Corrosion of Metals | Chemistry for Grade 11 (IGCSE) PDF Download

Rusting of Iron

• Rusting is a chemical process involving iron, water, and oxygen, resulting in the formation of hydrated iron(III) oxide, commonly known as rust.
• The presence of both oxygen and water is essential for rust formation.
• In the rusting process, iron undergoes oxidation.
  iron water oxygen → hydrated iron(III) oxide

Investigating rusting 

• Prepare three test tubes according to the diagram provided.
• In the second test tube, the presence of oil prevents air from entering, and the water has been boiled to remove any remaining air.
• The third test tube contains calcium chloride, which serves to eliminate moisture from the air.
• After several days, only the iron nail in the first test tube will exhibit signs of rusting.
• Diagram showing the requirements of oxygen and water for rust to occur: only the nail on the left rusts:
  

Rust Prevention Methods

Barrier methods

• Rust formation on iron can be hindered by applying protective coatings that create barriers, thus preventing direct contact with water and oxygen. 
• However, if these coatings are removed or damaged, allowing water and oxygen to reach the iron surface, rusting can occur once more.