How rusting of iron is envisaged as setting up of an electrochemical cell?
Solution)
Rusting of Iron is due to corossion.
Rust is an Fe2O3.xH2O
Theory of Rusting :
1. Water present on the metal surface dissolves CO2 and O2 from the air.
H2O + CO2 ---------> H2CO3
O2 + 4H+ + 4e- -------> 2H2O
2. Fe in contact with dissolved CO2 and O2 undergoes oxidation.
Fe ------------> Fe2+ + 2e- Anode (EFe+2/Fe = -0.44V)
3. Electrons lost by Fe are taken by H+
H+ + e- ------------> H
4H+O2 --------> 2H2O
The dissolved O2 can be take electrons directly also
O2 + 2H2O + 4e- -----------> 3OH- cathode
Overall 2Fe(s) + O2(g) +4H+ (aq) -------------> 2Fe+2 + 2H2O
4. Fe+2 react with dissolved O2 and water
Fe+2 + 2OH- -----------> Fe(OH)2
4Fe(OH)2 + O2 +2H2O ----------> 4Fe(OH)3
2Fe(OH)3 ---------> Fe2O3 + 3H2O
Fe2O3 + XH2O ------------> Fe2O3.XH2O
Rust (Hydrated ferric oxide)