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.