Question

Explain with the help of a balanced equation, the brown ring test for nitric acid.

Answer 1

Brown ring test -
Nitric acid in a test tube is taken and then 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.

\[\ce{6FeSO4 + 3H2SO4 + 2HNO3 -> 3Fe2(SO4)3 + 2NO + 4H2O}\]

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