Redox chemistry: Edexcel International A Level Chemistry questions

Every Edexcel International A Level Chemistry exam question on 8A Redox chemistry (specification points 8.1–8.10), 2019–2025, with its mark scheme and examiner’s report.

All 91 questions on Redox chemistry, as a list

June 2025, AS Unit 2, Q5 (1 mark): Which is the correct order of increasing oxidation number of nitrogen in – and NH3 ? NO , NO3 A NH3 NO NO3 – B NH3 NO3 – NO C NO NH3 NO3 – D NO3 – NH3 NO
June 2025, AS Unit 2, Q6 (1 mark): The most common sources of iodine contain the iodate ion IO3 – . Iodate ions react with iodide ions in acidic conditions as shown. 5I– + IO3 – + 6H+ → 3I2 + 3H2
June 2025, AS Unit 2, Q15(b) (2 marks): Chlorine is used to treat drinking water. Cl2(g) + H2O(l)  HClO(aq) + HCl(aq) By considering oxidation numbers, show that this equation represents a disproport
June 2025, AS Unit 2, Q15(c)(i) (1 mark): The equation for the reaction of concentrated sulfuric acid with potassium chloride is shown. H2SO4 + KCl → HCl + KHSO4 State why this is not a redox reaction.
June 2025, AS Unit 2, Q15(c)(ii) (1 mark): The half-equation for the oxidation of iodide ions is shown. 2I– → I2 + 2e– The half-equation for the reduction of concentrated sulfuric acid to hydrogen sulfid
June 2025, AS Unit 3, Q4(a) (2 marks): Chlorine is generated by the vigorous redox reaction between concentrated hydrochloric acid and potassium manganate(VII). The chlorine moves through the apparat
June 2025 (A), Unit 5, Q3(a) (1 mark): What is the change in oxidation number of a carbon atom when this reaction occurs? (1) A –1 B +1 C +3 D +4
June 2025 (A), Unit 5, Q16(d)(i) (1 mark): Suggest the half‑equation for the reduction of NO2 – to NO under acidic conditions. State symbols are not required. (1)
June 2025 (A), Unit 5, Q16(d)(ii) (1 mark): Derive the equation for the reduction of nitrate(III) ions by iodide ions, using your answer to (d)(i). State symbols are not required. (1)
January 2025, AS Unit 2, Q10 (1 mark): Which equation is not an example of disproportionation? A Cu2O + H2SO4 → Cu + CuSO4 + H2O B 3HNO2 → HNO3 + 2NO + H2O C 3ClO– → 2Cl– + ClO3 – D Mg + 2HCl → MgCl2
January 2025, AS Unit 2, Q17(a)(i) (2 marks): Deduce the oxidation number changes for manganese and carbon. (2) Manganese from to Carbon from to
January 2025, AS Unit 2, Q17(a)(ii) (1 mark): Write the ionic half-equation for the reduction. (1)
January 2025, AS Unit 2, Q17(a)(iii) (1 mark): Write the ionic half-equation for the oxidation. (1)
January 2025, AS Unit 2, Q17(c) (2 marks): Another student suggested that the reaction between manganate(VII) and rhubarb juice could be used to find the concentration of ethanedioic acid in rhubarb juic
October 2024, AS Unit 2, Q19(b)(i) (3 marks): Explain why this is a disproportionation reaction by referring to relevant oxidation numbers. (3)
October 2024, AS Unit 2, Q20(c)(i) (1 mark): Give the overall equation when the cell is being used. State symbols are not required. (1)
October 2024, AS Unit 2, Q20(c)(ii) (2 marks): Describe, with reference to oxidation numbers, what happens to Co when the cell is in use. (2)
October 2024, AS Unit 2, Q20(c)(iii) (1 mark): Suggest one property the separator must have to ensure the lithium battery is viable. (1)
June 2024, AS Unit 1, Q15(b)(i) (2 marks): State two observations that are made when copper metal is added to silver nitrate solution. (2)
June 2024, AS Unit 1, Q15(b)(ii) (2 marks): Write an equation for this displacement reaction. Include state symbols. (2)
June 2024, AS Unit 2, Q18(b)(i) (1 mark): State the meaning of the Roman numerals in chlorate(V) and chlorate(VII). (1)
June 2024, AS Unit 2, Q18(b)(ii) (1 mark): State the oxidation number of chlorine in chlorine dioxide. (1)
June 2024, AS Unit 2, Q18(b)(iii) (2 marks): In Step 2, compound A undergoes disproportionation. Deduce the possible range of oxidation numbers for the chlorine in compound A. Justify your answer. (2)
June 2024, AS Unit 2, Q18(b)(v) (2 marks): Write an equation for each of the two steps in the formation of chlorine dioxide, using your answers in (b). State symbols are not required. (2)
June 2024 (R), AS Unit 2, Q14 (1 mark): Which species contains an element with an oxidation number of +4? A CrO4 2– B MnO4 2– C H2SO4 D Na2CO3
June 2024 (R), AS Unit 2, Q19(b) (3 marks): Ozone can be used in the treatment of drinking water. As well as killing bacteria and viruses, ozone also removes other dissolved impurities such as hydrogen su
January 2024, AS Unit 2, Q6 (1 mark): Which compound does not contain an element with an oxidation number of –1? A HF B NaH C H2O2 D CH4
January 2024, AS Unit 2, Q7 (1 mark): Which reaction involves the oxidation of a Group 7 element? A Br2 + F2 → 2BrF B U + 3ClF3 → UF6 + 3ClF C 2F2 + 2H2O → 4HF + O2 D KCl + H2SO4 → HCl + KHSO4 Use t
January 2024, AS Unit 2, Q21(b)(i) (2 marks): Explain, in terms of oxidation numbers, why this is a redox reaction. (2)
January 2024, AS Unit 3, Q3(c)(i) (2 marks): Write half‑equations for each of these changes. State symbols are not required. (2) Oxidation of iodide ions: Reduction of hydrogen peroxide under acidic condit
January 2024, AS Unit 3, Q3(c)(ii) (1 mark): Write the overall equation for the reaction between iodide ions and hydrogen peroxide solution under acidic conditions. State symbols are not required. (1)
October 2023, AS Unit 2, Q6 (1 mark): What is the value of n in the half‑equation shown? O2(g) + 2H2O(l) + ne– → nOH–(aq) A 2 B 3 C 4 D 5
October 2023, AS Unit 2, Q7 (1 mark): Which equation shows a disproportionation reaction? A Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2 B I2 + 5O3 + H2O → 2HIO3 + 5O2 C 2MnO4 – + MnO2 + 4OH– → 3MnO4 2– + 2H
October 2023, AS Unit 2, Q19(b) (2 marks): Chlorine gas may be prepared by heating concentrated hydrochloric acid with solid manganese(IV) oxide. MnO2(s) + 4HCl(aq) → MnCl2(aq) + Cl2(g) + 2H2O(l) Show, b
October 2023, Unit 5, Q2 (1 mark): In which of these pairs does the transition metal have the same oxidation number? A CrO2Cl2 and [Cr(NH3)4Cl2]+ B [Cu(NH3)2]+ and [CuCl4]2− C Mn2O3 and MnO2 D VO
June 2023, AS Unit 2, Q8 (1 mark): In which pair of compounds is the stated element in the same oxidation state? A chlorine in Cl2O7 and Ca(ClO3)2 B chromium in K2Cr2O7 and K2CrO4 C manganese in
June 2023, AS Unit 2, Q9 (1 mark): What is the formula of barium(II) ferrate(VI)? A Ba2FeO3 B BaFeO3 C Ba2FeO4 D BaFeO4
June 2023, AS Unit 2, Q22(c)(i) (3 marks): State the classification of this reaction. Justify your answer in terms of the relevant oxidation numbers. (3)
June 2023, Unit 5, Q21(b)(i) (2 marks): Explain, using oxidation numbers, why this is a redox reaction. (2)
June 2023, Unit 5, Q21(b)(ii) (2 marks): Deduce the ionic half-equations for this reaction. State symbols are not required. (2)
June 2023, Unit 5, Q21(b)(iii) (1 mark): Complete the equation for this reaction by adding the stoichiometric coefficients. (1) Hg(l) + HNO3(aq) → Hg(NO3)2(aq) + NO(g) + H2O(l)
January 2023, AS Unit 2, Q7 (1 mark): Which ion contains vanadium with an oxidation number of +4? A VO2+ B VO2 + C VO3 – D VO4 3–
January 2023, AS Unit 2, Q8 (1 mark): What is the formula of potassium manganate(VI)? A KMnO4 B K2MnO4 C K3MnO4 D K6Mn2O6 Use this space for any rough working. Anything you write in this space will
January 2023, AS Unit 2, Q18(a) (3 marks): State the type of reaction occurring in the production of Ca(ClO)2 . Justify your answer using oxidation numbers. (3)
January 2023, Unit 5, Q20(b)(i) (2 marks): Chlorine can be prepared in a laboratory by reacting manganese(IV) oxide with concentrated hydrochloric acid. MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O Explain, in terms
October 2022, AS Unit 1, Q1 (1 mark): Which mixture results in a displacement reaction? A iron and copper(II) sulfate solution B lead(II) nitrate solution and sodium iodide solution C dilute hydroch
October 2022, AS Unit 2, Q13 (1 mark): − ? 13 What is the oxidation number of bromine in BrO3 A +1 B +3 C +5 D +7
October 2022, AS Unit 2, Q14 (1 mark): Which reaction is not a disproportionation? A 3Cl2(g) + 6NaOH(aq) → NaClO3(aq) + 5NaCl(aq) + 3H2O(l) B 2H2O2(l) → 2H2O(l) + O2(g) C Cl2(g) + H2O(l) → HCl(aq) +
October 2022, AS Unit 2, Q23(a)(ii) (2 marks): Explain why Step 2 is a redox reaction. Refer to relevant oxidation numbers in your answer. (2)
October 2022, Unit 5, Q1 (1 mark): When copper is added to concentrated nitric acid, a brown gas is given off and the final solution is blue. In terms of oxidation number and electron transfer, h
June 2022, AS Unit 2, Q2 (1 mark): How does an oxidising agent change during a redox reaction? Electrons Oxidation number A gains electrons decreases B gains electrons increases C loses electrons
June 2022, AS Unit 2, Q4 (1 mark): What is the name of the compound with the formula KClO2 ? A potassium chlorate(II) B potassium chlorate(III) C potassium chlorate(IV) D potassium chlorate(V)
June 2022, AS Unit 2, Q5(b) (1 mark): Which element is oxidised and which is reduced when calcium reacts with water? (1) Element oxidised Element reduced A calcium hydrogen B calcium oxygen C hydrog
June 2022, AS Unit 2, Q16(b) (2 marks): Iodate(V) ions, IO3 − , react with iodide ions in acid solution. IO3 − + 5I− + 6H+ → 3I2 + 3H2O Explain, in terms of the oxidation numbers of iodine in the thre
June 2022, Unit 6, Q3(a)(ii) (2 marks): State what would be seen during the reaction. (2)
January 2022, AS Unit 2, Q11 (1 mark): 2− ? 11 Which name is correct for the ion SO4 A sulfate(II) B sulfate(IV) C sulfate(VI) D sulfate(VIII)
January 2022, AS Unit 2, Q12 (1 mark): In which compound is the oxidation number of nitrogen +5? A Ca(NO3)2 B Mg3N2 C N2O3 D NaNO2
January 2022, AS Unit 2, Q13 (1 mark): In which reaction is the copper species acting as an oxidising agent? A Cu2+ + 2Ag → 2Ag+ + Cu B 2Cu+ + O2– → Cu2O C 3Cu + O2 → Cu2O + CuO D Cu + Hg2+ → Hg + Cu
January 2022, AS Unit 2, Q14 (1 mark): Two half‑equations for a reaction are shown. Cu → Cu2+ + 2e− − + 4H+ + 3e− → NO + 2H2O NO3 What is the overall ionic equation for this reaction? A Cu + NO3 − +
January 2022, Unit 5, Q13(b)(i) (1 mark): Complete the half‑equation. (1) AsH3 → As
October 2021, AS Unit 2, Q10(a) (1 mark): What values of x, y and z are needed to balance the equation? (1) x y z A 5 6 8 B 10 3 4 C 5 3 8 D 10 6 4
October 2021, AS Unit 2, Q10(b) (1 mark): What is the reducing agent in the reaction? (1) A H+ B C2O4 2– C MnO4 – D SO4 2–
October 2021, AS Unit 2, Q11 (1 mark): 3– ? 11 What is the oxidation number of phosphorus in the phosphate ion, PO4 A –3 B +3 C +5 D +7
October 2021, AS Unit 2, Q12 (1 mark): Which reaction is not a redox reaction? A 4KClO3(s) ® 3KClO4(s) + KCl(s) B 2HCl(aq) + Ba(OH)2(aq) ® BaCl2(aq) + 2H2O(l) C Zn(s) + CuSO4(aq) ® ZnSO4(aq) + Cu(s)
October 2021, AS Unit 2, Q21(a)(ii) (2 marks): This is a redox reaction. State which element is oxidised and which is reduced. Justify your answer by giving the initial and final oxidation numbers of any ele
October 2021, Unit 6, Q1(d)(i) (1 mark): Copper and zinc both react with concentrated nitric acid to form the metal nitrates, nitrogen dioxide and water. Write the balanced equation for the reaction of
June 2021, AS Unit 1, Q24(c) (2 marks): Magnesium reacts with aqueous iron(II) sulfate in a displacement reaction. Write the ionic equation for this reaction. Include state symbols. (2)
June 2021, AS Unit 2, Q5 (1 mark): What is the oxidation number of chromium in Na2Cr2O7? A +1 B +2 C +3 D +6
June 2021, AS Unit 2, Q6 (1 mark): In an oxide of nitrogen, the oxidation number of nitrogen is +4. Which is the formula of the oxide? A N2O B N2O3 C N2O4 D N2O5
June 2021, AS Unit 2, Q7 (1 mark): Hydrogen peroxide, H2O2 , breaks down into water and oxygen. In terms of oxidation and reduction, how do hydrogen and oxygen change in this reaction? Hydrogen O
June 2021, Unit 5, Q1 (1 mark): In which of the following pairs does the metal have different oxidation numbers? A CrO4 2− and Cr2O7 2− B CrO4 2− and CrO3Cl− C V2O5 and VO4 3− D VO2 + and VO2+
January 2021, AS Unit 2, Q6(b) (1 mark): One of the reaction products is the gas H2S. What is the change in oxidation number of sulfur as H2S forms? (1) A −8 B −6 C −2 D +6
January 2021, AS Unit 2, Q7 (1 mark): −, oxidise dithionate ions, S2O6 2−, according to the equation 7 Iodate(V) ions, IO3 x IO3 − + y S2O6 2− + 4H2O → z SO4 2− + 8H+ + I2 What are the balancing num
January 2021, AS Unit 2, Q8 (1 mark): Magnesium reacts with hydrochloric acid. Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) Which statement about this reaction is correct? A magnesium atoms act as oxidising
January 2021, AS Unit 2, Q22(b) (3 marks): Explain the type of reaction that takes place in Stage 1 of the Liebig Process, using oxidation numbers. 6Ca(OH)2(aq) + 6Cl2(g) → Ca(ClO3)2(aq) + 5CaCl2(aq) + 6
January 2021, AS Unit 2, Q22(d)(i) (1 mark): Give the systematic name of KClO4 . (1)
January 2021, Unit 6, Q2(d) (1 mark): Give the colour change observed in Step 1. (1)
October 2020, AS Unit 1, Q2(a) (1 mark): Which of these is the best name for this type of reaction? (1) A addition B displacement C neutralisation D substitution
October 2020, AS Unit 1, Q2(b) (1 mark): Which is the ionic half‑equation for a process that takes place during this reaction? (1) A Cu2+ + e– → Cu+ B Cu+ + e– → Cu C Zn → Zn+ + e– D Zn → Zn2+ + 2e–
October 2020, AS Unit 2, Q5(a) (1 mark): What type of reaction occurs? (1) A displacement B disproportionation C elimination D hydrolysis
October 2020, AS Unit 2, Q6 (1 mark): Dichromate(VI) ions may be reduced in acidic solution. 2–(aq) + x H+(aq) + y e– → 2Cr3+(aq) + z H2O(l) Cr2O7 The coefficients in this half‑equation are x y z A
October 2020, AS Unit 2, Q7 (1 mark): In an oxide of potassium, the oxidation number of oxygen is –½. What is the formula of this oxide? A K2O B K2O2 C K2O3 D KO2 Use this space for any rough workin
October 2020, AS Unit 2, Q15(a) (2 marks): Silver ions have anti‑microbial properties and are used in some wound dressings. Silver nitrate can be made by warming a mixture of silver metal and concentrate
October 2020, Unit 5, Q14 (1 mark): Which species contains an element with the same oxidation number as bromine in KBrO3? A N2O5 B KMnO4 C K2FeO4 D Na2SO3
October 2020, Unit 5, Q15 (1 mark): Which is a redox reaction? A Cr2O7 2− + 2C → Cr2O3 + CO3 2− + CO B CrO2Cl2 + 4OH− → CrO4 2− + 2Cl− + 2H2O C Cr2O7 2− + 2HCl → 2CrO3Cl− + H2O D 2CrO4 2− + 2H+ →
January 2020, AS Unit 2, Q18(d)(i) (1 mark): State why Reaction 1 is not a redox reaction. (1)
January 2020, AS Unit 2, Q18(d)(iii) (3 marks): The ammonia produced by the hydrolysis of urea reacts with nitrogen monoxide and oxygen to produce nitrogen gas and water. Reaction 2 4NH3(g) + 4NO(g) + O2(g) 4
June 2019, AS Unit 2, Q6 (1 mark): 2–, is 6 The oxidation number of sulfur in the sulfate ion, SO4 A −2 B +4 C +6 D +8 Use this space for any rough working. Anything you write in this space will
June 2019, AS Unit 2, Q7 (1 mark): Which of these is a disproportionation reaction? A 2NaOH + H2SO4 → Na2SO4 + 2H2O B 6NaOH + 3Br2 → 5NaBr + NaBrO3 + 3H2O C 2NaOH + 2Al + 2H2O → 2NaAlO2 + 3H2 D N
June 2019, AS Unit 2, Q19(a)(i) (2 marks): Write half-equations for the oxidation and reduction reactions that take place. State symbols are not required. (2)
June 2019, AS Unit 2, Q19(a)(ii) (1 mark): Use your answers to (a)(i) to write the overall equation for this redox reaction. State symbols are not required. (1)

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