Question

Explain how rusting of iron is envisaged as setting up of an electrochemical cell.

Answer 1

The following processes occur on the surface of iron metal, which acts as an electrochemical cell.

Oxidation: \[\ce{Fe_{(s)} -> Fe^2+_{( aq)} + 2e-}\]

Reduction: \[\ce{O2_{(g)} + 4H+_{( aq)} + 4e- -> 2H2O_{(l)}}\]

Atmospheric oxidation: \[\ce{2Fe^2+_{( aq)} + 2H2O_{(l)} + 1/2 O2_{(g)} -> F2O3_{(s)} + 4H+_{( aq)}}\]

The water layer on the surface of iron dissolves acidic oxides in air, such as CO₂, forming acids that dissociate into H⁺ ions. The Fe loses electrons when exposed to H⁺ ions.

\[\ce{H2O + CO2 -> H2CO3 <=> 2H+ + CO^2-_3}\]