Thermodynamics of aqueous and water-organic solutions of electrolytes from very dilute to saturated concentrations

Abstract

The solutions of electrolytes in water such as NaCl in H 2O are treated as a binary system of NaClH 2O. Only at very low concentrations does dissociation into Na + and Cl − becomes significant. This is similar to copper, where only a small fraction of the electrons participate in electronic conduction. The Hoch-Arpshofen model is applied to calculate the activity coefficient Tin Y of NaCl and other electrolyes in water. At high concentrations the interaction parameter is W 2, (NaCl), W is the interaction energy, 2 is the size of the complex, and (NaCl) is the molecule with the mole fraction x in our model. A solution with a complex size of 2 is a regular solution. At very low concentrations, x, NaCl (mole fraction) < 0.01, another term W m, (H2O) is required, with m = 200 or higher. In this case we have a complex made up of 199 molecules of water and one molecule of NaCl, indicating dissociation of NaCl into Na + and Cl −. The application of this approach is supported by the fact that the activity coefficient of HCl in organic-water solutions deviates at lower and lower concentrations from the regular solution approach, as the organic concentration increases. This approach also calculates the activity coefficient of water. Because the salts are not completely miscible with water, a constant is added, to set the activity to one, when the solubility limit is reached. In treating ternary and larger solutions, such as CaCl 2KClNaClH 2O the interaction between CaCl 2 and NaCl etc is calculated from the binary CaCl 2NaCl phase diagram.