Question

Explain why, though aluminium is more reactive than iron, yet there is less corrosion of aluminium when both are exposed to air.

Answer 1

Aluminium is more reactive than iron and quickly reacts with oxygen to form a thin layer of aluminium oxide (Al₂O₃) on its surface. This oxide layer is non-porous, tough, and tightly adheres to the metal, acting as a barrier that prevents further air and moisture from penetrating deeper.

On the other hand, when iron reacts with moist air, it forms a porous, flaky layer of iron oxide (rust). This layer crumbles and falls off easily, continuously exposing the fresh iron beneath to the environment and allowing corrosion to propagate throughout the metal. Thus, aluminium effectively protects itself from ongoing corrosion, while iron does not.