Explain the following:
Concentrated nitric add appears yellow when it is left standing in a glass bottle.
Although pure concentrated nitric acid is colorless, it appears yellow when left standing in a glass bottle due to the dissolution of reddish brown nitrogen dioxide gas in the acid. Nitrogen dioxide is produced because of the thermal decomposition of a portion of nitric acid.
4HNO3 → 2H2O + 4NO2 + O2