مطالعه ترموديناميكي تجمع يوني در محلول سير شده پتاسيم نيترات

Thermodynamic Study of Ion Association in Saturated Aqueous Solution of KNO3at250C

Introduction: Studies of aqueous electrolyte solutions almost always require consideration of non-ideality and ion-association. For many decades ion-association in electrolyte solutions has been an area of active research interest . A strong electrolyte solution deviate, partly by non-ideality and partly by ion- association from ideality. The non- ideality contribution could be evaluated by activity coefficients which can be estimated upon some theoretical models .The ion-association contribution, in turn, can be studied both theoretically and experimentally. Aim: Solubility of KNO3 in water at 25°C was determined. Upon choosing a suitable model for estimating the activity coefficient and using the iteration calculations,we estimate the ion association contribution to the solubility of considered ionic compound in the considered solvent and desired temperature. Materials and Methods:Potassium Nitrate was purchased from Merck Company and used without further purification. The saturated solution of Potassium Nitrate in deionized water was prepared at 25.0oC, and then the solubility of this salt in water was determined using Solvent Evaporating and Atomic Emission Spectrophotometric. Results:Comparison of the value of thermodynamic solubility product constant, Ksp(th), (Ksp(th) =exp(-AGdiss /RT) of KNO3 and the value of solubility product constant, 1 2 2 K sp ,obtained from this work showed a great diference (K sp =s f± , where s represents the solubility of KNO 3 in molL -1 and f± is the mean activity coefficient of KNO3 in saturated aqueous solution at 25°C upon Van Rysselberghe and Eisenberg model). Conclution: The difference between thermodynamic solubility product constant, Ksp(th), of KNO3 and the solubility product constant, K^p, can be satisfactorily explained using a combination of Van Rysselberghe - Eisenberg model for estimating f ± and Ion- Association theories.