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Question
Give two chemical tests for nitric acid.
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Solution
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.
\[\ce{4HNO3 ->[\Delta] 2H2O + \underset{\text{Brown fumes}}{4NO2} + O2}\]
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