The rusting of iron is an oxidation process. The rust on iron does not form by a simple reaction between oxygen and iron surface. The rust is formed by an electrochemical reaction. Fe oxidises to Fe2O3. H2O on one part of iron surface while oxygen gets reduced to H2O on another part or surface, Different regions on the surface of iron become anode and cathode.
(1) Fe is oxidised to Fe2+ in the anode region.
Fe(s) → Fe2+ (aq) + 2e-
(2) O2 is reduced to form water in the cathode region.
O2(g) + 4H+ (aq) + 4e —→ 2H2O(I)
When Fe2+ ions migrate from the anode region they react with water and futher get oxidised to form Fe3+ ions.
A reddish coloured hydrated oxide is formed from Fe3+ ions. It is called rust. It collects on the surface
2Fe3+ (aq) + 4H2O(I) → Fe2O3. H2O(s) + 6H+ (aq)....
Because of various components in the atmosphere, oxidation of metals takes place, consequently resulting in their damage. This is called ‘corrosion’. Iron rusts and a reddish coloured layer is formed on it. This is corrosion of iron.
