Provide explanations for the following.
(a) In moist air, corrosion of iron is spontaneous. However, under anaerobic (O2 free) wet conditions, corrosion of iron is only marginally favoured.
(b) If iron is exposed to dry, gaseous O2, surface oxidation occurs but afterwards, the bulk iron is protected against further corrosion.

a) Corrosion of iron proceeds in the presence of oxygen and moisture

b) Formation of iron III oxide prevents further corrosion

Explanation:

Corrosion of iron refers to the formation of hydrated iron III oxide. Rust is commonly referred to as hydrated iron III oxide. In a wet oxygen free environment, there is no oxygen to combine with the iron to complete the electrochemical reaction of rusting.

Secondly, if the oxygen gas is dry, there is no electrolyte to set up the electrochemical reaction for corrosion of iron to take place. The oxide of iron is formed at the surface and this oxide layer prevents further corrosion of the iron hence the bulk of the iron is saved from corrosion.

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