both oxidised and reduced. D O is oxidised and Cl is reduced. Your answer [1]
42. November 2020 · AS Paper 1 · Q7 · 1 marks · AO1
7 Potassium ferrate(VI) contains two potassium ions for every ferrate(VI) ion. What is the formula of the ferrate(VI) ion? A FeO3 2− B FeO4 2− C FeO5 2− D FeO6 2− Your answer [1]
43. November 2020 · Paper 1 · Q12 · 1 marks · AO2
12 Iodide ions, I−(aq), react with MnO4 −(aq). The unbalanced equation is shown below. I−(aq) + MnO4 −(aq) + H2O(l) IO−(aq) + MnO2(s) + OH−(aq) What is the ratio of MnO2(s) to OH−(aq) in the balanced equation? A 1 : 3 B 1 : 2 C 1 : 1 D 3 : 2 Your answer [1]
44. November 2020 · Paper 1 · Q18(a) · 3 marks · AO1, 2
18 This question is about reactions and uses of the weak acids methanoic acid, HCOOH, and ethanoic acid, CH3COOH. (a) 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 explain, in terms of oxidation numbers, which element has been oxidised and which element has been reduced. Equation ................................................................................................................................... Oxidation .................................................................................................................................. ................................................................................................................................................... Reduction ................................................................................................................................. ................................................................................................................................................... [3]
45. November 2020 · Paper 1 · Q22(b)(ii) · 1 marks · AO2
(ii) Determine the oxidation number of nickel in compound J. oxidation number: ......................................................... [1]
46. November 2020 · AS Paper 2 · Q1(a) · 1 marks · AO2
1 This question is about nickel and its compounds. (a) 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, whether nickel is oxidised or reduced. ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [1]
47. November 2020 · AS Paper 2 · Q3(d)(i) · 1 marks · AO2
(d) Bromine reacts with concentrated sodium hydroxide at 50 °C as in the equation below. 3Br2 + 6NaOH 5NaBr + NaBrO3 + 3H2O (i) Write the systematic name for NaBrO3. ...................................................................................................................................... [1]
48. November 2020 · AS Paper 2 · Q3(d)(ii) · 3 marks · AO1, 2
(ii) This reaction is an example of disproportionation. Use oxidation numbers to explain why. Include the meaning of the term disproportionation. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [3]
49. November 2020 · Paper 3 · Q4(a)(i) · 3 marks · AO2
4 A student carries out an investigation to identify two metals, M and X, by two different methods. (a) The student is provided with a sample of metal M. The student analyses metal M using a ‘back-titration’ technique: • The metal is reacted with excess acid. • The resulting solution is titrated to determine the amount of acid remaining after the reaction. Stage 1 The student adds 100 cm3 of 2.10 mol dm−3 HCl (aq) to 6.90 g of M. An excess of HCl (aq) has been used to ensure that all of metal M reacts. A redox reaction occurs, forming a solution containing M in the +2 oxidation state. Stage 2 The resulting solution from Stage 1 is made up to 250.0 cm3 with distilled water. Stage 3 A 25.00 cm3 sample of the diluted solution from Stage 2 is titrated with 0.320 mol dm−3 NaOH(aq). The NaOH(aq) reacts with excess HCl (aq) that remains in Stage 1: NaOH(aq) + HCl (aq) → NaCl (aq) + H2O(l) The student repeats the titration to obtain concordant titres. Titration results (The trial titre has been omitted.) The burette readings have been recorded to the nearest 0.05 cm3. 1 2 3 Final reading / cm3 27.80 37.55 32.20 Initial reading / cm3 0.50 10.00 5.00 (i) 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 equation, with state symbols, for this reaction. Write half-equations for the oxidation and reduction processes. Overall equation ................................................................................................................ Oxidation half-equation ..................................................................................................... Reduction half-equation .................................................................................................... [3]
50. November 2020 · Paper 3 · Q4(a)(ii) · 2 marks · AO3
(ii) In Stage 1, suggest two observations that would confirm that all of metal M has reacted. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2]
51. June 2019 · Paper 1 · Q2 · 1 marks · AO1
2 Which statement about the reactions of halogens with halide ions is correct? A I2(aq) can oxidise Br−(aq). B Cl 2(aq) can reduce Br−(aq). C Br−(aq) can reduce Cl 2(aq). D Cl −(aq) can oxidise I2(aq). Your answer [1]
52. June 2019 · Paper 1 · Q5 · 1 marks · AO1
5 What is the oxidation number of N in Mg(NO2)2•3H2O? A +2 B +3 C +4 D +5 Your answer [1]
53. June 2019 · Paper 1 · Q6 · 1 marks · AO1
6 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 answer [1]
54. June 2019 · AS Paper 1 · Q8 · 1 marks · AO1
8 A phosphate(V) ion has the formula PO4 3−. What is the formula for copper(I) phosphate(V)? A Cu(PO4)5 B Cu5PO4 C Cu(PO4)3 D Cu3PO4 Your answer [1]
55. June 2019 · AS Paper 1 · Q9 · 1 marks · AO2
9 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 → MnCl2 + Cl2 + 2H2O Your answer [1]
56. June 2019 · AS Paper 2 · Q2(c) · 2 marks · AO2
(c) 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 oxidised and which has been reduced when magnesium nitrate decomposes. State the changes in oxidation numbers, including all signs. Element oxidised ...................................................... Oxidation number change: from ............. to ............. Element reduced ...................................................... Oxidation number change: from ............. to ............. [2]
57. June 2019 · Paper 3 · Q6(a)(ii) · 1 marks · AO3
(ii) 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]
58. June 2018 · Paper 1 · Q2 · 1 marks · AO2
2 In the compound [ICl2]+ [SbCl6]–, the oxidation number of chlorine is –1. What are the oxidation numbers of I and Sb in the compound? I Sb A +1 +5 B +1 +7 C +3 +5 D +3 +7 Your answer [1]
59. June 2018 · AS Paper 1 · Q5 · 1 marks ·
5 Which equation does not represent a neutralisation reaction? A Zn + 2HCl → ZnCl 2 + H2 B 2NH3 + H2SO4 → (NH4)2SO4 C Na2CO3 + 2CH3COOH → 2CH3COONa + CO2 + H2O D CuO + 2HNO3 → Cu(NO3)2 + H2O Your answer [1]
60. June 2018 · AS Paper 1 · Q6 · 1 marks ·
6 What is the oxidation number of Fe in K2FeO4? A +4 B +5 C +6 D +7 Your answer [1]
61. June 2018 · AS Paper 1 · Q7 · 1 marks ·
7 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 + S Your answer [1]
62. June 2018 · AS Paper 1 · Q22(a)(i) · 1 marks ·
22 This question is about compounds of magnesium and phosphorus. (a) A student plans to prepare magnesium phosphate using the redox reaction of magnesium with phosphoric acid, H3PO4. 3Mg(s) + 2H3PO4(aq) → Mg3(PO4)2(s) + 3H2(g) (i) In terms of the number of electrons transferred, explain whether magnesium is being oxidised or reduced. ........................................................................................................................................... ...................................................................................................................................... [1]
63. June 2018 · AS Paper 2 · Q3(b)(i) · 3 marks ·
(b) Iodine can be used for the small-scale purification of drinking water. (i) Iodine reacts with water as shown below. I2 + H2O HI + HIO Using oxidation numbers, explain why this reaction is a disproportionation. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [3]
64. June 2018 · Paper 3 · Q1(a)(vii) · 1 marks ·
(vii) An element which forms a compound with hydrogen in which the element has an oxidation number of –4. .............................. [1]
65. June 2018 · Paper 3 · Q4(a)(i) · 1 marks ·
4 This question is about two compounds used in medicine. (a) Cis-platin, PtCl2(NH3)2, is a complex of platinum which is used in cancer treatment. (i) What is the oxidation number of platinum in cis-platin? ............................ [1]
66. June 2017 · Paper 1 · Q3 · 1 marks ·
3 What is the oxidation number of Mn in K2MnO4? A +4 B +5 C +6 D +7 Your answer [1]
67. June 2017 · Paper 1 · Q17(c)(i) · 3 marks ·
(c) On gently heating, the compound KCl O3 reacts as shown in the equation. 4KCl O3(s) KCl (s) + 3KCl O4(s) This reaction is an example of disproportionation. (i) State what is meant by disproportionation and use oxidation numbers to show that disproportionation has taken place. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [3]
68. June 2017 · Paper 1 · Q17(c)(ii) · 1 marks ·
(ii) What is the systematic name for KCl O4? ...................................................................................................................................... [1]
69. June 2017 · AS Paper 1 · Q24(b)(i) · 1 marks ·
(b) Aluminium is reacted with ethanoic acid. (i) The unbalanced equation for the reaction is shown below. Balance the equation. ……. Al (s) + ……. CH3COOH(aq) → ……. (CH3COO)3Al (aq) + …… H2(g) [1]
70. June 2017 · AS Paper 1 · Q24(b)(ii) · 2 marks ·
(ii) 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 oxidised: .............................. oxidation number change: from .......... to .......... Element reduced: .............................. oxidation number change: from .......... to .......... [2]
71. June 2017 · Paper 3 · Q2(d)(i) · 1 marks ·
(d) Sodium oxide, Na2O, can be prepared by the redox reaction of NaNO2 and sodium metal. Nitrogen gas is also formed. (i) What is the systematic name for NaNO2? ..................................................................................................................................... [1]
72. June 2017 · Paper 3 · Q2(d)(ii) · 2 marks ·
(ii) Using oxidation numbers, with signs, show the element that is oxidised and the element that is reduced in this reaction. Element oxidised .............................. Oxidation number change from ........... to ........... Element reduced .............................. Oxidation number change from ........... to ........... [2]
73. June 2017 · Paper 3 · Q2(d)(iii) · 1 marks ·
(iii) Construct the equation for this reaction. Equation ...................................................................................................................... [1]
74. June 2017 · Paper 3 · Q4(b)(i) · 3 marks ·
(b) The structural formula of compound A is repeated below. O HO OH R compound A Two reactions of compound A are carried out. Suggest an equation for each reaction and state the type of reaction. In your equations, draw structures for organic compounds. You can use R for the alkyl group. (i) Magnesium ribbon is added to a solution of compound A. Gas bubbles are seen and the magnesium slowly dissolves. Equation Type of reaction ........................................................................................................... [3]
75. June 2016 · AS Paper 1 · Q4 · 1 marks ·
3 4 Which equation is not a neutralisation reaction? A Ca(s) + 2HCl(aq) → CaCl2(aq) + H2(g) B H+(aq) + OH–(aq) → H2O(l) C K2CO3(s) + 2HNO3(aq) → 2KNO3(aq) + H2O(l) + CO2(g) D NH3(aq) + HCl(aq) → NH4Cl(aq) Your answer [1]
76. June 2016 · AS Paper 1 · Q5 · 1 marks ·
5 What is the oxidation number of nitrogen in Mg(NO3)2? A –3 B +2 C +5 D +6 Your answer [1]
77. June 2016 · AS Paper 1 · Q22(d) · 2 marks · AO1
(d) 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 sulfuric acid. 2Al(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 3H2(g) Using oxidation numbers, show which element has been oxidised and which has been reduced in this reaction. State the changes in oxidation numbers, including all signs. element oxidised ..................................................................... oxidation number change: from ................ to ......................... element reduced .................................................................... oxidation number change: from ................ to .......................... [2]
78. June 2016 · AS Paper 2 · Q1(a)(ii) · 1 marks · AO1
(ii) Explain what happens when magnesium is oxidised in terms of electron transfer. ........................................................................................................................................... ...................................................................................................................................... [1]

Mark schemes

1. June 2025 · AS Paper 1 · Q6
Mark scheme June 2025 Paper 1 Q6
2. June 2025 · AS Paper 1 · Q7
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3. June 2025 · Paper 1 · Q15
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4. June 2025 · Paper 1 · Q19(b)(ii)
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5. June 2025 · AS Paper 1 · Q22(a)
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6. June 2025 · AS Paper 2 · Q2(a)(ii)
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7. June 2025 · Paper 3 · Q4(a)(i)
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8. June 2025 · Paper 3 · Q4(a)(ii)
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9. June 2024 · Paper 1 · Q6
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10. June 2024 · AS Paper 1 · Q9
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11. June 2024 · Paper 1 · Q14
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12. June 2024 · Paper 1 · Q16(b)(iii)
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13. June 2024 · AS Paper 1 · Q21(b)(i)
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14. June 2024 · AS Paper 2 · Q2(b)(i)
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15. June 2024 · Paper 3 · Q4(a)(iii)
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16. June 2024 · Paper 3 · Q4(b)(i)
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17. June 2024 · Paper 3 · Q4(b)(ii)
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18. June 2023 · AS Paper 1 · Q5
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19. June 2023 · Paper 1 · Q12
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20. June 2023 · Paper 1 · Q14
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21. June 2023 · Paper 1 · Q15
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22. June 2023 · Paper 1 · Q20(d)(i)
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23. June 2023 · AS Paper 2 · Q1(b)(i)
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24. June 2023 · AS Paper 2 · Q3(b)
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25. June 2023 · Paper 3 · Q2(a)(i)
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26. June 2023 · Paper 3 · Q6(c)(ii)
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27. June 2023 · Paper 3 · Q6(e)
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28. June 2022 · Paper 1 · Q6
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29. June 2022 · Paper 1 · Q21(a)(ii)
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30. June 2022 · Paper 1 · Q22(c)
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31. June 2022 · AS Paper 1 · Q23(b)
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32. June 2022 · AS Paper 1 · Q24(a)(ii)
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33. June 2022 · AS Paper 2 · Q2(a)(ii)
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34. June 2022 · Paper 3 · Q1(a)(ii)
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35. June 2022 · Paper 3 · Q2(a)(ii)
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36. November 2021 · Paper 1 · Q2
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37. November 2021 · Paper 1 · Q19(b)(i)
Mark scheme November 2021 Paper 1 Q19(b)(i)
38. November 2021 · AS Paper 1 · Q23(b)
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39. November 2021 · Paper 3 · Q1(e)
Mark scheme November 2021 Paper 3 Q1(e)
40. November 2021 · Paper 3 · Q5(a)(i)
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41. November 2020 · AS Paper 1 · Q6
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42. November 2020 · AS Paper 1 · Q7
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43. November 2020 · Paper 1 · Q12
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44. November 2020 · Paper 1 · Q18(a)
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45. November 2020 · Paper 1 · Q22(b)(ii)
Mark scheme November 2020 Paper 1 Q22(b)(ii)
46. November 2020 · AS Paper 2 · Q1(a)
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47. November 2020 · AS Paper 2 · Q3(d)(i)
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48. November 2020 · AS Paper 2 · Q3(d)(ii)
Mark scheme November 2020 Paper 2 Q3(d)(ii)
49. November 2020 · Paper 3 · Q4(a)(i)
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50. November 2020 · Paper 3 · Q4(a)(ii)
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51. June 2019 · Paper 1 · Q2
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52. June 2019 · Paper 1 · Q5
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53. June 2019 · Paper 1 · Q6
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54. June 2019 · AS Paper 1 · Q8
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55. June 2019 · AS Paper 1 · Q9
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56. June 2019 · AS Paper 2 · Q2(c)
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57. June 2019 · Paper 3 · Q6(a)(ii)
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58. June 2018 · Paper 1 · Q2
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59. June 2018 · AS Paper 1 · Q5
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60. June 2018 · AS Paper 1 · Q6
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61. June 2018 · AS Paper 1 · Q7
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62. June 2018 · AS Paper 1 · Q22(a)(i)
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63. June 2018 · AS Paper 2 · Q3(b)(i)
Mark scheme June 2018 Paper 2 Q3(b)(i)
64. June 2018 · Paper 3 · Q1(a)(vii)
Mark scheme June 2018 Paper 3 Q1(a)(vii)
65. June 2018 · Paper 3 · Q4(a)(i)
Mark scheme June 2018 Paper 3 Q4(a)(i)
66. June 2017 · Paper 1 · Q3
Mark scheme June 2017 Paper 1 Q3
67. June 2017 · Paper 1 · Q17(c)(i)
Mark scheme June 2017 Paper 1 Q17(c)(i)
68. June 2017 · Paper 1 · Q17(c)(ii)
Mark scheme June 2017 Paper 1 Q17(c)(ii)
69. June 2017 · AS Paper 1 · Q24(b)(i)
Mark scheme June 2017 Paper 1 Q24(b)(i)
70. June 2017 · AS Paper 1 · Q24(b)(ii)
Mark scheme June 2017 Paper 1 Q24(b)(ii)
71. June 2017 · Paper 3 · Q2(d)(i)
Mark scheme June 2017 Paper 3 Q2(d)(i)
72. June 2017 · Paper 3 · Q2(d)(ii)
Mark scheme June 2017 Paper 3 Q2(d)(ii)
73. June 2017 · Paper 3 · Q2(d)(iii)
Mark scheme June 2017 Paper 3 Q2(d)(iii)
74. June 2017 · Paper 3 · Q4(b)(i)
Mark scheme June 2017 Paper 3 Q4(b)(i)
75. June 2016 · AS Paper 1 · Q4
Mark scheme June 2016 Paper 1 Q4
76. June 2016 · AS Paper 1 · Q5
Mark scheme June 2016 Paper 1 Q5
77. June 2016 · AS Paper 1 · Q22(d)
Mark scheme June 2016 Paper 1 Q22(d)
78. June 2016 · AS Paper 2 · Q1(a)(ii)
Mark scheme June 2016 Paper 2 Q1(a)(ii)