Elucidation of Specific Reactions in Non-aqueous and Concentrated Electrolyte Solutions

Abstract

In non-aqueous solvents, alkali metal or alkaline earth metal ions as supporting electrolytes often cause specific or abnormal phenomena, much different from non-metallic (R₄N⁺) ions as the supporting electrolytes. The possible candidates of the specific phenomena are: (1) the changes in solvation conditions of the metallic cations, (2) the increase in Coulombic interaction between the metal cations and anions with decreasing permittivity, (3) possible adsorption of the metal ion, (4) liquid junction potential hard to be evaluated. However, many abnormal phenomena cannot be interpreted comprehensively based on only these factors. We have set up a hypothesis that the direct chemical interaction between alkali metal or alkaline earth metal and various anions (excluding ClO₄^- etc.), in non-aqueous solvents as well as aqueous solutions containing concentrated salts, could cause the abnormal phenomena. The hypothesis (the coordination ability of alkali metal or alkaline earth metal ions) has been successfully demonstrated not only by means of polarography, conductometry, and various spectroscopic technics, such as UV-visible, NMR, and Raman, but also with the assistance of reaction kinetics and theoretical calculations. Finally, we have succeeded in dissolving pure gold in the mixed solution between dilute nitric acid and the seawater.