Question

When an iron nail is found in moist soil, it will have a coating of rust. This is an example of corrosion, the deterioration of metals by electrochemical processes. The reactions involved are as follows: Oxidation: Fe → Fe⁺² Reduction: O2 → H2O

The reaction occurs in an acidic medium. The H+ ions are supplied by H2CO3, which is formed when carbon dioxide reacts with water vapor. Complete and Balance the half reactions and give the overall balanced eqution.

Answer 1

Reduction half reaction:

$2O_{2(g)} + 4H^+_{(aq)} + 4e^- \to 2H_2O_{(l)} + O_{2(aq)}$

Oxidation half reaction:

$Fe_{(s)} \to Fe^{2+}_{(aq)} + 2e^-$

multiplying the oxidation half reaction by 2, we get the overall redox reaction to be;

$2Fe_{(s)} + 2O_{2(g)} + 4H^+_{(aq)}\to 2FeO.2H_2O_{(aq)}$

in acidic medium

and the general reaction is;

$2Fe_{(s)} + 2O_{2(g)} + 2H_2CO_{3(aq)}\to 2FeO.2H_2O_{(aq)} + 2CO_3^{2-}$