Question

Identify the acid which matches the following description:

The acid which is prepared by catalytic oxidation of ammonia.

Answer 1

Catalytic oxidation of ammonia $\left({\mathrm{NH}}_3\right)$:

• When ammonia gas and oxygen are passed over heated platinum, a catalyst, ammonia is oxidized to form colorless nitric oxide $\left(\mathrm{NO}\right)$. When this gas comes in contact with air, it turns brown.
• $4{\mathrm{NH}}_3\left(\mathrm{g}\right)+5{\mathrm{O}}_2\left(\mathrm{g}\right)\underset{800°\mathrm{C}}{\stackrel{\mathrm{Pt}\text{gauze}}{⟶}}4\mathrm{NO}\left(\mathrm{g}\right)+6{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+\text{Heat}$
  The colorless nitric oxide $\left(\mathrm{NO}\right)$ is further oxidized to give dark brown fumes of nitrogen dioxide $\left({\mathrm{NO}}_2\right)$
• $2\mathrm{NO}\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)⟶2{\mathrm{NO}}_2\left(\mathrm{g}\right)$
  This ${\mathrm{NO}}_2$ reacts with water to produce a mixture of nitric acid $\left({\mathrm{HNO}}_3\right)$ and nitrous acid $\left({\mathrm{HNO}}_2\right)$.
• $2{\mathrm{NO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)⟶{\mathrm{HNO}}_3\left(\mathrm{aq}\right)+{\mathrm{HNO}}_2\left(\mathrm{aq}\right)$

Therefore, a mixture of nitric acid and nitrous acid is prepared by catalytic oxidation of ammonia.