Nonlinear Contribution of Hydrophobic Hydration in Osmotic Coefficients of Electrolyte Solutions

The osmotic coefficients of aqueous electrolyte solutions containing hydrophobic and hydrophilic ions is known since 1942, exhibit a nonlinear dependences on concentration. On the basis of the cluster representations proposed model solution which takes into account the hydration of the cation and anion of the electrolyte separately. Empirical parameters of the model equations are the hydration numbers and the dispersion of their distribution over the stoichiometric coefficients. The model is used to describe data on the osmotic coefficients of aqueous solutions of sodium carboxylates and tetrabutylammonium chloride and to calculate the mean ionic activity coefficients of salts. The numbers hydrophobic hydration of ions, as shown, nonlinearly dependent on electrolyte concentration. Concluded that extreme osmotic coefficients depending on the concentration due to differences of behavior hydration numbers of hydrophilic and hydrophobic ions.