[D] Corrected value, from Bredig's data, Z. phys. Chem., 13, 322 (1894). A. A. Noyes, Carnegie Institution, Publication No. 63, p. 178, finds the value 17.3E−6 for 18°.
[E] Uncorrected value, Bredig, ibid.
[F] Bredig, ibid.; Stieglitz and Derby, Am. Chem. J., 31, 457 (1904).
While the constants of a large number of organic bases[194] have been determined few constants of inorganic bases are as yet known. The fact that the majority of inorganic bases are polyvalent and difficultly soluble has made their examination in this respect more difficult. From the study of the decomposition of salts by water (see Chapter X), the trivalent bases, such as [p107] ferric hydroxide and aluminium hydroxide, are found to be much weaker than bivalent bases like cadmium, zinc and lead hydroxides,[195] but the data are not sufficient for the calculation of any constants, or for distinguishing between the ionization of the first, second and third hydroxide groups.
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.
| Molar Concentration. | Conductivity. | Per cent Ionized. | Ratio. |
|---|---|---|---|
| 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 |
The Ionization of Strong Electrolytes and the Law of Chemical Equilibrium.
It would lead too far from our subject to enter into a full discussion of this important question. It will be sufficient here to indicate two directions of inquiry, which promise to lead to an explanation of the apparent contradiction between the demands of the law of chemical equilibrium and the ionization of strong electrolytes.
In the first place, the law of chemical equilibrium is based thermodynamically, i.e. from the point of view of the ultimate energy relations involved, on the assumption that none but negligible forces of attraction or repulsion exist between the molecules, whose concentrations are factors in the equilibrium equations (cf. p. [95]).[200] Now, in solutions of electrolytes this condition is not strictly fulfilled under any circumstances; the attractions between ions of opposite charge and the repulsions of ions of like charge, as well as the effect of charged particles on neutral molecules, come into play. For strong electrolytes, where the proportion of charged particles is always a large one, the deviations from the simpler conditions to which alone the law is really applicable must be very much greater than for weak electrolytes. It is, therefore, probable that these electrical forces[201] are the source of the deviation of the ionization of strong electrolytes from the law of chemical equilibrium: although ionization is a reversible reaction, forces come into play which make the simple law inapplicable, and it is altogether likely, therefore, that we shall find, when all the factors have been investigated, that strong electrolytes should not and cannot obey this law alone.[202] In confirmation of this conclusion, recent careful calculations[203] have shown that entirely analogous deviations from the equilibrium law become perceptible in rather concentrated solutions of weak electrolytes, such as acetic acid, in which there is an accumulation of charged particles, more nearly akin to that present in dilute solutions of strong electrolytes. So it appears more and more certain that the deviations are a result of the presence of electrically charged components in the solutions, the amount of deviation depending on their concentration.