AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Aluminium has an oxide coating that protects the metal from further…
Full specification wording
Corrosion and its prevention: Aluminium has an oxide coating that protects the metal from further corrosion.
Aluminium reacts quickly with oxygen in air to form a thin, tough layer of aluminium oxide, Al₂O₃, on its surface.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 4 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Aluminium reacts quickly with oxygen in air to form a thin, tough layer of aluminium oxide, Al₂O₃, on its surface. This layer is strongly bonded and unreactive, so it seals the metal underneath from oxygen and water. Unlike rust on iron, which flakes away and exposes fresh metal, the aluminium oxide layer stays intact and stops further corrosion. This is why aluminium resists corrosion despite being more reactive than iron. The coating can be thickened by anodising, which uses electrolysis. If the layer is scratched, it reforms immediately in air.
What earns the marks
- Aluminium reacts with oxygen to form aluminium oxide, Al₂O₃.
- The oxide layer is thin, tough and strongly bonded to the metal.
- The layer acts as a barrier, preventing oxygen and water reaching the metal.
- Unlike rust, the oxide layer does not flake away, so protection continues.
- Aluminium is more reactive than iron yet corrodes less because of this layer.
- Anodising thickens the oxide layer using electrolysis.
Common mistakes and how to put them right
Saying aluminium does not react with oxygen.
Put it right: It reacts readily, forming a protective oxide layer.
Confusing the oxide layer with rust.
Put it right: Rust flakes and exposes iron, while aluminium oxide stays intact.
Thinking aluminium is unreactive because it is low in the reactivity series.
Put it right: It is reactive but protected by its oxide.
Exam tips
- Name the compound as aluminium oxide and give its formula Al₂O₃.
- Contrast the behaviour of the oxide layer with rust on iron.
- Mention that the layer reforms if scratched.
Try the lesson
The start of the Corrosion and its prevention: Aluminium has an oxide coating that protects the metal from further corrosion. lesson, made from checked teaching notes for this specification point.
Have a go first
Which substance forms the protective coating on the surface of aluminium metal?
Listen
Aluminium reacts quickly with oxygen in air to form a thin, tough layer of aluminium oxide, Al₂O₃, on its surface. This layer is strongly bonded and unreactive, so it seals the metal underneath from oxygen and water. Unlike rust on iron, which flakes away and exposes fresh metal, the aluminium oxide layer stays intact and stops further corrosion. This is why aluminium resists corrosion despite being more reactive than iron. The coating can be thickened by anodising, which uses electrolysis. If the layer is scratched, it reforms immediately in air. A strong answer earns marks for these points. Aluminium reacts with oxygen to form aluminium oxide, Al₂O₃. The oxide layer is thin, tough and strongly bonded to the metal. The layer acts as a barrier, preventing oxygen and water reaching the metal. Unlike rust, the oxide layer does not flake away, so protection continues. A common slip: Saying aluminium does not react with oxygen. Instead, it reacts readily, forming a protective oxide layer. Exam tip: Name the compound as aluminium oxide and give its formula Al₂O₃.
Key words
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Oxide layers
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Surface protection
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Corrosion resistance
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Reactivity of metals
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See every definition
- Oxide layers
- Aluminium reacts quickly with oxygen in air to form a thin, tough layer of aluminium oxide, Al₂O₃, on its surface.
- Surface protection
- The strongly bonded, unreactive layer seals the metal underneath from oxygen and water, and if scratched it reforms immediately in air.
- Corrosion resistance
- Aluminium resists corrosion despite being more reactive than iron because the oxide layer stays intact and stops further corrosion.
- Reactivity of metals
- Aluminium is more reactive than iron yet corrodes less because of its protective oxide layer.
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