Modern inorganic chemistry

90 ACIDS AND BASES: OXIDATION AND REDUCTION

OTHER CONCEPTS OF ACIDS AND BASES

Liquid ammonia (p. 216), like water, is very slightly dissociated, and

shows a very small electrical conductance :

+ NHJ

cf. 2H 2 O^-H 3 O+ + OH"

By analogy, ammonium salts should behave as acids in liquid
ammonia, since they produce the cation NH^ (the 'solvo-cation'),
and soluble inorganic amides (for example KNH 2 , ionic) should act
as bases. This idea is borne out by experiment ; ammonium salts in
liquid ammonia react with certain metals and hydrogen is given off.
The neutralisation of an ionic amide solution by a solution of an
ammonium salt in liquid ammonia can be carried out and followed
by an indicator or by the change in the potential of an electrode,
just like the reaction of sodium hydroxide with hydrochloric acid in
water. The only notable difference is that the salt formed in liquid
ammonia is usually insoluble and therefore precipitates.
Other liquid inorganic compounds show the wauto-dissociation'
characteristic of water and liquid ammonia ; for example, dinitrogen
tetroxide (p. 23 1 ), as well as undergoing the more familiar homolytic
dissociation
heat
N 204 ^=±cool

can also dissociate thus :

i.e. a heterolytic dissociation, giving ions, and therefore producing a
slight electrical conductance. By analogy, compounds containing
the ion NO "*" (the nitrosyl cation) should behave as acids and nitrates
as bases in liquid dinitrogen tetroxide. The neutralisation reaction

NOC1 + KNO 3 -> KC1 4- N 2 O 4

nitrosyl chloride potassium salt solvent

(acid) nitrate

(base)

does in fact occur in liquid dinitrogen tetroxide. Just as some metals
dissolve in water or alkali to give off hydrogen and yield hydroxides.
metals can dissolve in dinitrogen tetroxide to give off nitrogen
oxide and yield nitrates; this type of reaction has been used to
produce an anhydrous nitrate of copper(II) which has unexpected
properties (p. 41 3).