Question

Observe the following picture and write down the chemical reaction with explanation.

Answer 1

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 $F{e}_2{O}_3.2H_{2}O$ 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 $F{e}^{2+}$ in the anode region.

$F{e}_{\left(s\right)}⟶F{e}_{\left(aq\right)}^{2+}+2e^{-}$

(2) $O_2$ is reduced to form water in the cathode region.

$O_{2\left(g\right)}+4H_{\left(aq\right)}^{+}+4e^{-}⟶2H_2{O}_{\left(l\right)}$

When $F{e}^{2+}$ ions migrate from the anode region they react with water and further get oxidised to form $F{e}^{3+}$ ions.

A reddish coloured hydrated oxide is formed from $F{e}^{3+}$ ions. It is called rust. It collects on the surface.

$2F{e}_{\left(aq\right)}^{3+}+4H_2{O}_{\left(l\right)}⟶F{e}_2{O}_3.H_2{O}_{\left(s\right)}+6H_{\left(aq\right)}^{+}$

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.