Preventing rusting by galvanising
4 marks · NormalDescribe two ways to prevent iron from rusting.
Explain why galvanising can still protect iron even if the zinc coating is scratched.
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(a) Painting, coating with oil/grease, or plastic; other valid barrier methods.
(b) Zinc is more reactive than iron and will corrode instead of iron, protecting iron even if the coating is damaged.
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Marking points
B1 (a) · 1 mark · States one correct method of preventing rust (e.g. painting, oiling, plastic coating, barrier).
B2 (a) · 1 mark · States a second correct and different method.
B3 (b) · 1 mark · Explains that zinc is more reactive than iron.
B4 (b) · 1 mark · States that zinc corrodes (oxidises) instead of iron (sacrificial protection).
Worked solution
a) Iron can be protected from rusting by painting the surface or by coating it in oil or grease. Other ways include plastic coating or tin coating.
b) Galvanising works because zinc is more reactive than iron. If the zinc coating is scratched, the zinc still protects the iron by corroding (oxidising) first — this is called sacrificial protection.