PARTIAL MOLAL VOLUME OF IONS IN VARIOUS SOLVENTS

The partial molal volumes of ions in the solvents methanol, water, and N-methylpropionamide (NMP) have been examined by using the Frank and Wen model for ion-solvent interactions. The partial molal volume of an ion is assumed to be due to three major components, V̄0(int), the intrinsic partial molal volume (equal to the crystal volume), V̄0(disord), the disordered partial molal volume (void space effects), and V̄0(elect), the electrostriction partial molal volume. The results of fitting the V̄0(ions) in these solvents to various semi-empirical equations indicate that V̄0(disord) is related to the structure of the solvent. This disordered effect may be visualized as the void space caused by the solvated ion rather than improper packing in the electrostricted region. The V̄0(elect) of the ions in the various solvents is proportional to 1/r (r = crystal radius) and in the predicted order V̄0(elect) of methanol > water > NMP).