Preventing rusting by using sacrificial protection
2 marks · EasyA large storage tank for water is made of steel and is buried underground. Magnesium blocks are attached to its surface.
Explain why magnesium is a suitable choice to protect the tank and suggest one other metal that could be used for this purpose.
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Magnesium is more reactive than steel (iron), so it is oxidised first and protects the iron from rusting. Another metal that could be used is zinc or aluminium.
Also accept: Magnesium is more reactive than iron and corrodes instead, protecting the tank. Zinc or aluminium are also suitable sacrificial anodes.
Common mistakes: Any less reactive metal than iron
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Marking points
M1 · 1 mark · Explains that magnesium is more reactive than iron/steel and so is oxidised instead.
B1 · 1 mark · Gives one other suitable metal such as zinc or aluminium.
Worked solution
Magnesium is more reactive than iron (the main metal in steel), so it corrodes and is oxidised instead of the iron. This prevents rusting of the tank. Another suitable metal is zinc or aluminium.