Nitric acid can also be prepared entirely from the air. Air free from moisture and carbon dioxide is subjected to an electric arc whose temperature is around 3000oC. At this temperature, nitrogen and oxygen of the air combine to form nitric oxide.
The nitric oxide so formed is then mixed with more air to form nitrogen dioxide.
Then nitrogen dioxide along with air is dissolved in water to form nitric acid.
Remember:-
Fuming nitric acid is concentrated nitric acid that has a deep brown colour due to considerable amount of nitrogen dioxide present in it. When exposed, some of the nitrogen dioxide escapes and hence the name "fuming nitric acid" is given to it.
It is prepared by distilling concentrated nitric acid with a small quantity of starch. It is a far more powerful oxidizing agent than ordinary nitric acid.
