Every use of a metal can be traced to a property. Aluminium flies because it is light and does not corrode; copper carries electricity into every home because it conducts well and draws out into wire. Match the property to the use and the marks follow.
Choose a metal by matching its properties to the job. Aluminium is used in aircraft (low density, and strong as an alloy), overhead power cables (low density and a good electrical conductor) and food containers (resistant to corrosion). Copper is used in electrical wiring because it is a good conductor of electricity and is ductile.
Fig. 1: uses of aluminium and copper and the properties behind them
Section 01
Aluminium and copper.
For each use, give the property that makes the metal suitable. Two properties are often needed.
Aluminium in aircraft: low density, so the aircraft is light; its alloys are strong; it resists corrosion.
Aluminium in overhead cables: low density, so the pylons need not support a heavy load; a good conductor of electricity. The cables usually have a steel core for strength.
Aluminium in food containers: resistant to corrosion because of a thin protective oxide layer; non-toxic; malleable, so it can be shaped.
Copper in wiring: an excellent conductor of electricity; ductile, so it can be drawn into wires.
Examiner trap
Aluminium resists corrosion not because it is unreactive (it is high in the reactivity series) but because of a thin, tough layer of aluminium oxide that seals the surface. Say "resists corrosion", not "is unreactive".
Stage 1 · Learn
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Why is aluminium used to make aircraft?
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Why is copper used for electrical wiring?
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Why is aluminium used for food containers?
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Why is aluminium, rather than copper, used for overhead power cables?
Section 02
Choosing a material.
Exam questions often give a table of data and ask you to pick a metal for a job. Look for the property the job needs most.
Metal
Density / g/cm3
Relative conductivity
Resists corrosion?
aluminium
2.7
61
yes (oxide layer)
copper
8.9
100
yes
iron
7.9
17
no, rusts
For overhead cables, aluminium's low density outweighs copper's higher conductivity; for house wiring, weight does not matter, so copper's conductivity wins.
Stage 2 · Exam
Exam-style questions
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Aluminium is a reactive metal, yet aluminium cans do not corrode. Why?
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Using the table in the lesson, which metal would be best for a light, conducting cable that does not rust?
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Which pair of properties must a metal have to be used for electrical wiring?
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Overhead aluminium cables often have a steel core. What does the steel provide?
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