Thermodynamic study of ion- association in KNO3 solution in the mixed solvent (water +methanol)

The solubility of KNO3 in the mixed solvent (water 85%+methanol 15%) were determined by using solvent evaporating method at different temperatures (25, 30, 40, 50, 60 ;C). In addition the equilibrium constant of ion pair formation, KIP, for K+NO3 – ion-pair on the basis of Fuoss contact ion pair model was calculated. Upon choosing the extended Debye-Hückel model for estimating the mean activity coefficient of ions in the saturated solution and using the itteration calculations, we estimated the ion association contribution to the solubility of considered ionic compound in the mixed solvent at various temperatures. The value of thermodynamic solubility product constant, Ksp (th), BHdiss, BSdiss and BGdiss of KNO3 in the mixed solvent (water 85%+methanol 15%) was calculated.