Water and other hydroxylic solvents both donate and accept protons with reasonable facility and are
termed amphiprotic.
Non-ionizing Solvents
The major uses of non-ionizing solvents in chemical analysis are twofold. They may be used simply to
provide media for the dissolution and reaction of covalent materials, or they may play a more active
part in a chemical process. For example, oxygen-containing organic solvents can be used to effect the
solvent extraction of metal ions from acid aqueous solutions; the lone pair of electrons possessed by the
oxygen atom forming a dative bond with the proton followed by the extraction of the metal ion as an
association complex.
This process is discussed more fully in Chapter 4.
3.3—
Acid–base Equilibria
The Lowry–Brønsted concept provides a basis for the interpretation of reactions in protonic solvents.
This concept may be summarized by considering the generalized equilibrium
where AH and B represent the acid and base for the forward reaction and A– and BH+ the conjugate
base and conjugate acid for the reverse reaction. Thus the dissociation of a typical acid in water may be
represented by
with the water acting as a base and H 3 O+ being the conjugate acid. The equilibrium constant is given by
and is known as the acid dissociation constant. In the case of a base a parallel treatment may be used in
which the water acts as an acid
and Kb, the base dissociation constant, is given by
The solvent term [H 2 O] varies by a negligible amount in such reactions and