Ammonia

Ammonia molecule has an electronegative nitrogen atom bonded to three hydrogen atoms. Differences in electronegativity between nitrogen and hydrogen makes each hydrogen atom acquires positive charge. Thus, in the molecule, there is one negative site and three positive sites so that the molecules of ammonia associate through hydrogen bonding to form long chains.

Ammonia was known to mankind since a long period, as it was produced in nature by putrefying and ammonifying bacteria.

• Chemical compound, NH₃ colorless gas that is about one half as dense as air at ordinary temperatures and pressures. It has a characteristic pungent, penetrating odor.

• Ammonia forms a minute proportion of the atmosphere, found in volcanic gases and as a product of decomposition of animal and vegetable matter. Because ammonia was formerly obtained by destructive distillation of horns and hooves of animals, its water solution was called spirits of hartshorn. Ammonia has also been called alkaline air and volatile alkali.

• In 1774 Joseph Priestly first prepared ammonia as a separate gas by heating slaked lime with sal ammoniac and collected the gas over mercury. He called the gas alkaline air as it was found to be basic to litmus.

• In 1800, Davy established the basic composition and proved ammonia to be a compound of nitrogen and hydrogen.

• Two important resources of ammonia are ammonium salts and ammoniacal liquor obtained by the destructive destruction of coal .

• Ammonia and ammonium compounds are highly soluble in water and do not occur as minerals in large quantities.

• The NH₃ molecule has a large dipole moment, and this is consistent with its geometry, a triangular pyramid.

The polarity of NH₃ molecules and their ability to form hydrogen bonds explains the high solubility of ammonia in water. A chemical reaction also occurs when ammonia dissolves in water. In aqueous solution, ammonia acts as a base, acquiring hydrogen ions from H₂O to yield ammonium and hydroxide ions. Ammonia is a weak base.

A very strong solution of ammonia in water is liquor ammonia. It is obtained by boiling. It is used as a laboratory reagent. When cooled under pressure, ammonia condenses to a colourless liquid, which boils at -33.4^oC. This is liquid ammonia. It is used as a refrigerant.