Amphoteric Character of Hydroxides Considered in Analysis.
Self-Neutralization of Amphoteric Substances.
Hydrolysis of Salts
Ionization of Water.
[H+] × [HO−] / [Nonionized water] = KIon.
As the concentration of pure water, or of the water in dilute solutions, may be considered nearly a constant, we may put
[H+] × [HO−] = KH2O.
This is the relation most commonly, and most conveniently, used. It is free from all assumptions as to the molecular weight of the nonionized water, the calculation of the concentrations [p177] [H+] and [OH−] being independent of any such assumption. The value of KH2O increases decidedly with an increase in the temperature,[362] whereas the ionization constant of an ordinary acid, such as acetic acid, is affected very little by changes in temperature. This peculiar increase of the ionization of water at higher temperatures is undoubtedly due to the increasing dissociation of the complex water molecules into hydrol molecules (see p. [66]), which, presumably, are most easily ionized. Now, the value of the constant KH2O, at any temperature, may be determined in some half a dozen different and independent ways, including the conductivity method mentioned, and one of the most remarkable developments of the theory of ionization is that all of these methods lead to concordant results.[363]
Aside from considerations based on its ionization, water may be shown, by its chemical behavior, to have the functions of an acid and of a base, and the conclusions reached are in complete accord with those reached with the aid of the theory of ionization.