Answer:
Explanation:
Oxygen gas and water must be present for iron to rust.
A region of the metal’s surface serves as the anode, where oxidation
occurs:
Fe(s) → Fe²⁺ (aq) + 2 e⁻
The electrons given up by iron reduce atmospheric oxygen to water at the cathode, which is another region of the same metal’s surface:
O₂ (g) + 4H⁺ (aq) + 4 e⁻ → 2 H₂O (l)
The overall redox reaction is:
2 Fe(s) + O₂(g) → 4H⁺(aq) + 2Fe²⁺ (aq) + 2 H₂O(l)
The Fe²⁺ ions formed at the anode are further oxidized by oxygen:
4 Fe²⁺ (aq) + O₂(g) 1 (4 + 2x) H₂O (l) → 2 Fe₂O₃ . xH₂O(s) + 8 H⁺(aq)
This hydrated form of iron(III) oxide is known as rust. The amount of water associated with the iron oxide varies, so we represent the formula as 2 Fe₂O₃ . xH₂O.
