Explanation:
Nitrous acid is prepared in situ from hydrochloric acid and sodium nitrate because it is a weak acid and unstable. It only exists in an aqueous solution.
[tex]H^++NO_{2}^{-}\rightarrow HONO[/tex]
Nitrous acid is an unstable acid which gets decompose into the water , nitrogen dioxide and nitrogen monoxide gas.
[tex]2 HNO_2 \rightarrow NO_2 + NO + H_2O[/tex]
Whereas nitric acid is highly stable acid which can be easily prepared from its reagent and it can easily be stored for future use.
