The anion exchange of metal complexes. III. The cadmium-chloride system

The anion-exchange method described in the previous communications was applied to a study of the cadmium-chloride complex system. The distribution of the cadmium between Dowex-1 chloride resin and the solutions was measured by the "batch" method with the aid of the tracer Cd¹¹⁵. Formation of mononuclear complexes up to 10^-3 M cadmium was confirmed. The distribution curves were determined in the range 0.04 to 9.0 M lithium chloride and 0.01 to 9.4 M hydrochloric acid These curves coincided up to 0.2 M chloride. Above this concentration the hydrochloric acid curve is lower but both show a maximum around 4 M chloride. Construction of "ideal" distribution curves, valid for constant resinligand activity, made possible the evaluation of the complex system in terms of the species CdCl⁺, CdCl₂, CdCl₃^- and CdCl₄^2-, with HCdCl₃ forming also in hydrochloric acid. The successive formation constants found: log k₁* = 1.95, log k₂* = 0.55, log k₃* = -0.15 and log k₄* = -0.70, agree with published values. The acid dissociation constant of HCdCl₃ is about unity.