Rusting of Iron (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

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