Thermodynamics of the solubility of potassium nitrate in the mixed solvent, Ethanol+Water, and the related Ion-association

Using the evaporating method, the solubility of potassium Nitrate was determined in various mixtures containing Water and Ethanol at 25°C. The results show that the solubility of KNo3 decreases with increasing the mass percent of Ethanol in the mixtures. This trend is along with decreasing the dielectric constant of Water+Ethanol mixtures. Moreover, it can be concluded that the totqal solubility of KNO3 may be regarded as the sum of two contributions; one referring to the free ions in the solution and the other to K+NO3-ion-pairs which are formed in the saturated solution. Estimating the formation constant, KAm for the reaction K+(soln) + NO3-(soln) AK+NO3- (ion-pair) , upon Bjerrum or fuoss models, then it is quite easy to evaluate the contributions of free ions and K+NO3-(ion-pair) to the total solubility.