(i) Dilute nitric acid reacts with magnesium metal to liberate hydrogen gas which bums with a pale blue flame and a pop sound and magnesium nitrate is formed.
Mg + 2HNO3 (Dil) ⟶ Mg(NO3)2 + H2 ↑
(ii) Nitric arid when heated with copper turnings, produces brown fumes of nitrogen dioxide, which are passed over red hot iron filings. The residual gas collected over water is nitrogen.
(iii) Nitric arid, when heated alone, is decomposed into a reddish brown coloured gas nitrogen dioxide, steam and a colourless, odourless gas oxygen, which rekindles a glowing splinter.
4HNO3 ⟶ 4NO2 + 2H2O + O2
