Specification Point 2.18:
Know the conditions in which Iron rusts

Conditions for Iron to Rust

Rust: A chemical reaction between Iron, Water and Oxygen to form Iron (III) Oxide. The corrosion of iron.

  • Conditions: Oxygen and Water must be present for rust to occur
  • Presence of sodium chloride increases speed of rusting

Iron    +    Water    +    Oxygen    →    Hydrated Iron (III) Oxide

4Fe (s) + 3O2 (g) + 2xH2O (l) → 2Fe2O3xH2O (s)

Conditions for rust, Edexcel IGCSE Chemistry

The requirements of Oxygen and Water for rust to occur

Specification Point 2.19:
Understand how the Rusting of Iron may be prevented by: Barrier Methods, Galvanising, Sacrificial protection

Prevention of Rust

  1. Barrier 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 Prevention of rust, Edexcel IGCSE Chemistry
  1. Galvanising / Sacrificial Protection:
  • Iron can be prevented from rusting using the reactivity series.
  • Galvanising is when the iron is coated with a layer of zinc. ZnCO3 is formed when zinc reacts with oxygen in the air. This protects the iron by barrier method.
  • If the coating is damaged or scratched, the iron is still protected from rusting by the sacrificial method (magnesium can also be used).
  • This is because zinc is more reactive than iron so it reacts with oxygen and water and corrodes instead of the iron.

Example: Sacrificial Anode

Sacrificial Anode, Edexcel IGCSE Chemistry

Zinc Blocks Attached to the Hull of Ships so they will Corrode instead of the Hull

Need help?

Aiming for a Level 9?

See if you’ve got what it takes. Test yourself with our topic questions.

Author: Jamie

Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.