Practise 17 real questions on Electrochemistry from 2021 to 2026. See the answer and explanation as soon as you answer.
Electrochemistry is one of the 18 main topics in our A Level Chemistry (Cambridge (CAIE) 9701) question bank, and about 3% of its real questions come from it. Tayyari Karo has 17 real questions on this topic from 2021 to 2026, from Paper 1, Paper 4; 8 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 14 hard, 3 medium.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
Sulfite ions react separately with zinc and with manganese dioxide: aSO3²⁻(aq) + bH2O(l) + Zn(s) → Zn²⁺(aq) + cOH⁻(aq) + dS2O4²⁻(aq); MnO2(s) + wSO3²⁻(aq) + xH⁺(aq) → Mn²⁺(aq) + yS2O6²⁻(aq) + zH2O(l). Which numbers are correct for a, b, w and x?
Answer: B. a=2, b=2, w=2, x=4
Balancing charge and atoms for both half-reactions gives a=2, b=2, w=2, x=4.
Which equation shows hydrogen acting as an oxidising agent?
Answer: A. H2 + 2K → 2K⁺H⁻
In K⁺H⁻, hydrogen is reduced from 0 to −1 (gains electrons), so H2 is the oxidising agent.
Photochromic glass darkens due to silver atoms. Reaction 1: Ag⁺ + Cl⁻ ⇌ Ag + Cl. Reaction 2: Cu⁺ + Cl → Cu²⁺ + Cl⁻. Reaction 3: Cu²⁺ + Ag → Cu⁺ + Ag⁺. Which statement about these reactions is correct?
Answer: A. Cu⁺ and Cu²⁺ ions act as catalysts.
Cu⁺/Cu²⁺ are regenerated over the cycle (reaction 2 then reaction 3), so overall they act as a catalyst for converting Cl back to Cl⁻, reforming Ag⁺.
Oxygen can be prepared by the reaction of potassium manganate(VII), KMnO4, hydrogen peroxide, H2O2, and sulfuric acid, H2SO4. Each H2O2 molecule loses two electrons in this reaction, and the other products are potassium sulfate, manganese(II) sulfate and water. How many moles of oxygen gas are produced when 1.0 mol of KMnO4 reacts with an excess of H2O2 in acidic conditions?
Answer: B. 2.5 mol
MnO4⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H2O needs 5 mol electrons per mol MnO4⁻; since each H2O2 supplies 2 electrons (H2O2 → O2 + 2H⁺ + 2e⁻), 2.5 mol H2O2 react, producing 2.5 mol O2.
In alkaline solution, MnO4− ions oxidise SO32− ions to SO42− ions. The MnO4− ions are reduced to MnO2. What is the ratio of the two ions (MnO4− : SO32−) in the balanced chemical equation for this reaction?
Answer: A. 2 : 3
Mn goes from +7 to +4 (gain of 3e−); S goes from +4 to +6 (loss of 2e−). Balancing electrons: 2MnO4− (6e− gained) with 3SO32− (6e− lost) gives a 2:3 ratio.
Sodium dichromate(VI), Na2Cr2O7, reacts with hydrogen peroxide, H2O2, producing Cr3+ ions, water and oxygen. What is the correctly balanced ionic equation for this reaction?
Answer: B. Cr2O7²⁻ + 8H+ + 3H2O2 → 2Cr3+ + 7H2O + 3O2
Balancing charge, atoms and electrons for the Cr2O7²⁻/Cr3+ (6e⁻, 14H+ half-equation combined with 3 × H2O2 → O2 + 2H+ + 2e⁻) gives Cr2O7²⁻ + 8H+ + 3H2O2 → 2Cr3+ + 7H2O + 3O2.
| Session | Paper 1 | Paper 4 |
|---|---|---|
| May/June 2026 | – | 1 |
| October/November 2025 | 3 | 1 |
| May/June 2024 | 2 | 1 |
| October/November 2024 | 1 | – |
| October/November 2022 | 1 | 1 |
| May/June 2021 | 1 | 3 |
| October/November 2021 | – | 2 |
17 real A Level Chemistry (9701) questions on Electrochemistry from 2021 to 2026, from Paper 1, Paper 4. Each one shows the year, session and paper it came from.
Yes. Every question shows the correct answer and a short explanation the moment you answer.
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