Rusting of Iron (Cambridge (CIE) IGCSE Combined Science): Revision Note

Rusting of iron

What is rusting?

• Rusting is a chemical reaction between iron, water and oxygen

  • Rust is the reddish-brown compound product called hydrated iron(III) oxide

• Both oxygen and water must be present for rusting 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:

• Test-tube 1 contains water and air (oxygen)

  • After a few days, the iron nail in this test-tube will show signs of rust

• Test-tube 2 contains water but no air (oxygen)

  • After a few days, this test-tube will not show signs of rust because:

    • The oil layer keeps out air

    • The water has been boiled so that no air is left in it

• Test-tube 3 contains air (oxygen) but no water

  • After a few days, this test-tube will not show signs of rust because:

    • The calcium chloride removes any moisture in the air

Rust prevention methods

• Rust can be prevented using barrier methods

  • A barrier is some form of coating that prevents iron from coming into contact with water and oxygen

• Common barrier methods include:

  • Grease / oil

  • Paint

  • Plastic coating

• However, if the barriers are removed or scratched, the iron is exposed to water and oxygen and will rust