Question

Give reasons:

1. Pure nitric acid fumes in moist air

2. Nitric acid on exposure evolves traces of oxygen even at ordinary temperatures

3.The brown fumes of nitric acid are stronger when copper is added to nitric acid and heated than heated alone.

Answer 1

1. Pure nitric acid is highly reactive to moist air. It is oxidized in the presence of moist air to form nitrogen dioxide.

2. Nitric acid is a very strong oxidizing agent and therefore readily evolves oxygen even at room temperatures.

3. Nitrate ion oxidizes the copper metal to copper (II) ion while itself being transformed to NO₂ gas in the process:

Cu (s) + 4 H₃O⁺ (aq) + 2 NO₃^- (aq) --> [Cu(H₂O)₆]²⁺ (aq) + 2 NO₂ (g)