Cambridge O Level Chemistry · Syllabus 5070 · Metals
Galvanising
What is Galvanising?
Coating iron or steel with a layer of zinc. The zinc acts as a barrier that keeps oxygen and water away from the iron, and because zinc is more reactive than iron it also acts sacrificially, so the iron is still protected at any point where the coating is scratched.
This definition is part of the Metals chapter in Cambridge O Level Chemistry.
Questions students ask about Galvanising
Why does galvanising protect iron even after the coating is scratched, but a tin coating does not?
Zinc is more reactive than iron, so at a scratch it loses electrons in preference to the iron and corrodes sacrificially, keeping the iron protected. Tin is less reactive than iron, so it only works as a barrier: once scratched, the exposed iron rusts, and it rusts faster than bare iron because the tin around the scratch draws electrons from it.
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