The difference in ionization and in chemical activity between a strong base, like sodium or potassium hydroxide, and a weak base, like ammonium hydroxide, has already been discussed and illustrated (see p. 77). In analysis, advantage is frequently taken of these relations.[196]
«The Ionization of Salts.»—While we read and hear a good deal about strong and weak acids, and strong and weak bases, the expression "strong" or "weak" salt is never heard; as a matter of fact, all salts, with very few exceptions, ionize exceedingly readily—about as readily as the strongest acids and bases. There are minor differences, but none of great moment—none of the kind indicated by the wide range of constants for the acids and bases. There are only a few important exceptions to this general rule—the most important ones, among the common salts, being mercuric chloride and mercuric cyanide: their exceptional behavior in regard to ionization, as indicated by their conductivities (see below), is found side by side with an exceptional chemical behavior, exactly as the theory of ionization would lead us to anticipate, and it renders necessary certain precautions, particularly in analytical work, which will be discussed later (Chap. VI). Ordinary salts are all ionized readily: for instance, whereas acetic acid in molar solution is ionized only to the extent of 0.37 per cent, its salts are highly ionized, the degree of ionization of sodium acetate, for example, being 52.8% in molar solution. As in the case of the strong acids and bases, salts of the type MeX, which ionize according to the equation MeX ⇄ Me^{ +} + X^{ −} and which, according to the law of chemical equilibrium, might be ‹expected› to give a constant ratio [Me^{ +}][X^{ −}] / [MeX], do ‹not› give a ‹constant ratio›. That is, when the values obtained for the concentrations of the ions and of the nondissociated molecules, in solutions of various [p108] strengths, are substituted in this formula, different values are obtained.[197] For potassium chloride, we have the following relations:
Molar Per cent Ratio. Concentration. Conductivity. Ionized. 0. 131.2 100 — 0.001 127.6 97.3 0.035 0.01 122.5 93.4 0.130 0.05 115.9 88.4 0.335 0.10 111.9 85.1 0.485 0.20 107.7 82.1 0.754 0.50 102.3 77.9 1.38 1.00 98.2 74.9 2.23