Definition of Hydration Parameters in the Region of Maximal Solvent Density

The approach to the definition of hydration numbers using the ultraacoustic method is critically discussed. Leaning upon a correct thermodynamic analysis, limited validity is shown of the main equation used in the publication of Onori over a wide range of state parameters. It is revealed that the mentioned equation is true only in the region of maximum solvent density. For this range of conditions, hydration numbers, the compressibility of hydration formations, molar volume and compressibility of water in hydration shells, molar volume and compressibility of stoichiometric mixtures of ions of NaCl are calculated based upon the experimental data of density and speed of ultrasound in solutions.