Explain why adding small amounts of other metals to iron to form an alloy can make it more useful for construction purposes than pure iron alone.

Edexcel GCSE Chemistry (1CH0) — 5.1 Transition metals, alloys and corrosion (Chem only) · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Steel is an alloy of iron widely used in the construction of bridges and buildings. Unlike pure iron, steel can be engineered to have a range of different properties depending on which metals are added to it.

Model answer (4 marks)

An alloy is made by combining two or more metals together.
The different‑sized atoms disrupt the regular arrangement of atoms in pure iron.
This makes the alloy harder/stronger than pure iron.
Alloys can also give greater resistance to corrosion compared to pure iron.

Examiner tips

  • Use the word ‘alloy’ and mention ‘combining two or more metals’.
  • Explain the lattice disruption and link it to hardness/strength.
  • Include the corrosion resistance point.
  • Keep each point concise to fit the 4 marks.

Common mistakes

  • Failing to state that an alloy is a mixture of metals.
  • Confusing alloying with alloy composition percentages.
  • Omitting the corrosion resistance benefit.

Mark scheme (4 marks)

  1. An alloy is made by combining two or more metals together
  2. The different-sized atoms disrupt the regular arrangement of atoms in pure iron
  3. This makes the alloy harder/stronger than pure iron
  4. Alloys can also give greater resistance to corrosion compared to pure iron

Key terms in this question

alloy

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