Cambridge O Level Chemistry · Syllabus 5070 · Metals
Protective Oxide Layer
What is Protective Oxide Layer?
A thin, tough, continuous layer of aluminium oxide that forms on the surface of aluminium in air. It sticks firmly to the metal and keeps air, water and acids away from it, so the metal beneath appears unreactive even though aluminium is high in the reactivity series.
This definition is part of the Metals chapter in Cambridge O Level Chemistry.
Common mistakes with Protective Oxide Layer
- 15. “Copper does not react with dilute acid because it has a protective oxide layer.” Defect Borrows aluminium’s explanation for a metal that does not need one. Reason Copper genuinely is unreactive towards dilute acid, because it sits below hydrogen. No barrier is involved. Repair “Copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from the acid.” Transfer Which metal does need the oxide-layer explanation, and why? Aluminium — because its position predicts a reaction that is not observed.
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