Hydrophilic and hydrophobic phenomena in electrolyte solutions

The hydration parameter values of alkali-metal chlorides, bromides, iodides and nitrates at 25 °C have been studied from the extrapolation of activity coefficient data. The ion-size parameter å used in the simplified form of the Stokes and Robinson equation is chosen as the sum of Marcus's aqueous ionic radii of the cation and anion of the electrolyte. Values of activity coefficients are taken from Robinson and Stokes. Caesium chloride, caesium bromide, caesium iodide, potassium nitrate, rubidium nitrate and caesium nitrate show negative hydration, while other salts show positive hydration.