Q15 of 33 Page 90

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

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


Fe(s) ⇒ Fe2+ (aq) + 2e-


Electrons released at the anodic spot move through the metal and go to another spot of the object, wherein 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 the air into water. The cathodic reaction is given by


O2(air) + 4H(aq)++4e-⇒ 2H2O


The overall reaction is given by,


2Fe(s) + O2(air) + 4H(aq)+⇒ 2Fe2++2H2O


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Arrange the following metals in the order in which they displace each other from the solution of their salts.

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