The Solubility of Salts in Metals

A series of experiments to determine the solubilities of metal chlorides in their metals was carried out using a visual technique. The systems studied included Bi, Hg, Pb, Cd, Zn, Sn, In, Ag, and Cu with their chlorides. The results show that BiCl₃ and Hg₂Cl₂ are most soluble, the former being completely miscible with Bi at 778 °C, while the latter is soluble to the extent of 7 mole% at 600 °C. PbCl₂ is slightly soluble (1 mole% at 1,000 °C), while the remaining salts are considered insoluble in their metals. There does not appear to be any single criterion for predicting the solubility of salts in their metals. Experiments were also carried out to see if nonspecificity of solubility exists at high temperatures -i.e., to determine if metals dissolve salts other than their own halides. It was found that solubility does occur. It was also found that the less stable the salt, the greater is the solubility of the salt in a given metal, until the solubility approaches that of the salt of the metal. Thermodynamic calculations indicate that the solubility of a foreign salt in a metal can be explained in terms of oxidation-reduction reactions to form the halide of the metal, which in turn dissolves in the metal. These calculations suggest that BiCI₃ dissolves in bismuth metal as BiCl.