Extraction and Uses of Metals
6 marks · NormalAluminium is a widely used metal found above carbon in the reactivity series.
Explain why aluminium cannot be extracted from its oxide by reacting it with carbon.
State ONE important property of aluminium that makes it suitable for use in overhead electricity cables.
Explain how this property benefits its use in the cables.
Aluminium is usually used as an alloy for practical applications. Give ONE reason why pure aluminium is rarely used.
Explain, in terms of atomic structure, why alloys of aluminium are harder than pure aluminium.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Aluminium is more reactive than carbon, so carbon cannot remove the oxygen from aluminium oxide by reduction. · must show Aluminium more reactive than carbon, Carbon cannot reduce aluminium oxide
(b) Low density OR good electrical conductivity OR resistance to corrosion · must show Property named (any one)
(c) Low density means the cables are lighter OR good conductivity allows electricity to flow easily OR does not corrode easily outdoors · must show Appropriate link to property from (b)
(d) Pure aluminium is not strong / soft / weaker than alloyed aluminium. · must show States lack of strength or softness of pure aluminium
(e) Atoms of different sizes in the alloy disrupt the regular layers, making it harder for layers to slide and thus harder than pure aluminium. · must show Different sized atoms, Disrupted lattice, Reduced layer movement
Common mistakes: Stating that aluminium can be reduced by carbon; Confusing low density with strength for e.g. cables; Claiming pure aluminium is as strong as alloys
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Identifies aluminium is more reactive than carbon.
M2 (a) · 1 mark · States carbon cannot displace oxygen from aluminium oxide.
B1 (b) · 1 mark · Names a correct property: low density, good conductor of electricity, or resists corrosion.
C1 (c) · 1 mark · Links property to benefit for use in cables.
B2 (d) · 1 mark · Gives a correct reason: pure aluminium is soft/not strong.
M3 (e) · 1 mark · Explains alloys are harder due to atoms of different sizes disrupting layers, making sliding difficult.
Worked solution
(a) Aluminium is above carbon in the reactivity series. This means it is more reactive than carbon, so carbon cannot remove (reduce) the oxygen from aluminium oxide to extract aluminium.
(b) One property: Aluminium has a low density / is a good conductor of electricity / resists corrosion.
(c) Low density means that overhead cables are lighter and do not sag as much, or are easier to support. OR: Good conductivity ensures electricity flows efficiently. OR: Corrosion resistance means the cables last longer outdoors.
(d) Pure aluminium is not very strong (it is soft), so is rarely used for structural purposes.
(e) In an alloy, atoms of different sizes distort the layers in the metal structure. This disruption prevents the layers from sliding over each other easily, which makes alloys harder than pure aluminium.