Question -
Answer -
In the process of corrosion, dueto the presence of air and moisture, oxidation takes place at a particular spotof an object made of iron. That spot behaves as the anode. The reaction at theanode is given by,
Electrons released at the anodicspot 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+ ionscome either from H2CO3, which are formed due to thedissolution of carbon dioxide from air into water or from the dissolution ofother acidic oxides from the atmosphere in water.
The reaction corresponding at thecathode is given by,
The overall reaction is:
Also, ferrous ions are further oxidized by atmosphericoxygen to ferric ions. These ferric ions combine with moisture, present in thesurroundings, to form hydrated ferric oxide
i.e., rust.
Hence, the rusting of iron isenvisaged as the setting up of an electrochemical cell.