Solution phase thermodynamics of strong electrolytes based on ionic concentrations, hydration numbers and volumes of dissolved entities

Abstract

This article summarizes the successful restoration of Arrhenius’ theory of electrolytic dissociation founded 130 years ago. His idea of using the conductivity ratio for the degree of dissociation was a breakthrough in interpreting the properties of dilute solutions. For higher concentrations, as it was not satisfactory, attempts were being made to improve the methods of obtaining the degrees of dissociation. However, the latter was prematurely replaced by the empirical activity coefficient correction factors. Subsequently, the success of the Debye–Huckel (D–H) theory of inter-ionic interaction between free ions in explaining the properties of dilute solutions was taken to mean complete dissociation at all concentrations and interpretation of solution properties amounted to extending the D–H equations by the gradual addition of more parameters. At the end of six decades the equations became so complex that they failed to provide a unified interpretation of the causes of non-ideality at all concentrations and a molecular insight into the observed phenomena. Therefore, the present author abandoned them and started investigating the available experimental data as such. Using the degrees of dissociation and surface and bulk hydration numbers evaluated from solution vapour pressures, the author was able to interpret solution properties based on the idea due to Arrhenius a century earlier. Presented here is a comparison of the complicated equations based on complete dissociation with the simple equations obtained based on partial dissociation, hydration and volumes of entities in the solution. All the main equations are summarized in the table.