Preventing rusting by galvanising
4 marks · NormalA farmer is installing a new iron gate that will be exposed to rain and air.
Explain why the gate will rust if left unprotected.
Describe two ways, other than galvanising, that could prevent the gate from rusting.
State and explain why galvanising remains effective even if the zinc coating is scratched.
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(a) Because the iron is exposed to both water (rain) and air (oxygen), which are required for rusting to occur.
(b) Painting or coating with oil/grease (or plastic) to keep water and oxygen away.
(c) Zinc is more reactive than iron; it corrodes instead of iron when scratched (sacrificial protection).
Common mistakes: Only stating one method in (b); Failing to mention sacrificial action in (c)
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States exposure to both water and oxygen causes rusting.
B2 (b) · 1 mark · Names a valid barrier method (painting, oil/grease, plastic, etc.).
B3 (b) · 1 mark · Names a second valid barrier method (different from first).
B4 (c) · 1 mark · Explains that zinc corrodes in place of iron (sacrificial protection) when scratched.
Worked solution
a) The gate will rust because it is exposed to both water (from rain) and oxygen (from the air), which are needed for rusting.
b) The farmer could paint the gate or coat it with oil/grease, or cover it in plastic—these methods keep out water and oxygen.
c) Galvanising still works if scratched because zinc is more reactive than iron and will corrode (oxidise) instead of the iron.