Degree Name

Master of Science (MS)

Semester of Degree Completion

1986

Thesis Director

David W. Ebdon

Abstract

A system of equations for fitting the experimental activity and osmotic coefficients of single and mixed electrolytes in aqueous solutions has been empirically developed in the present research. The results obtained through the equations developed here are comparable to the Pitzer equations in terms of accuracy and range of fitting. The equation for activity coefficient developed in the present research compared to the Pitzer activity coefficient equation has a form which is conveinient for computational purposes. The equation for activity coefficients is ln g = -╎ZmZx╎AD[I1/2/(1 + bI1/2)] + E I ln(I) + J1I + J2I3/2 where, b is fixed parameter having a value of 1.8; E, J1, and J2 are floating parameters. The corresponding equation for osmotic coefficients is obtained through the Gibbs-Duhem equation. The parameters have been evaluated by a nonlinear least squares computer program. This program weights all the data points equally. Parameters for both the coefficients are presented. In most of the cases data recommended by Robinson and Stokes is used. In the case of the 2-2 electrolytes one additional parameter is included to obtain acceptable results instead of two by Pitzer. Representing the 2-2 electrolytes in this manner ignores association constants, and thereby simplifying the treatment of these electrolytes at higher solution concentrations. Treatment of mixed electrolytes involves, in addition to pure electrolyte terms, parameters to account for the mixing effects is utilised. Only a few mixed electrolytes involving osmotic coefficients as experimental data has been treated here, and the results obtained are comparable to Pitzer's.

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