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

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


2 Answers

45 Points
9 years ago

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)


Aravind Bommera
36 Points
9 years ago

In the process of corrosion, due to the presence of air and moisture, oxidation takes place at a particular spot of an object made of iron. That spot behaves as the anode. The reaction at the anode is given by,

Electrons released at the anodic spot move through the metallic object and go to another spot of the object.

There, in the presence of H+ ions, the electrons reduce oxygen. This spot behaves as the cathode. These H+ ions come either from H2CO3, which are formed due to the dissolution of carbon dioxide from air into water or from the dissolution of other acidic oxides from the atmosphere in water.

The reaction corresponding at the cathode is given by,

The overall reaction is:

Also, ferrous ions are further oxidized by atmospheric oxygen to ferric ions. These ferric ions combine with moisture, present in the surroundings, to form hydrated ferric oxidei.e., rust.

Hence, the rusting of iron is envisaged as the setting up of an electrochemical cell.

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