Rusting of Iron

Corrosion of iron is an electro chemical process. Iron under goes redox reaction in presence of air or water to form iron (III) oxide (Fe$_2$O$_3$ . nH$_2$O) called rusting of iron. Rusted surface of iron provide no protection to underlying iron and eventually convert whole iron into reddish brown rust. Rusting occurs at different places of metal surface. A metal surface area of less moisture act as anode and oxidizes iron in this region.

The chemical equation for the rusting of iron is as follows:

Fe → Fe$^{+2}$ + 2e$^–$

Metal surface with high moisture content act as cathode and reduces atmospheric oxygen to hydroxide ions

Metal surface with high moisture content act as cathode and reduces atmospheric oxygen to hydroxide ions $OH^{-1}$

${O2 + 2H_2O + 4e \longrightarrow 4 OH{^{-1}}}$

The ${Fe{^{+2}}}$ ions further reacts with oxygen to form rust Iron (III) oxide

(${Fe2O3. n H2O}$).