Question

Why does conc. Hno3 kept in a bottle turn yellow in colour?

Answer 1

Nitric acid takes yellowish browncolour due to the presence of dissolved nitrogen dioxide. Nitric acidslowly decomposes even at room temperature, specially in the presence of sunlight. Liberated nitrogen dioxide dissolves in the acid and gives ayellow colour.

Answer 2

Conc HNO3 forms No2 even at room temperature which is brown colour gas and it remains in the HNO3 and give it a yellow colour.

4HNO3 → 4 NO2 + 2H2O + O2