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

Document Type : Research Paper




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.