Complex ion formation and non-random mixing in molten reciprocal salt solutions

Abstract

Thermodynamic activities calculated from solution theories are compared with the values obtained from emf measurements and phase-diagram data on reciprocal molten salt solutions. For the systems examined (LiF-KCl and NaNO 3-AgCl) the experimental results are consistent with theory only if a correction for non-random mixing is included. Non-random mixing or “complexing” may result from coulombic forces (as in the LiF-KCl system) or non-coulombic forces (NaNO 3-AgCl) and in both cases, the description is conceptually similar. In dilute solutions of AgCl in molten alkali nitrates, for example, emf measurements can be accurately interpreted in terms of finite complex ions which have association constants that are relatively strongly dependent upon temperature. In more concentrated solutions the larger aggregates formed are less easily definable. In addition, the influence of non-random mixing on the solution properties in concentrated solutions, although significant, is relatively small and insensitive to temperature.