«The Ionization of Bases.»—The same relations hold for bases as for acids: the weaker bases give ionization constants as [p106] do the weaker acids; the strong bases, again, as was mentioned above, do not give constants. The values for strong bases, stated in the following table, are bracketed, and refer to the ionization in 0.1 molar solutions of the bases. Polyvalent bases, like polybasic acids, ionize in stages, and the primary ionization is usually stronger than the secondary ionization, and so forth. For instance, a study of ferric chloride solution shows that the third hydroxide group of ferric hydroxide, Fe(OH)_{ 3}, must have the smallest ionization constant.[193]
Base. Ratio. K. Potassium hydroxide [K^{ +}]×[HO^{ −}]/[KOH] (1) Sodium hydroxide [Na^{ +}]×[HO^{ −}]/[NaOH] (1) Barium hydroxide [Ba^{ 2+}]×[HO^{ −}]^2/[Ba(OH)_{ 2}] (0.03) Strontium hydroxide [Sr^{ 2+}]×[HO^{ −}]^2/[Sr(OH)_{ 2}] (0.03) Calcium hydroxide[B] [Ca^{ 2+}]×[HO^{ −}]^2/[Ca(OH)_{ 2}] (0.03) Ammonium hydroxide[C][D] [NH_{ 4}^{ +}]×[HO^{ −}]/ ([NH_{ 4}OH]+[NH_{ 3}]) 1.8E−5 Hydrazine[E] [N_{ 2}H_{ 5}^{ +}]×[HO^{ −}]/ ([N_{ 2}H_{ 5}OH]+[N_{ 2}H_{ 4}]) 0.3E−5 Aniline[F] [C_{ 6}H_{ 5}NH_{ 3}^{ +}]×[HO^{ −}]/ ([C_{ 6}H_{ 5}NH_{ 3}OH]+ [C_{ 6}H_{ 5}NH_{ 2}]) 0.5E−9 Water [H^{ +}]×[HO^{ −}]/[H_{ 2}O] at 25° 0.2E−15 at 100° 0.9E−14 [H^{ +}]×[HO^{ −}] at 25° 1.2E−14 at 100° 0.5E−11
A. As explained above, the bracketed values under K for strong bases are not constants, but express the values of the ratios for 0.1 molar solutions only. (For the alkaline earths 0.05 molar solutions are referred to.)
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°.
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.