Uses of metals

O Level / IGCSE Chemistry · Metals. A short explanation of the idea, the rules to remember, the mistake to avoid, a worked example and practice questions with answers.

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The idea

A metal is chosen for a job because its physical properties fit that job. In this topic you match each use to the property that explains it.

Aluminium has a low density, so it is light for its size: useful for aircraft and for overhead cables that hang between pylons. It also conducts electricity well, and it resists corrosion because a thin layer of aluminium oxide covers its surface, which makes it suitable for food containers.

Copper is a very good conductor of electricity and is ductile, so it can be drawn into thin wires that bend without breaking. That is why the wiring in houses is made of copper.

Rules to remember

Common mistake

Giving a property that is true but does not explain the use, such as saying aluminium is used in aircraft because it conducts electricity. Pick the property the job depends on; for overhead cables you need two: low density and good electrical conductivity.

Worked example

A length of overhead cable has a volume of 100 cm3. Compare its mass if it is made of aluminium (density 2.7 g/cm3) or of copper (density 8.9 g/cm3).

  1. mass = density × volume.
  2. Aluminium: 2.7 × 100 = 270 g.
  3. Copper: 8.9 × 100 = 890 g, which is 890 ÷ 270 ≈ 3.3 times as heavy.

Answer: 270 g for aluminium and 890 g for copper, so aluminium cables put a much smaller load on the pylons.

Practice questions

Try each one, then open the answer.

1. Why is aluminium used to make food containers such as trays and cans?

  1. A
    it is magnetic
  2. B
    it resists corrosion
  3. C
    it reacts with acids in food
  4. D
    it has a very high density
Show answer

Answer: B. Aluminium resists corrosion because of its thin oxide layer, so it does not react with food or drinks.

2. Which row correctly matches a metal, its use and the property that explains the use?

  1. A
    aluminium; aircraft bodies; high density, giving strength
  2. B
    aluminium; food containers; high reactivity with acids in food
  3. C
    copper; electrical wiring; good electrical conductivity
  4. D
    copper; electrical wiring; low melting point, so it is easy to shape
Show answer

Answer: C. Copper wiring relies on conductivity and ductility. Aluminium is used in aircraft for its low density and in food containers for its resistance to corrosion.

3. Why would steel be a poor choice for long overhead power cables compared with aluminium?

  1. A
    steel is too ductile, so the cables would stretch and snap
  2. B
    steel has a low melting point, so the cables would melt
  3. C
    steel is magnetic, so it would be attracted towards the pylons
  4. D
    steel has a much higher density, so the cables would be too heavy
Show answer

Answer: D. Steel conducts, but its density is nearly three times that of aluminium. Heavy cables would need many more supports.

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