Question

Give reasons for the following:
Commercial concentrated nitric acid is yellow in colour, but when it is diluted with water, it turns colourless.
Give one chemical test for nitric acid.

Answer 1

Concentrated nitric acid contains dissolved nitrogen dioxide that imparts it a yellowish brown colour. When diluted in water, nitrogen dioxide is converted into nitric acid, which is colourless in its pure form.
The chemical test for nitric acid is to heat the acid. Release of brown fumes of nitrogen dioxide confirms the presence of nitric acid.