Preventing rusting by galvanising
2 marks · HardState the two conditions necessary for iron to rust. Explain why covering iron with zinc prevents rusting, even if the zinc layer is scratched.
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Also accept: Oxygen and water required for rusting; zinc is more reactive than iron, so it corrodes first, protecting the iron even if zinc coating is damaged.
Common mistakes: Saying only barrier effect of zinc, not mentioning reactivity or sacrificial protection
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Marking points
B1 · 1 mark · States both oxygen and water needed for rusting.
B2 · 1 mark · Explains zinc protects by being more reactive (sacrificial protection) so iron does not rust even when zinc is scratched.
Worked solution
The two conditions needed for iron to rust are the presence of both oxygen and water.
Covering iron with zinc prevents rusting because zinc is more reactive than iron and will be oxidised (corrode) in preference to the iron, protecting it even if the zinc is scratched.