Question

Explain the following:

Concentrated nitric acid appears yellow when it is left standing in a glass bottle.

Answer 1

1. When concentrated nitric acid $\left({\mathrm{HNO}}_3\right)$is left standing in a glass bottle, thermal decomposition of a portion of nitric acid $\left({\mathrm{HNO}}_3\right)$takes place and reddish-brown coloured nitrogen dioxide $\left({\mathrm{NO}}_2\right)$ gas is produced.
2. The yellow colour of concentrated nitric acid $\left({\mathrm{HNO}}_3\right)$is due to the dissolution of reddish brown-colored nitrogen dioxide $\left({\mathrm{NO}}_2\right)$gas in it.