1.

What happens when nitric acid is dropped on pumice stone?

Answer»

When conc. HNO3 is dropped on red-hot pumice stone a brown gas mixture evolves. When this gas mixture is passed through a 'U' tube dipped in a freezing mixture a yellow coloured liquid and a colourless gas is obtained. This gas is oxygen as it is completely absorbed by alkaline pyrogallate solution brown. Hence, nitric acid contains oxygen

4HNO3=4NO2+2H2O+O2

When nitric acid is dropped over heated saw dust (pumice stone) it catches fire spontaneously , i.e., bursts into flame.



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