10.7 Corrosion and its prevention
5 exam questions worth 9 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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What does iron need in order to rust?
Choose one answer.
Correct Not quite: the answer is Oxygen and water
Mark scheme
C
Model answer
C: rusting needs both oxygen and water.
In the rusting experiment, explain why the water in tube B is boiled and covered with a layer of oil.
Mark scheme
- boiling removes dissolved air / oxygen (1)
- oil stops air dissolving back into the water (1)
Model answer
Boiling removes dissolved oxygen from the water, and the oil layer stops air dissolving back in, so there is no oxygen.
Explain how a block of zinc protects the steel hull of a ship from rusting.
Mark scheme
- zinc is more reactive than iron (1)
- so zinc is oxidised / corrodes instead of the iron (1)
Model answer
Zinc is more reactive than iron, so it is oxidised in preference and corrodes instead of the steel.
Explain why galvanised iron is still protected even if the zinc coating is scratched.
Mark scheme
- zinc is more reactive than iron (1)
- so it still corrodes in preference / sacrificial protection (1)
Model answer
The zinc is more reactive than iron, so even where it is scratched, the zinc is oxidised instead of the iron.
In electroplating a spoon with silver, state which electrode the spoon is and what the electrolyte must contain.
Mark scheme
- the spoon is the cathode (1)
- electrolyte contains silver ions (1)
Model answer
The spoon is the cathode, and the electrolyte contains silver ions.
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