O-LevelChemistryElectrolysis5070/21 · May/June 2023 · Q86 Marks
This question is about electrolysis.
- (a)The table shows some information about the electrolysis of three different electrolytes using graphite electrodes. Complete Table 8.1 with the names of the products at each electrode. Table 8.1 electrolyte product at anode product at cathode dilute aqueous potassium chloride aqueous copper(II) sulfate molten lead(II) iodide[3]
- (b)The electrolysis of aqueous copper(II) sulfate gives different products when copper electrodes are used instead of graphite electrodes. Describe the observations during the electrolysis with copper electrodes.[2]
- (c)Magnesium is manufactured by the electrolysis of molten magnesium chloride. At the anode, chloride ions react to make chlorine molecules. Construct the ionic half-equation for this electrode reaction.[1]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.
- 8(a) KCl (aq) oxygen at anode and hydrogen at cathode CuSO4(aq) oxygen at anode and copper at cathode PbI2(l) iodine at anode and lead at cathode two or three correct products = 1 mark four or five correct products = 2 marks all six products = 3 marks
- 8(b) Any two from: electrolyte stays blue (1) cathode gets coated with a pink solid (1) anode gets smaller (1)
- 8(c) 2Cl- → Cl2 + 2e / 2Cl- – 2e- → Cl2
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