production of Nitric acid

Nitric acid is made by reacting nitrogen dioxide (NO2) with water.
3 NO2 + H2O → 2 HNO3 + NO
Normally, the nitric oxide produced by the reaction is reoxidized by the oxygen in air to produce additional nitrogen dioxide.
In laboratory, nitric acid can be made from copper(II) nitrate or by reacting approximately equal masses of a nitrate salt with 96% sulfuric acid (H2SO4), and distilling this mixture at nitric acid's boiling point of 83 °C until only a white crystalline mass, a metal sulfate, remains in the reaction vessel.
H2SO4 + NO3 → HSO4(s) + HNO3(g)
For many years nitric acid was made by the reaction of sulfuric acid and saltpeter, but this method is no longer used.
NaNO3 + H2SO4 → NaHSO4 + HNO3
Nitric acid is now manufactured by combusting ammonia in air in the presence of a (platinum or other noble metal) catalyst, and the nitrogen oxides thus formed are oxidized further and absorbed in water to form nitric acid.
NH3 + 2O2 → HNO3 + H2O