Influence of pressure on activity coefficients of electrolytes in solution

Abstract

Direct measurements have been made by the solubility method of the activity coefficient of potassium picrate in water at 25 °C, at atmospheric pressure and at a pressure of 200 MPa, in the presence of medium to high concentrations of added lithium chloride or lithium sulphate. The results, and others derived indirectly from earlier volumetric data on aqueous solutions of sodium chloride and potassium sulphate, show that the mean ionic activity coefficients increase appreciably when the pressure is raised, to an extent that increases as the ionic strength goes up. Part of the trend may arise from an enhanced dissociation, under pressure, of ion pairs in the concentrated solutions.