What is corrosion?

Corrosion is the process by which metals are slowly broken down by reacting with substances in their environment.

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What is the word equation for the rusting of iron?

iron + oxygen + water ➔ hydrated iron(III) oxide

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Why does iron corrode so much more than aluminium?

When aluminium corrodes it forms a protective layer of aluminium oxide, which prevents further corrosion.


When iron corrodes, the hydrated iron(III) oxide flakes off, then the underlying iron also corrodes. 

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Where does corrosion occur?

On the surface of the material (where it's exposed to air).

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What are the two main methods of preventing rusting?

  1. Barrier methods.
  2. Sacrificial methods. 

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What are three ways a barrier might be applied to prevent rusting?

  1. Greasing.
  2. Painting.
  3. Electroplating.

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What does electroplating do?

Electroplating involves using electrolysis to reduce metal ions onto an iron electrode - this process can be used to coat iron with a layer of another metal that won't corrode.

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Describe a common experiment that proves air and water are needed for iron to rust.

If you put an iron nail in a tube with boiled water + oil, it won't rust (boiling removes oxygen from the water, and oil stops air from entering).


If you put an iron nail in a tube with just air, it won't rust (calcium chloride can be used to absorb any water in the air).


If you put an iron nail in a tube with both water and air, it will rust.

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What is the sacrificial method for preventing rusting?

  1. Add a more reactive metal to the iron.
  2. Water and oxygen react with the sacrificial metal instead of the iron, so the iron doesn't rust.

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What happens when zinc is used to galvanise iron?

The layer of Zinc is protective and acts as a barrier.


If scratched, the zinc surrounding the scratch will act as a sacrificial metal, and react with any oxygen/water.

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