Question

Give reasons corrosion is an electrochemical phenomena

Answer 1

Corrosion is defined as a chemical process where deterioration of metals occurs.

The most important type of corrosion is the electro-chemical corrosion of metals, where the oxidation process is facilitated by an electron acceptor, M → M+ + e–

Electrochemical corrosion occurs when electrons from the surface atoms are transferred to the suitable depolarizer or electron acceptor. It is important to have water as a medium.

 

The water droplets become the voltaic cell which is in contact with the metal and oxidizes it through a electrochemical process which enhances the rate of corrosion. The action of the electrochemical cell which is driven by the energy of oxidation helps in carrying forward the corrosion process.

 

Answer 2

The chemical attack upon the metal surface by oxygen , water or any other substances found in its immediate environment is termed as Corrosion.

example Rusting of iron.Tarnishing of silver.Corrosion of copper etc.

Corrosion of Metals is an Electrochemical process.
Explanation :

Rusting of iron causes iron to change into rust - an orange red powder material consisting mainly of hydrated iron[iii] oxide .
Rusting of iron takes place in presence of water and air.Corroding metal behaves as though it is part of a kind of an Electro chemical cell.
Millions of tiny Electrochemical cells come into action on the surface of iron exposed to moist air.
The presence of dissolved electrolytes in water accelerates the reaction.The more active sites on the iron surface acts as anodes and sites of impurities acts as anode.
At anode iron atom losses electrons and produces iron ions[Fe²⁺ (aq) ions.
Fe(s) ---> Fe²⁺(aq) + 2e 
the electron so produced move through metal to the cathode terminal  where they reduce oxygen in presence of H⁺ ions produced in dissociation of carbonic acid formed by dissolved CO2 in water.

At cathode:O2(g) +4H⁺(aq) +4e ---> 2H2O(i)

overall reaction
 2Fe(s) +O2(g) +4H⁺ (aq)--->2Fe²⁺[aq] +2H2O
Thus, Fe2+ ions formed at anode are further oxidized to Fe³⁺ ions by the atmospheric oxygen.
Fe2O3.xH2O formed we call it as Rust.