Preventing rusting by using sacrificial protection
3 marks · EasySome large steel structures are fitted with blocks of magnesium for protection.
State what these magnesium blocks are called.
Describe how these magnesium blocks help prevent the steel structure from rusting.
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(a) Sacrificial anodes
(b) Magnesium is more reactive than iron (in steel), so it is oxidised in preference to the iron, protecting the steel from rusting.
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Marking points
B1 (a) · 1 mark · Correctly names the blocks as sacrificial anodes.
M1 (b) · 1 mark · Explains magnesium is more reactive than iron/steel.
M2 (b) · 1 mark · States magnesium oxidises in place of iron, protecting against rust.
Worked solution
a) They are called sacrificial anodes.
b) Magnesium is more reactive than iron, so it loses electrons and is oxidised instead of the iron. This prevents iron in the steel from rusting.