Question

What is corrosion give two examples?

Answer 1

Corrosion:

• The slow degradation of the metal due to the effect of air, water or any chemical reaction is called corrosion.
• During the process of corrosion, the metal gets acted upon by moisture and oxygen present in the air and gets converted into its oxide.

Example:

Tarnishing of silver utensils:

• When Silver utensils are exposed to air, they react with the Sulphur gas present in the atmosphere which leads to the formation of silver sulphide which is black in colour.
• The chemical reaction can be represented as:

$\underset{\mathrm{Silver}}{2\mathrm{Ag}\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrogen}\mathrm{sulphide}}{{\mathrm{H}}_2\mathrm{S}\left(\mathrm{g}\right)}\to \underset{\mathrm{Silver}\mathrm{sulphide}}{{\mathrm{Ag}}_2\mathrm{S}\left(\mathrm{s}\right)}+\underset{\mathrm{Hydrogen}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$

Corrosion of aluminium:

• Aluminium when exposed to air forms a white thin layer of oxide $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ on its surface.
• The chemical reaction can be represented as:

$\underset{\mathrm{Aluminium}}{4\mathrm{Al}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{3{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Aluminium}\mathrm{oxide}}{2{\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}$