Corrosion and its Prevention
Recap Corrosion and its Prevention for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) chemistry topic: rusting needs both air and water, and can be prevented by barriers or by sacrificial protection.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Corrosion is the destruction of materials by chemical reactions with substances in the environment. Rusting is the corrosion of iron. This is a Triple-only topic.
Both air and water are required for iron to rust. If either is absent, rusting does not occur — which is why the standard experiment uses three tubes, one with both, one with water only, and one with dry air only.
Corrosion can be prevented by coating with a barrier such as greasing, painting or electroplating, which excludes air and water. Aluminium has an oxide coating that protects it. Sacrificial protection uses a more reactive metal, such as zinc on galvanised iron, which corrodes in preference to the iron.
Revision notes
What rusting requires
Both air, specifically oxygen, and water are required for iron to rust.
If either is absent, rusting does not occur. The standard experiment demonstrates this with three tubes: one with air and water, one with boiled water and oil to exclude air, and one with dry air and a drying agent.
Barrier methods
Coating iron excludes air and water, preventing rusting.
Methods include greasing, painting and electroplating. Aluminium does not need this because it forms a protective oxide coating that does not flake off.
Sacrificial protection
A more reactive metal is placed in contact with the iron.
Zinc is used to galvanise iron. Because zinc is more reactive, it corrodes in preference to the iron, protecting it even if the coating is scratched — an advantage over paint.
Key points
- Corrosion is destruction by reaction with the environment.
- Rusting is the corrosion of iron.
- Both air and water are needed for rusting.
- Barrier methods exclude air and water.
- Aluminium has a protective oxide coating.
- Sacrificial protection uses a more reactive metal.
Worked examples
Example 1
State the two substances required for iron to rust. [2 marks]
Model answer
Air, specifically oxygen (1 mark), and water (1 mark).
Example 2
Explain how galvanising protects iron from rusting. [3 marks]
Model answer
The iron is coated with zinc, which acts as a barrier excluding air and water (1 mark). Zinc is also more reactive than iron (1 mark), so it corrodes in preference to the iron, protecting it even if the coating is scratched (1 mark).
Example 3
Explain why aluminium does not corrode in the same way as iron. [2 marks]
Model answer
Aluminium forms a protective oxide coating on its surface (1 mark), which does not flake off and so prevents further reaction with air and water (1 mark).
Common mistakes
Saying only water is needed for rusting.
Both air and water are required.
Saying paint gives sacrificial protection.
Paint is a barrier method only. Sacrificial protection requires a more reactive metal.
Forgetting the advantage of sacrificial protection.
It continues to protect even when scratched, unlike a barrier.
Saying aluminium does not react with oxygen.
It does, but the oxide layer formed protects it from further reaction.
Exam tips
- State both air and water as requirements for rusting.
- Explain galvanising as both a barrier and sacrificial protection.
- Give the scratched-coating advantage for sacrificial protection.
- Remember this is a Triple-only topic.
Key terms
- Corrosion
- Destruction of a material by reaction with its environment.
- Rusting
- The corrosion of iron, requiring air and water.
- Galvanising
- Coating iron with zinc for sacrificial protection.
- Sacrificial protection
- Using a more reactive metal that corrodes instead.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.