Excess pressures for aqueous solutions

Abstract

Gibson's concept of an excess pressure is applied to an analysis of the properties of solutions containing both salts and neutral solutes. Definitions of excess pressures are examined in terms of volumes occupied by one mole of solute and one mole of solvent in solution, and in terms of partial molar and apparent molar volumes of solute and solvent. A distinction is drawn between occupied volumes and partial molar volumes and between excess pressures which characterise solute–solvent interactions and excess pressures which include contributions from solute–solute interactions in real solutions. Descriptions of excess pressures in terms of the effect of solute on a solvent is linked to the description in terms of a structural temperature along the lines proposed by Bernal and Fowler. Excess pressures are calculated for aqueous solutions containing (a) sodium chloride, (b) tetrabutylammonium bromide, (c) urea, (d) t-butyl alcohol, (c) DMSO and (d) hydrogen peroxide.