Question

What is the metallic corrosion? Give one example.

Answer 1

Corrosion is the process of solving degradation of metal by the action of gases and moisture present in the atmosphere due formation of chemical compounds.

Complete step by step answer:
The process of slow eating up of a metal by the action of gases and moisture present in air due to the formation of some chemical compounds is called metallic corrosion. The corrosion decreases the strength of a metal. Due to which highway bridges, gas/ liquid transmitted pipelines, waterways, railroads etc. gets every year which cause a great loss of money on this.
The most common example of corrosion is Rusting of iron.
The mechanism of rusting of iron can be explained on the basis of electrochemical theory. According to this theory, the formation of a small electrochemical cell (called corrosion cell) is formed on the surface of the metal.
Rusting following step.
(i) The water drops on the surface of iron dissolves $C{O_2}$ from air and forms carbonic acid which acts as electrolytic solution of the cell.
${H_2}O + C{O_2} \to {H_2}C{O_3} \rightleftharpoons 2{H^ + } + C{O_3}^{2 - }$
(ii) At a particular spot of iron, oxidation takes place and that spot behaves as anode.
$Fe(s) \to F{e^{2 + }}(aq) + 2{e^ - }$
(iii) The electrons lost at anode move through the metal to another site on the surface and reduce dissolved oxygen in the presence of${H^ + }$ions. This site acts as a cathode.
${O_2} + 4{H^ + } + 4{e^ - } \to 2{H_2}O$ $\begin{gathered} \\\ \\\ \end{gathered}$
The ferrous ions are oxidised by dissolved oxygen in water to form rust
$F{e_2}{O_3}.x{H_2}O$
$i.e.\;{\text{F}}{{\text{e}}^{{\text{2 + }}}}{\text{ + 2}}{{\text{H}}_{\text{2}}}{\text{O + }}\frac{1}{2}{O_2} \to F{e_2}{O_3}.x{H_2}O + {4^{H + }}$
Some more examples of corrosion is trashing of silver, development of green coating on copper and bronze etc.
The corrosion can be prevented by the following methods.
(A) By painting the surface of metal.
(B) By applying a thin film of oil or grease on it.
(C) By coating metal to prevent corrosion of the metal
(D) By using an anti rust solution.

Note:
More active metals are reality corroded. Presence of impurities in metals immersal the rate of corrosion. Air and moisture accelerate corrosion. Corrosion takes place. Readly bends scratches, dents and cuts in the metal.