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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 $Fe _2 O _3 . H _2 O$ on one part of iron surface while oxygen gets reduced to $H _2 O$ on another part or surface, Different regions on the surface of iron become anode and cathode.
(1) $Fe$ is oxidised to $Fe ^{2+}$ in the anode region.
$
Fe _{( s )} \rightarrow Fe ^{2+}{ }_{( aq )}+2 e ^{-}
$
(2) $O _2$ is reduced to form water in the cathode region.
$
O _{2(g)}+4 H ^{+}( aq )+4 e -\rightarrow 2 H _2 O _{(1)}
$
When $Fe ^{2+}$ ions migrate from the anode region they react with water and futher get oxidised to form $Fe ^{3+}$ ions.
A reddish coloured hydrated oxide is formed from $Fe ^{3+}$ ions. It is called rust. It collects on the
surface.
$2 Fe ^{3+}( aq )+4 H _2 O _{( l )} \rightarrow Fe _2 O _3 \cdot H _2 O _{( s )}+6 H ^{+}( aq ) \cdots$
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.
(1) $Fe$ is oxidised to $Fe ^{2+}$ in the anode region.
$
Fe _{( s )} \rightarrow Fe ^{2+}{ }_{( aq )}+2 e ^{-}
$
(2) $O _2$ is reduced to form water in the cathode region.
$
O _{2(g)}+4 H ^{+}( aq )+4 e -\rightarrow 2 H _2 O _{(1)}
$
When $Fe ^{2+}$ ions migrate from the anode region they react with water and futher get oxidised to form $Fe ^{3+}$ ions.
A reddish coloured hydrated oxide is formed from $Fe ^{3+}$ ions. It is called rust. It collects on the
surface.
$2 Fe ^{3+}( aq )+4 H _2 O _{( l )} \rightarrow Fe _2 O _3 \cdot H _2 O _{( s )}+6 H ^{+}( aq ) \cdots$
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.
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