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

Q3.15: Explain how rusting of iron is envisaged as setting up of an electrochemical cell .

Solution:

In process of rusting, water molecules present at the layer of iron react with oxides and get dissociated and give H⁺ ions

 H₂O + CO₂    →        H₂CO₃

H₂CO₃                                ↔        2H⁺                 +          CO₃^2–

In present of H⁺ ions iron convert in Fe²⁺ so this part is act as anode

Reaction at anode:

Fe(s)               →        Fe²⁺(aq)         +          2e^–

Electron released at anodic spot move through the metals and go to another spot on the metal and reduce oxygen this spot act as cathode

Reaction at Cathode:

O₂(g)   +  4H⁺(aq)  +  4e⁺( aq)          →        2H₂O(l)

The overall reaction

2Fe(s)  + O₂(g)    +    4H⁺(aq)          →        2H₂O(l)  + Fe²⁺(aq)

Hence, rusting of iron act as electrochemical cell.