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.

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

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

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

The water layer on the surface of iron dissolves air's acidic oxides, such as \[\ce{CO2}\], forming acids that dissociate into \[\ce{H+}\] ions. \[\ce{Fe}\] loses electrons when exposed to \[\ce{H+}\] ions.

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