Write a note on the corrosion of iron. Explain the chemistry of iron corrosion.

(N/A) Corrosion of iron is commonly known as rusting. It occurs in the presence of water and air.
Chemistry of corrosion: The chemistry of corrosion is complex,but it can be considered essentially as an electrochemical phenomenon.
Anode: At a particular spot on an iron object,oxidation takes place,and that spot behaves as an anode. The reaction is:
Oxidation: $2 Fe_{(s)} \rightarrow 2 Fe^{2+}_{(aq)} + 4 e^{-}$
$E^{\circ}_{(Fe^{2+}|Fe)} = -0.44 \ V$
Cathode: Electrons released at the anodic spot move through the metal to another spot,where they reduce oxygen in the presence of $H^{+}$ ions. These $H^{+}$ ions are formed due to the dissolution of carbon dioxide from the air into water,forming carbonic acid $(H_{2}CO_{3})$,or from other acidic oxides in the atmosphere. This spot behaves as a cathode with the reaction:
Reduction: $O_{2_{(g)}} + 4 H^{+}_{(aq)} + 4 e^{-} \rightarrow 2 H_{2}O_{(l)}$
$E^{\circ}_{(H^{+}|O_{2}|H_{2}O)} = 1.23 \ V$
Overall reaction: The overall reaction is the sum of the anodic and cathodic reactions:
$2 Fe_{(s)} + O_{2_{(g)}} + 4 H^{+}_{(aq)} \rightarrow 2 Fe^{2+}_{(aq)} + 2 H_{2}O_{(l)}$
The $Fe^{2+}$ ions are further oxidized by atmospheric oxygen to form hydrated ferric oxide,$Fe_{2}O_{3} \cdot xH_{2}O$,which is rust.