Galvanising & Sacrificial Protection (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

Extended tier only

Sacrificial Protection

• Iron can be prevented from rusting using the reactivity series
• A more reactive metal can be attached to a less reactive metal
• The more reactive metal will oxidise and therefore corrode first, protecting the less reactive metal from corrosion

Zinc bars on the side of steel ships

Diagram to show the use of zinc bars on the sides of steel ships as a method of sacrificial protection

• Zinc is more reactive than iron therefore will lose its electrons more easily than iron and is oxidised more easily:

Zn → Zn²⁺ + 2e^-

• The iron is less reactive therefore will not lose its electrons as easily so it is not oxidised; the zinc is sacrificed to protect the steel
• For continued protection, the zinc bars have to be replaced before they completely corrode

Galvanising

• Galvanising is a process where the iron to be protected is coated with a layer of zinc
• This can be done by electroplating or dipping it into molten zinc
• ZnCO₃ is formed when zinc reacts with oxygen and carbon dioxide in the air and protects the iron by the barrier method
• If the coating is damaged or scratched, the iron is still protected from rusting by sacrificial protection