Thermodynamics of Ion Association in the Saturated Solution of The Mixed Solvent (methanol+water) and Ion Pairing at 25.0°C

In this study, the ion association phenomenon in the saturated solution of KCl in the mixed solvent (methanol+water) was studied. The solubility of this compound in the mixed solvent (methanol+ water by value percent of methanol = 60%), and in the presence of various molarities of NaNO3 was determined by the solvent evaporation method at 25.0°C. The results enable us to estimate the value of thermodynamic solubility product, Ksp(th), of KCl in the mixed solvent upon the extrapolation method (Ksp(th) = 0.1356). Although the model solubility product, Ksp(m), was calculated upon the semi theoretical semi experimental Debey-Huckle theory shows (Ksp(m) = 0.2308 ). Comparing the values of Ksp(th) and Ksp(m) with the concentration solubility product, (Ksp(c) = 0.5537), we can see that the differences are noticeable. We assume that, part of the differences comes from non-ideality and the other part from ion association phenomenon.