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GCSE Chemistry · key term
Protection in which a more reactive metal corrodes instead of the metal being protected.
Used by AQA, Edexcel and OCR
Specification 4.10.3.1 · Paper 2
Revise: Corrosion and PreventionAn intact zinc coating separates the iron from air and water, but it also provides sacrificial protection. Zinc is more reactive than iron, so zinc corrodes in preference to the iron. This means zinc can continue to protect nearby exposed iron if the coating is scratched, provided the zinc remains in contact with it.
Specification 5.3C · Paper 1
Protection of iron by a more reactive metal that oxidises in preference to the iron.
Revise: Prevention of RustingSacrificial protection uses a metal more reactive than iron, such as zinc or magnesium, in contact with the iron. The more reactive metal has a greater tendency to lose electrons, so it oxidises in preference to the iron. It is gradually used up while protecting the iron.
Specification C6.1q · Paper 2 (Foundation), Paper 4 (Higher)
Protection in which an electrically connected, more reactive metal corrodes instead of the metal being protected.
Revise: Corrosion MitigationTin is less reactive than iron, however, so it does not provide sacrificial protection if the coating is damaged; exposed iron can then corrode.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
Protection in which a more reactive metal is oxidised instead of the metal being protected.
Revise: Corrosion and preventionA second approach is sacrificial protection. A more reactive metal, usually zinc or magnesium, is placed in good electrical contact with the iron or steel. The more reactive metal is oxidised in preference to the iron, so it is gradually used up while the iron is protected.
For sacrificial protection, identify a metal more reactive than iron and explain that it oxidises instead of the iron.
A scratched paint coating may expose iron, whereas zinc can still give sacrificial protection at an exposed patch if it remains in contact with the iron.
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