Question

Aluminum (E°Al3+/Al=−2.07 V) is more easily oxidized than iron (E°Fe3+/Fe=−0.477 V), and yet when both are exposed to the environment, untreated aluminum has very good corrosion resistance while the corrosion resistance of untreated iron is poor. What might explain this observation?

a) Aluminum has a protective oxide layer
b) Iron has a higher standard reduction potential
c) Aluminum has a lower ion concentration
d) Iron forms a strong bond with oxygen

Answer 1

Aluminum has better corrosion resistance than iron despite being more easily oxidized because it forms a protective oxide layer that prevents further corrosion.

The correct answer is a.

Step-by-step explanation:

The observation that aluminum (E°Al3+/Al=−2.07 V) is more easily oxidized than iron (E°Fe3+/Fe=−0.477 V) but still exhibits better corrosion resistance can be explained by aluminum's protective oxide layer. Although aluminum has a lower standard reduction potential and is therefore more reactive, when it is exposed to the environment, it rapidly forms a cohesive, impermeable oxide layer that adheres to the metal surface. This oxide layer acts as a barrier, preventing further oxidation and corrosion of the underlying aluminum. On the other hand, iron oxidizes to form rust, which is a flaky and porous oxide that allows oxygen and water to reach the metal surface, leading to further corrosion.

Corrosion of metals is a REDOX process. While galvanic corrosion can accelerate the rate at which iron corrodes when in contact with a more corrosion-resistant metal, aluminum remains protected due to its oxide film. This is why untreated aluminum has good corrosion resistance despite its higher reactivity compared to iron.