O-LevelChemistryMetals & Reactivity5070/21 · Oct/Nov 2020 · Q710 Marks

Aluminium is extracted by the electrolysis of molten aluminium oxide.

(a)(i)Explain why aluminium is extracted by electrolysis and not by reduction with carbon.[1]
(a)(ii)The electrolyte is a mixture of aluminium oxide and cryolite. Explain the purpose of the cryolite.[1]
(a)(iii)At the positive electrode (anode) oxide ions are converted to oxygen. Construct the equation for this reaction.[1]
(b)(i)Aluminium can also be produced on a small scale by reacting aluminium oxide with magnesium. Al₂O₃ + 3Mg → 2Al + 3MgO Use this equation to explain why the Al₂O₃ is reduced.[1]
(b)(ii)Calculate the maximum mass of aluminium formed when 25.5g of aluminium oxide reacts with excess magnesium.[2]
(c)Aluminium is a metal. Use your knowledge of the structure of metals to explain why aluminium is malleable.[2]
(d)When aluminium is heated in chlorine, aluminium chloride is formed. The reaction is exothermic. Explain, in terms of bond making and bond breaking, why this reaction is exothermic.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[1] 7(a)(i) aluminium is (very) high in the reactivity series / aluminium ions accept electrons less readily than carbon
[1] 7(a)(ii) to dissolve the aluminium oxide
[1] 7(a)(iii) 2O2- → O2 + 4e-
[1] 7(b)(i) oxygen removed from aluminium oxide / it loses oxygen
[2] 7(b)(ii) mol aluminium oxide = 25.5/102 OR 0.25 mol (1) mass of aluminium = 13.5 g (1)
[2] 7(c) (positive) ions in layers (1) layers (easily) slide over each other (1)
[2] 7(d) bond breaking endothermic and bond making exothermic / heat absorbed to break bonds and heat released on making bonds (1) more heat released than absorbed / more energy released than absorbed (1)

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