Nitric acid is called also hard water.
Nitric acid is found in tiny amounts in the atmosphere and water rain, due to lightning, but it does not remain as such, combining with ammonia in the atmosphere, giving ammonium nitrate. Of the nitrates, the most important are: sodium nitrate (saltpeter of Chile), potassium (saltpeter from India) and calcium (saltpetre of Norway).
In laboratory, nitric acid is prepared from salts (natural nitrate) by treatment with hot concentrated sulphuric acid. The reaction takes place intwo stages:
I) NANO + H SO -> HNO + NaHSO
II) NANO + NaHSO -> HNO + Na SO
2NANO+ H SO -> 2HNO + Na SO
In pure state is colorless, pungent-smelling, with density 1.52. It dissolves in water, in any proportions, providing various concentrations of nitric acid. Nitric acid with a concentration of 96-98%, smokes in the air because it's vapors absorb moisture and give birth to a fog consisting of fine drops of liquid.
Concentrated nitric acid is colored yellow because dioxide carbon that is formed after partial decomposition in air, in presence of light and which remains dissolved in it:
4 HNO -> 4 NO + H 2 O + O ^
Therefore it should be stored in dark bottles and in darkness.Concentrated nitric acid, rich in NO, is called fuming nitric acid.
In aqueous solution ionizes as reversible reaction:
HNO + H O = [H O] + NO
This acid is one of the strongest, with a high degree of ionization.
With Nitric acid, copper reacts violently, forming copper nitrate, Cu (NO3) 2, nitrogen monoxide which oxidizes instantaneously into nitrogen dioxide and water. In the tube appears a suffocating gas, irritating, light reddish brown, due to nitrogen dioxide formed from the oxidation of nitrogen monoxide.
8HNO3 + 3Cu → 3Cu (NO3) 2 + 2NO + 4HNO3
2NO + O2 → 2NO2
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