Observe the following picture a write down the chemical reaction with explanation.
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 (Rust) on one part of iron surface while oxygen gets reduced to H2O in another part of surface. Different regions on the surface of iron become anode and cathode.
(1) Fe is oxidised to Fe2++ in the anode region
Fe(s) gives Fe2+(aq) + 2 e-
(2) O2 is reduced to form water in the cathode region.
O2(g) + 4H+(aq) +4e- gives 2H2O(l)
When Fe2+ ions migrate from the anode region they react with water and further get oxidised to form Fe3+ ions
A reddish coloured hydrated oxide is formed from Fe3+ ions. It is called rust. It collect on the surface.
2Fe3+( aq) + 4H2O(l) gives Fe2O3.H20(s)+ 6H(aq)
Because of various components of atmosphere oxidation of metals takes place, consequently resulting in their damage. This called 'corrosion'.
Iron rusts and a reddish coloured layer is collected on it. This is corrosion of iron