How to identify Nitric acid?
Detection of nitric acid: When some copper ingot mixed with concentrated nitric acid is heated in a test tube, brown nitrogen dioxide gas is evolved and the solution in the test tube turns blue due to the formation of copper nitrate.
Cu + 4HNO3 = Cu (NO3)2 + 2NO2 ↑ + 2H2O
How to identify Nitric acid by Ring test?
A small amount of dilute Nitric acid (HNO3) is added to a test tube with freshly prepared Ferrous sulphate solution. The test tube is cooled with cold water. Now concentrated sulfuric acid (H2SO4) from another test tube is poured very slowly down the tube into the first test tube. H2SO4 is heavy and sinks to the bottom of the solution.
In this condition, a brown-coloured ring is formed at the junction of the two liquid layers. This is called the Brown Ring Test. Nitric acid and nitrate salts can be detected by this Brown Ring test.