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Question
Observe the following picture a write down the chemical reaction with the explanation.
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Solution
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.XH2O (Rust) is on one part of the iron surface, while oxygen gets reduced to H2O in another part of the surface. Different regions on the surface of iron become anode and cathode.
(1) Fe is oxidised to Fe2+ in the anode region.
\[\ce{Fe(s) -> Fe^{2+}(aq) + 2e^-}\]
(2) O2 is reduced to form water in the cathode region.
\[\ce{O2(g) + 4H^+(aq) + 4e^- -> 2H2O(l)}\]
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 collects on the surface.
\[\ce{2Fe^{3+}(aq) + 4H2O(l) -> Fe2O3.H2O(s) + 6H^+(aq)}\]
Due to various components of the atmosphere, oxidation of metals takes place, consequently resulting in their damage. This is called 'corrosion'. Iron rusts, and a reddish-coloured layer is collected on it. This is the corrosion of iron.
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