Galvanising & Sacrificial Protection (Cambridge O Level Chemistry)

• Iron can be prevented from rusting using the reactivity series

Sacrificial Protection

• 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
• E.g. using 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