Question

Why commercial sample of nitric acid is pale yellow in colour?

Answer 1

• The pure form of nitric acid $\left({\mathrm{HNO}}_3\right)$ is colorless. The thermal decomposition of nitric acid produces nitrogen dioxide(${\mathrm{NO}}_2$), which imparts yellowish color to nitric acid.

$\Rightarrow 4{\mathrm{HNO}}_3\left(\mathrm{aq}\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+4{\mathrm{NO}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)$