Question

Some metals form crusty oxide layers that can flake off to expose clean metal surfaces to moisture and air. Other metals form oxide layers that are durable and relatively impermeable. Use this fact to explain why aluminum, a more active metal than iron, is less susceptible to corrosion.

Answer 1

Aluminum is actually much more reactive than iron, and would corrode faster. In fact, it corrodes so fast that in forms a coating of aluminum oxide on any surface in contact with air. But since the surface is covered, it protects the rest of the metal, and it never corrodes deeper than a fraction of a millimeter. So technically, aluminum corrodes much faster, but much less completely because most of the mass of it is protected by the corroded layer.