Describe how galvanising protects iron from rusting, and explain why this protection continues even if the zinc coating is scratched to expose the iron beneath.

Cambridge International IGCSE Chemistry (0620) — 9.5 Corrosion of metals · Describe and Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Galvanising is the process of coating iron with a layer of zinc.

The zinc layer acts as a physical barrier, preventing oxygen and water from reaching the iron surface.

Zinc is more reactive than iron (it sits higher in the reactivity series). When the coating is damaged and iron is exposed, the zinc still corrodes preferentially.

Because the zinc corrodes first, it supplies electrons to the iron, protecting it – a sacrificial protection mechanism.

Examiner tips

  • Use the phrase ‘sacrificial protection’ – examiners look for this term.
  • Show the order of reactivity (Zn > Fe) to justify why zinc corrodes first.
  • Mention the barrier effect and the electron transfer to cover both parts of the question.

Common mistakes

  • Confusing the roles of zinc and iron, e.g. saying iron protects zinc.
  • Omitting the reactivity series explanation or the sacrificial protection concept.
  • Using vague terms like ‘protects’ without explaining the mechanism.

Mark scheme (4 marks)

  1. Galvanising involves coating iron with a layer of zinc
  2. The zinc layer acts as a barrier, preventing oxygen and water from reaching the iron surface
  3. Zinc is more reactive than iron / zinc is higher than iron in the reactivity series
  4. Zinc corrodes (oxidises/reacts) in preference to the iron, so the iron remains protected — this is sacrificial protection

Key terms in this question

galvanising

Related

More Corrosion of metals questions

▶ Try answering this question with AI marking (free) →