Preventing rusting by galvanising
2 marks · NormalState the two conditions necessary for iron to rust. Describe briefly how galvanising prevents rusting.
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Also accept: Presence of both water and oxygen; galvanising coats iron with zinc, acting as barrier and providing sacrificial protection.
Common mistakes: Giving only one condition; not mentioning both barrier and sacrificial action.
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Marking points
B1 · 1 mark · States both water and oxygen are needed for rusting.
B2 · 1 mark · Describes that galvanising coats iron with zinc, which prevents rusting by being a barrier and/or sacrificial protection.
Worked solution
Iron needs both water and oxygen to rust.
Galvanising prevents rusting by coating iron with zinc. The zinc acts as a barrier to water and oxygen, and also protects iron even if scratched by acting as a more reactive (sacrificial) metal.