O-LevelChemistryElectrolysis5070/22 · May/June 2015 · Q57 Marks
Electrolysis is often used in the extraction and purification of elements.
- (a)Magnesium is manufactured by the electrolysis of molten magnesium chloride. Write equations for the two electrode reactions that occur during this electrolysis.[2]
- (b)(i)Copper can be purified using the electrolysis of aqueous copper(II) sulfate. What is used as the anode (positive electrode)?[1]
- (b)(ii)What is used as the cathode (negative electrode)?[1]
- (c)Chlorine can be made by the electrolysis of concentrated aqueous sodium chloride. The overall process can be represented by the following equation. 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g) 55 dm3 of 3.5mol/dm3 aqueous sodium chloride is electrolysed. What is the maximum volume of chlorine that can be formed, measured at room temperature and pressure?[3]
Mark scheme
Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.
- [2] (a) (i) Mg2+ + 2e- → Mg (1)
- (ii) 2Cl¯ → Cl2 + 2e¯ (1)
- [1] (b) (i) Impure copper (1)
- [1] (ii) Pure copper (1)
- [3] (c) Moles of NaCl = 55 × 3.5 OR 192.5 (1)
- Moles of Cl2 = 96.25/96.3/idea of dividing moles by 2 (1)
- Volume = 2310(dm³) (1)
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