Friday, May 24, 2013

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+                 +          CO32–
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.

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