Preventing rusting by galvanising
3 marks · EasyAn iron bridge over a river is being considered for galvanising to prevent rusting.
Describe the process of galvanising.
State how galvanising protects the iron bridge from rusting.
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(a) Iron is coated with a layer of zinc.
(b) The zinc acts as a barrier to water and air and is more reactive than iron, providing sacrificial protection if scratched.
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Marking points
B1 (a) · 1 mark · Describes galvanising as coating iron with a layer of zinc.
B2 (b) · 1 mark · States zinc acts as a barrier to water and air.
B3 (b) · 1 mark · States (or implies) zinc is more reactive than iron and gives sacrificial protection if scratched.
Worked solution
a) Galvanising means the iron is coated with a layer of zinc.
b) The zinc coating prevents air and water from reaching the iron, which stops rusting. If the zinc is scratched, it continues protecting the iron by corroding in place of the iron (sacrificial protection), since zinc is more reactive.