Question

Name the process responsible for the deposition of undesirable brown mass on the surface of iron nails in the presence of moist air.

Answer 1

Corrosion:

The gradual degradation of a metal when it is kept in contact with the environment is called corrosion. The metal atoms on the surface of the metal react with atmospheric gases like oxygen$\left({\mathrm{O}}_2\right)$, carbon dioxide$\left({\mathrm{CO}}_2\right)$, moisture$\left({\mathrm{H}}_2\mathrm{O}\right)$, sulfur dioxide $\left({\mathrm{SO}}_2\right)$ to convert the metal into its more stable form. These stable forms include oxides, sulfides, hydroxides, etc.

Corrosion on the surface of iron:

Iron (Fe) reacts with the oxygen in the air to form hydrated ferric oxide $\left({\mathrm{Fe}}_2{\mathrm{O}}_3·{\mathrm{xH}}_2\mathrm{O}\right)$ in the presence of moisture. The hydrated ferric oxide is called rust. This is an example of corrosion. This process is called rusting of iron, and the formation of rust can be given by the equation:

$$\begin{gathered} 4\mathrm{Fe}\left(\mathrm{s}\right)+3{\mathrm{O}}_2\left(\mathrm{g}\right)+{\mathrm{xH}}_2\mathrm{O}\to 2{\mathrm{Fe}}_2{\mathrm{O}}_3·{\mathrm{xH}}_2\mathrm{O}\left(\mathrm{s}\right) \\ \left(\mathrm{Rust}\right) \end{gathered}$$

The rust formed by corrosion is a brown solid, which gets deposited on the surface of the metal.

Therefore, the process by which a brown mass gets deposited on the surface of Iron nails is named as rusting of iron.