Solvent structural constant and solvation behaviour applied to the description of aqueous electrolytes at 25–300 °C

Abstract

From the application of a solvent structural constant and calculations of ‘free’water remaining after solute solvation, water activities are described at temperatures up to 300 °C for NaCl solutions and at 25 °C for other electrolyte solutions. Ionization constants for NaCl are also obtained. The concentration of free (non-solvating) water is proportional to the activity of water (derived from vapour pressures) raised to a power B, which is a temperature independent constant (6.67) believed to represent a structural property of the solvent. The solute–solvent mass-action equilibrium appears to be predominantly a function of the density of water in the immediate vicinity of each solvated solute species, rather than of the bulk concentration of free water. Relative solvation numbers obtained for univalent ions quantitatively agree with expectations. Thus a model with all parameters defined to have chemical significance describes reasonably well the activity of water over aqueous electrolyte solutions.