Nitric acid

Nitric acid is a chemical with the formula HNO₃.

Nitric acid
The model of a nitric acid molecule.
Properties
Appearance	Colorless liquid
Melting Point	−42 °C (−44 °F; 231 K)
Boiling Point	83 °C (181 °F; 356 K)
Solubility in water	Miscible
Density	1.51 g/cm3
pKa	-1.4

Production

Nitric acid is usually produced industrially through the Ostwald process, which is based on the Haber process of producing ammonia. In the first step, the ammonia is oxidized to nitrogen monoxide(NO):
${\ce {4 NH3 + 5 O2 = 4 NO + 6 H2O}}$
The nitrogen monoxide is then oxidized by oxygen to form nitrogen dioxide(NO₂):
${\ce {2 NO + O2 = 2 NO2}}$
Finally, the nitrogen dioxide is dissolved in water to form the final product:
${\ce {3 NO2 + H2O = 2 HNO3 + NO}}$

In laboratories, nitric acid can be prepared by reacting nitrate salts with sulfuric acid(H₂SO₄):
${\ce {NaNO3 + H2SO4 = HNO3 + NaHSO4}}$

Properties

Physical Properties

Anhydrous nitric acid is a colorless liquid at room temperature. Sometimes, nitric acid may look yellow or red because of the nitrogen dioxide dissolved in it. At high concentrations(>95%) it's called fuming nitric acid or red fuming nitric acid since it gives off brown fumes of nitrogen dioxide. Very pure nitric acid(99.99%) is called white fuming nitric acid.

Chemical Properties

Nitric acid is a strong oxidizing acid. It can even oxidize relatively unreactive metals like Silver and Copper. Its pKa is less than -1.

Very dilute nitric acid reacts with metals and releases hydrogen:
${\ce {Mg + 2 HNO3 = Mg(NO3)2 + H2 ^}}$
Dilute nitric acid is usually reduced to Nitrogen monoxide(NO) when reacting with metals:
${\ce {3 Cu + 8 HNO3 = 3 Cu(NO3)2 + 2 NO ^ + 4 H2O}}$
The reaction of concentrated nitric acid with metals usually results in the release of nitrogen dioxide(NO₂) gas:
${\ce {Cu + 4 HNO3 = Cu(NO3)2 + 2 NO2 ^ + 2 H2O}}$

Nitric acid can also oxidize non-metals like graphite:
${\ce {C + 4 HNO3 = CO2 ^ + 4 NO2 ^ + 2 H2O}}$

When exposed to light, nitric acid decomposes:
${\ce {4 HNO3 = 2 H2O + 4 NO2 ^ + O2 ^}}$

Applications

Nitration

Nitration is a process which chemicals into nitric acid and sulfuric acid. The nitric acid will remove the hydrogen ions of the substance and replace them with nitronium ions which makes it highly explosive. The sulfuric acid is used to absorb water that forms during the reaction. This process is used for making explosives such as TNT or Nitrocellulose.

Others

Nitric acid can be used as an oxidizing agent or a rocket propellant. It can also be used to convert metals to their oxidized form.