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CAIE A Level Chemistry 9701

Electrochemistry questions

Exam-style questions on Electrochemistry, ordered from foundation to challenge. Pick one, write your answer the way you would in the exam, and it comes back marked against the mark scheme, point by point.

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Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.

  1. Explain4 marksStandardA student electrolyses dilute aqueous sodium chloride using inert carbon electrodes. The products at the electrodes are hydrogen and oxygen. Explain why these products are formed rather than sodium and chlorine.
  2. Explain4 marksStandardA voltaic cell is constructed by connecting a cePb(s) Pb^2+(aq) half-cell to an ceAg(s) Ag^+(aq) half-cell. The standard electrode potentials are: cePb^2+(aq) + 2e- - Pb(s) E^° = -0.13 V ceAg^+(aq) + e- - Ag(s) E^° =…
  3. Suggest4 marksStandardBromine water is added to a colourless aqueous solution of potassium iodide. The mixture turns brown as iodine is formed. Br2(aq) + 2I^-(aq) → 2Br^-(aq) + I2(aq) Suggest which species is the oxidising agent in this…
  4. Compare5 marksStandardChlorine is bubbled into cold dilute aqueous sodium hydroxide, forming sodium chloride and sodium chlorate(I). Reaction 1: Cl2 + 2NaOH → NaCl + NaClO + H2O With hot concentrated aqueous sodium hydroxide, the product is…
  5. Describe5 marksStandardWhen hydrogen gas is passed over heated iron(III) oxide, the following reaction occurs. Fe2O3(s) + 3H2(g) → 2Fe(s) + 3H2O(g) Describe this reaction as a redox reaction. In your answer, refer to oxidation numbers…
  6. Compare5 marksStandardA student electrolyses two samples of copper(II) chloride, CuCl2. One sample is molten, the other is an aqueous solution. Both use inert electrodes. Compare the products formed at the anode and cathode in the two…
  7. Suggest4 marksStandardConcentrated aqueous sodium chloride is electrolysed using inert electrodes. State the substance liberated at the anode and the substance liberated at the cathode, and explain your reasoning in terms of the species…
  8. Explain4 marksStandardA student electrolyses an aqueous solution of copper(II) sulfate using inert carbon electrodes. The concentration of the electrolyte is changed from 0.1 mol dm^-3 to 0.5 mol dm^-3. Explain how the change in…
  9. Suggest4 marksStandardMagnesium ribbon burns in nitrogen gas to form the white solid magnesium nitride, Mg3N2. 3Mg(s) + N2(g) → Mg3N2(s) Suggest, in terms of electron transfer and changes in oxidation number, why this reaction is a redox…
  10. Compare5 marksStandardTwo reactions are shown below. Reaction 1: 2FeCl3(aq) + Zn(s) → 2FeCl2(aq) + ZnCl2(aq) Reaction 2: Cl2(g) + 2NaOH(aq) → NaCl(aq) + NaClO(aq) + H2O(l) Compare the redox changes in these two reactions. In your answer you…
  11. Explain4 marksStandardIn aqueous solution, copper(I) chloride undergoes the following reaction. 2CuCl → Cu + CuCl2 Explain, in terms of changes in oxidation number and electron transfer, why this reaction is a disproportionation reaction…
  12. Explain4 marksStandardTwo electrolytic experiments are described. Experiment 1: An aqueous solution of sodium chloride is electrolysed using inert platinum electrodes. A very dilute solution is used, and then the experiment is repeated…
  13. Compare5 marksStandardCompare the products formed at the electrodes when molten aluminium oxide is electrolysed with the products formed when aqueous aluminium sulfate is electrolysed. In your answer, refer to the ions present and the…
  14. Explain4 marksStandardLead(IV) oxide reacts with concentrated hydrochloric acid. PbO2 + 4HCl → PbCl2 + Cl2 + 2H2O Explain, in terms of changes in oxidation number and electron transfer, why this reaction is a redox reaction. Identify the…
  15. Explain4 marksStandardA student wishes to measure the standard electrode potential of the ceFe^3+/Fe^2+ electrode. The electrode is made by dipping a platinum wire into a solution containing both ceFe^3+ and ceFe^2+ ions. (a) Explain why a…
  16. Compare5 marksStandardCompare the method used to measure the standard electrode potential of a non-metal in contact with its ions, for example chlorine in aqueous potassium chloride, with the method used to measure the standard electrode…
  17. Suggest4 marksStandardConcentrated aqueous sodium chloride is electrolysed using inert electrodes. Suggest the identity of the substances liberated at each electrode, and explain your reasoning in terms of the ions present and their…
  18. Describe5 marksStandardA student determines a value for the Avogadro constant using an electrolytic method. Two silver electrodes are placed in an aqueous solution of silver nitrate, AgNO3. A steady current is passed through the cell for a…
  19. Compare5 marksStandardAcidified potassium dichromate(VI) reacts with sodium sulfite. The ionic equation for the reaction is shown. ceCr2O7^2-(aq) + 3SO3^2-(aq) + 8H+(aq) - 2Cr^3+(aq) + 3SO4^2-(aq) + 4H2O(l) (a) Using Roman numerals to show…
  20. Compare5 marksStandardTwo electrolytic cells are set up using inert electrodes. Cell 1 contains dilute aqueous copper(II) chloride. Cell 2 contains concentrated aqueous copper(II) chloride. Compare the products formed at the anode and…
  21. Describe5 marksStandardMolten lead(II) bromide, PbBr2, is electrolysed using inert graphite electrodes. Describe the observations at each electrode and explain why these products are formed. In your answer, refer to the movement of ions and…
  22. Explain4 marksStandardThe Roman numeral (IV) in the name lead(IV) oxide indicates the oxidation number of lead in PbO2. Lead(IV) oxide reacts with concentrated hydrochloric acid: PbO2 + 4HCl → PbCl2 + Cl2 + 2H2O Explain, using oxidation…
  23. Describe5 marksStandardZinc metal is added to an aqueous solution of iron(III) sulfate. The reaction produces zinc sulfate and iron(II) sulfate. Describe this reaction in terms of electron transfer and changes in oxidation number. Identify…
  24. Explain4 marksStandardConsider the following reaction: 2FeCl3 + SnCl2 → 2FeCl2 + SnCl4 Explain, in terms of electron transfer and changes in oxidation number, the redox process that occurs. Include the oxidation numbers of the elements…
  25. Describe5 marksStandardA student sets up a simple cell using the two half-cells described below. Half-cell 1: a silver electrode in contact with Ag+ ions, Ag+(aq) + e- → Ag(s) Half-cell 2: a copper electrode in contact with Cu^2+ ions…
  26. Explain4 marksStandardA student wants to measure the standard electrode potential of the ceFe^3+/Fe^2+ half-cell. The student sets up a cell with a platinum electrode dipped into a solution containing both ceFe^3+(aq) and ceFe^2+(aq) ions…
  27. Compare5 marksStandardTwo electrolytic cells are set up. Cell 1 contains molten sodium chloride. Cell 2 contains dilute aqueous sodium chloride. Both are electrolysed using inert platinum electrodes. Compare the products formed at the anode…
  28. Compare5 marksStandardCompare the methods used to measure the standard electrode potential of (i) a metal in contact with its aqueous ions, and (ii) an ion of the same element in two different oxidation states. In your comparison, include…
  29. Describe7 marksChallengeConsider the following unbalanced chemical equation. Pb3O4 + HCl → PbCl2 + Cl2 + H2O In Pb3O4, lead exists in two oxidation states: +2 and +4, as indicated by the Roman numerals in the name 'lead(II,IV) oxide'…
  30. Explain6 marksChallengeAn aqueous solution of copper(II) sulfate is electrolysed using copper electrodes. The solution is dilute. State and explain which substance is liberated at the anode.
  31. Describe7 marksChallengeVanadium(V) oxide reacts with calcium at high temperature to form vanadium and calcium oxide. V2O5 + Ca → V + CaO Describe this reaction in terms of electron transfer and changes in oxidation number. State the…
  32. Describe7 marksChallengeA student carries out an electrolysis experiment using a concentrated aqueous solution of sodium chloride. Inert carbon electrodes are used. The student measures the volume of gas collected at the cathode over a…
  33. Describe5 marksChallengeA student writes the following equation for the reaction between zinc and iron(III) sulfate and believes it is balanced. Zn + Fe2(SO4)3 → ZnSO4 + FeSO4 Describe how changes in oxidation number are used to show that…
  34. Suggest5 marksChallengeMagnesium burns in nitrogen to form magnesium nitride, Mg3N2. The unbalanced equation is: Mg(s) + N2(g) → Mg3N2(s) Suggest how oxidation numbers can be used to balance this equation, and identify the oxidising agent…
  35. Describe7 marksChallengeA student determines the Avogadro constant, L, using a silver coulometer. Two clean silver electrodes are placed in an aqueous solution of silver nitrate, AgNO3. A steady current of 0.50\,A is passed for exactly…
  36. Describe7 marksChallengeStandard electrode potentials for three half-reactions are given. ceFe^3+(aq) + e^- <= Fe^2+(aq) E^° = +0.77 V I2(s) + 2e^- ⇌ 2I^-(aq) E^° = +0.54 V ceCe^4+(aq) + e^- <= Ce^3+(aq) E^° = +1.44 V (a) Define the terms…
  37. Describe5 marksChallengeA student electrolyses molten lead(II) bromide, PbBr2, using inert carbon electrodes. During the electrolysis, a dark grey metal forms at the cathode and a red-brown gas is released at the anode. Describe, in terms of…
  38. Suggest5 marksChallengeA student carries out two electrolysis experiments. Experiment 1: A concentrated aqueous solution of NaCl is electrolysed using inert electrodes. Experiment 2: A molten sample of NaCl is electrolysed using inert…
  39. Suggest6 marksChallengeA student electrolyses aqueous sodium chloride using inert carbon electrodes. The electrolyte is a concentrated solution of sodium chloride. The student records the products at each electrode. The student then repeats…
  40. Compare6 marksChallengeAluminium chloride can be electrolysed either as a molten salt or as an aqueous solution. In both cases, graphite electrodes are used. Compare the products formed at the anode and at the cathode in the two cases, and…
  41. Suggest6 marksChallengeChlorine gas is bubbled into cold, dilute sodium hydroxide solution. The reaction produces sodium chloride, sodium chlorate(I) and water. Suggest what this reaction shows about the oxidation numbers of chlorine and…
  42. Compare7 marksChallengeChlorine reacts with cold dilute aqueous sodium hydroxide to form sodium chlorate(I), NaClO, and sodium chloride. (a) State the oxidation number of chlorine in NaClO, and write the Roman numeral that indicates the…
  43. Explain7 marksChallengeHot concentrated aqueous potassium hydroxide reacts with iodine. The unbalanced equation for the reaction is shown. I2 + KOH → KI + KIO3 + H2O Explain, using oxidation numbers, how the equation is balanced. In your…
  44. Compare6 marksChallengeIn acidic solution, sulfite ions, ceSO3^2-, are oxidised to sulfate ions, ceSO4^2-, by dichromate ions, ceCr2O7^2-, which are reduced to chromium(III) ions, ceCr^3+. Compare oxidation and reduction in this reaction in…