Rusting of Iron (Cambridge (CIE) IGCSE Chemistry)
Revision Note
Written by: Caroline Carroll
Reviewed by: Stewart Hird
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Rusting of iron
What is rusting?
Rust is a chemical reaction between iron, water and oxygen to form the compound hydrated iron(III) oxide (rust)
Oxygen and water must be present for rust to occur
During rusting, iron is oxidised
iron + water + oxygen → hydrated iron(III) oxide
Investigating rusting
To investigate the conditions required for rusting, prepare three test tubes as shown in the diagram
The oil in the 2nd tube keeps out air and the water has been boiled so that no air is left in it
The calcium chloride in the 3rd tube is used to remove any moisture in the air
After a few days, the iron nail in the 1st tube will be the only nail to show signs of rust
Requirements for rusting
Diagram showing the requirements of oxygen and water for rust to occur: only the nail on the left rusts
Rust prevention methods
Rust can be prevented by coating iron with barriers that prevent the iron from coming into contact with water and oxygen
However, if the coatings are washed away or scratched, the iron is once again exposed to water and oxygen and will rust
Table to show common barrier methods
Common barrier methods | |
|---|---|
Grease | Oil |
Paint | Plastic |
Examiner Tips and Tricks
Only iron or steel (an alloy made from iron) can rust. If any other metal oxidises in air causing the metal to break down, you should say that the metal has corroded.
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