Question

Describe an experiment to show that nitric acid is an oxidising agent.

Answer 1

Nitric acid $\left({\mathrm{HNO}}_3\right)$ is an oxidizing agent:

• Nitric acid is an oxidizing agent which can be reduced in a variety of methods. Thus, it can be reduced to $\mathrm{NO},{\mathrm{NO}}_2,{\mathrm{N}}_2\mathrm{O}$ and other compounds.
• An oxidizing agent (also known as an oxidizer or an oxidant) is a chemical species that tends to oxidize other substances, causing them to lose electrons and hence raise their oxidation state.

Below reactions or experiments shows that nitric acid is an oxidizing agent:

• Carbon is oxidized to carbonic acid(${\mathrm{H}}_2{\mathrm{CO}}_3$) when heated with concentrated nitric acid(${\mathrm{HNO}}_3$), and the nitric acid is reduced to nitrogen dioxide (${\mathrm{NO}}_2$) and water (${\mathrm{H}}_2\mathrm{O}$).

$\underset{\mathrm{Carbon}}{\mathrm{C}}+\underset{\mathrm{Nitric}\mathrm{Acid}}{4{\mathrm{HNO}}_3(\mathrm{conc}.)}\to \underset{\mathrm{Carbonic}\mathrm{Acid}}{{\mathrm{H}}_2{\mathrm{CO}}_3}+\underset{\mathrm{Nitrogen}\mathrm{Dioxide}}{4{\mathrm{NO}}_2}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}$

• Here one mole of carbon interacts with 4 moles of nitric acid which acts as an oxidizing agent and reduces it to 4 moles of nitrogen dioxide.
• Sulphur is oxidized to sulphuric acid(${\mathrm{H}}_2{\mathrm{SO}}_4$) when heated with concentrated nitric acid(${\mathrm{HNO}}_3$), and the nitric acid is reduced to nitrogen dioxide and water.

$\underset{\mathrm{Sulphur}}{\mathrm{S}}+\underset{\mathrm{Nitric}\mathrm{Acid}}{6{\mathrm{HNO}}_3(\mathrm{conc}.)}\to \underset{\mathrm{Sulphuric}\mathrm{Acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4}+\underset{\mathrm{Nitrogen}\mathrm{Dioxide}}{6{\mathrm{NO}}_2}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}}$

• Here, one mole of sulphur interacts with 6 moles of nitric acid which acts as an oxidizing agent and reduces it to 6 moles of nitrogen dioxide.