Preventing rusting by galvanising
2 marks · EasyExplain why galvanising is able to protect iron from rusting even when the zinc coating is scratched.
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Zinc is more reactive than iron. When scratched, zinc continues to protect iron by corroding (sacrificial protection).
Also accept: Zinc corrodes instead of iron; Zinc is oxidised instead of iron
Common mistakes: Only acts as a barrier; Zinc sealing the scratch
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Marking points
B1 · 1 mark · States or implies zinc is more reactive than iron.
B2 · 1 mark · Explains zinc corrodes/oxidises in place of iron, protecting iron from rusting even when coating is scratched (sacrificial protection).
Worked solution
Galvanising protects iron in two ways. First, zinc forms a barrier to air and water. When zinc is scratched, zinc is still more reactive than iron, so the zinc continues to corrode instead of the iron. This is called sacrificial protection and prevents the iron from rusting even if the surface is damaged.