Correlation of the Volumetric Properties of Uni-Univalent Electrolytes in Methanol–Water Mixed Solvent Media: A Pitzer Ion-Interaction Approach

Abstract

Although for a long time considerable attention has been paid to correlating the apparent molar volumes of electrolytes using the Pitzer ion-interaction approach in aqueous solutions, no attempt has, so far, been made to describe the volumetric data of electrolytes in mixed solvent media. This is due to the lack of experimental data on the pressure dependence of the dielectric constant in mixed solvent media. These data are essential to obtain the Debye–Hückel limiting law slopes for volumes that, in turn, are required to analyze the apparent molar volume vs. molality data of electrolytes in the light of the Pitzer ion-interaction approach. Here, we develop a convenient method which helped correlate the apparent molar volumes of electrolytes and estimate the Pitzer ion-interaction parameters for volume along with the Debye–Hückel limiting law slope for volumes. In particular, we have applied this approach to the literature apparent molar volume data of a number of uni-univalent electrolytes (viz., lithium chloride, sodium chloride, potassium chloride, sodium bromide, potassium bromide, sodium iodide, and potassium iodide) in methanol–water mixed solvent media at different temperatures. The parameters (namely, the apparent molar volume of the electrolyte at infinite dilution, $V_{{\phi {\text{,MX}}}}^{\infty }$, the second virial coefficient $B_{{{\text{MX}}}}^{V}$, and the third virial coefficient, $C_{{{\text{MX}}}}^{V}$) obtained here satisfactorily describe the molality dependence of apparent molar volumes of the investigated electrolyte solutions. The present correlation indicates that the electrolytes exist essentially as free ions in methanol–water mixed solvent media in conformity with what inferred earlier from conductivity measurements.