Question

Give two chemical tests for nitric acid.

Answer 1

Two tests for nitric acid are-
(i)  Brown ring test : 
Nitric acid in a test tube is taken and then freshly prepared ferrous sulphate solution is added. Concentrated H₂SO₄ is then added carefully down the sides of the test tube, dark brown ring is formed at the
junction of two layers.

\[\ce{6FeSO4 + 3H2SO4 + 2HNO3 -> 3FE2(SO4)3 + 2NO + 4H2O}\]

\[\ce{FeSO4 + NO + 5H2O -> \underset{\text{Hydrated nitrosoferrous Sulphate(brown ring)}}{[Fe(NO)(H2O)5]SO4}}\]

(ii) Nitric acid on heating gives brown fumes of nitrogen dioxide.
\[\ce{4HNO3  ->[\Delta] 2H2O + \underset{\text{Brown fumes}}{4NO2} + O2}\]