Application of the multicomponent Gibbs-Duhem equation for the activity coefficient evaluation of a ternary aqueous solution with an electrolyte and a molecular solute from osmotic coefficient data

Abstract

Starting from the solution of the Gibbs-Duhem equation for multicomponent systems on terms of the osmotic coefficient, a method was developed to evaluate the activity coefficients of the electrolytic and molecular solutes of a ternary aqueous solution. An analytical expression of the osmotic coefficient was proposed for the accurate description of experimental data, which is in agreement with the behaviour of the binary systems at the corresponding limiting concentrations. Then the expressions of the activity coefficients of the two solutes were derived, which satisfy the condition of state function through the equality of the cross partial derivatives. Finally, such expressions were applied to the systems water(1)-NaCl(2)-sucrose(3) and water(1)-tetrabutylammonium bromide(2)-urea(3), verifying the accuracy of the proposed method.