225The nitrate ion. The net charge of the whole ion is 1−.
This arrangement is commonly used as an example of resonance. Like the isoelectronic carbonate
ion, the nitrate ion can be represented by resonance structures:
Properties
Almost all inorganic nitrate salts are soluble in water at standard temperature and pressure. A
common example of an inorganic nitrate salt is potassium nitrate (saltpeter).
In organic chemistry a nitrate (not to be confused with Nitro or Nitrite) is a relatively rare functional
group with general chemical formula RONO 2 where R stands for any organic residue. They are the
esters of nitric acid and alcohols formed by nitroxylation. Examples are methyl nitrate formed by
reaction of methanol and nitric acid, the nitrate of tartaric acid, and the inaccurately named
nitroglycerin (which is actually an organic nitrate compound, not a nitro compound).
Like organic nitro compounds (see below) both organic and inorganic nitrates can be used as
propellants and explosives. In these uses, the thermal decomposition of the nitrate yields molecular
nitrogen N 2 gas plus considerable chemical energy, due to the high strength of the bond in
molecular nitrogen. Especially in inorganic nitrate reactions, oxidation from the nitrate oxygens is
also an important energy-releasing process.
Occurrence
Nitrate compounds are found naturally on earth as large deposits, particularly of Chile saltpeter a
major source of sodium nitrate.
Nitrites are produced by a number of species of nitrifying bacteria, and the nitrate compounds for
gunpowder (see this topic for more) were historically produced, in the absence of mineral nitrate
sources, by means of various fermentation processes using urine and dung.
Uses
Nitrates are mainly produced for use as fertilizers in agriculture because of their high solubility and
biodegradability. The main nitrates are ammonium, sodium, potassium, and calcium salts. Several
million kilograms are produced annually for this purpose.
Other Uses
The second major application of nitrates as oxidizing agents, most notably in explosives where the
rapid oxidation of carbon compounds liberates large volumes of gases (see Gunpowder for an
example). Sodium nitrate is used to remove air bubbles from molten glass and some ceramics.
Mixtures of the molten salt are used to harden some metals.