Cambridge IGCSE Chemistry · Syllabus 0620 · Metals
Sacrificial Protection
What is Sacrificial Protection?
A method of preventing rust in which a more reactive metal is attached to iron or steel and is corroded in its place. The more reactive metal loses electrons in preference to the iron, so the iron does not form ions and does not rust; the attached metal is gradually eaten away and is replaced.
This definition is part of the Metals chapter in Cambridge IGCSE Chemistry.
Sacrificial Protection in context
Everything in Topic 9 hangs on one chain. A metal is a lattice of positive ions in a sea of delocalised electrons, and that structure gives the physical properties. Those properties decide what each metal is used for. Separately, metals can be put in order of how readily they react — the reactivity series — and that one position predicts a metal’s reactions with water, steam and acid, whether it can protect iron from rusting, and how hard it is to pull out of its ore. Extended candidates add a second layer to the same chain: reactivity is the tendency of an atom to form a positive ion, and that is what displacement reactions and sacrificial protection actually measure.
Common mistakes with Sacrificial Protection
- 20. “Sacrificial protection works because the zinc covers the iron and keeps water off it.” Supplement 9.5.5 Defect Describes the barrier mechanism and calls it sacrificial. Reason A zinc block bolted to a ship’s hull covers almost none of it, yet still protects. Covering is not the mechanism. Repair “Zinc is more reactive than iron, so it loses electrons in preference to the iron, and the iron is not oxidised.” Transfer What must be true of the connection between the two metals? They must remain in contact, so electrons can pass.