Extraction and Uses of Metals
6 marks · NormalAluminium is a metal that is extracted from its ore using electrolysis. Aluminium alloys are used for many applications due to their improved properties compared to pure aluminium.
Explain why aluminium is extracted by electrolysis and not by reduction with carbon.
Aluminium objects are usually made from alloys instead of pure aluminium.
Define the term 'alloy'.
Explain, using ideas about the arrangement of atoms, why alloys are harder than pure metals. You may use a labelled diagram or clear description in your answer.
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(a) Aluminium is more reactive than carbon so cannot be extracted by reduction with carbon. Instead, electrolysis is used to remove oxygen from aluminium oxide. · must show States aluminium is above carbon in the reactivity series/more reactive than carbon, Mentions carbon cannot remove oxygen (cannot reduce aluminium oxide), Electrolysis is required as a result (accept: only way to extract aluminium from its ore)
(b(i)) An alloy is a mixture of a metal with other element(s), usually other metals or carbon. · must show States alloy is a mixture, Mentions other metals and/or carbon (or elements)
(b(ii)) Alloys are harder than pure metals because the different sized atoms disrupt the regular arrangement of atoms in the metal lattice, making it more difficult for the layers to slide over each other. · must show Mentions different sized atoms or ions from different elements, States disruption/distortion of metal lattice/layers arrangement, Explains layers cannot slide easily/are less able to slide (idea of hardness), Labelled diagram (optional but credit if shown): shows regular pure lattice vs. distorted alloy lattice
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Marking points
M1 (a) · 1 mark · States or explains that aluminium is above carbon in the reactivity series, so carbon cannot reduce/displace it. (Accept: more reactive than carbon).
M2 (a) · 1 mark · Explains electrolysis is required (not carbon reduction) to extract aluminium from its ore/aluminium oxide; or explains why carbon cannot remove oxygen from aluminium oxide.
B1 (b(i)) · 1 mark · Defines an alloy as a mixture of a metal with other elements, usually other metals or carbon.
M3 (b(ii)) · 1 mark · States that alloys contain different sized atoms (from different elements) or mentions disruption of the atom arrangement.
M4 (b(ii)) · 1 mark · Explains that the different sized atoms break up the regular lattice/disrupt the arrangement.
A1 (b(ii)) · 1 mark · Explains that this disruption makes it more difficult for layers to slide (or increases hardness). Labelled diagram may be credited here if correct.
Worked solution
a) Aluminium is extracted by electrolysis because it is more reactive than carbon and is found above carbon in the reactivity series. This means carbon cannot displace aluminium from its oxide, as aluminium holds onto oxygen more strongly. Therefore, aluminium oxide cannot be reduced by carbon; instead, aluminium oxide is melted and electrolysed to separate aluminium metal from oxygen.
b) i) An alloy is a mixture of a metal with other elements, often other metals or carbon.
ii) In a pure metal, all atoms are the same size and arranged in regular layers. In an alloy, atoms of different elements have different sizes, which distort the layers. This disruption prevents the layers from sliding easily over each other when force is applied, making alloys harder than pure metals.