Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

Osmotic coefficients were measured by the vapor pressure osmometry technique for dilute aqueous solutions of Me4NBr, Et4NBr, Pr4NBr, Bu4NBr, Me4NCl, and Me4NI at 308.15 K. From the experimental osmotic coefficient data, the water activity, water activity coefficient and vapor pressure values were evaluated. The experimental osmotic coefficient data were fitted to the Pitzer equation from which the values of the mean molal activity coefficients were calculated. The values of the obtained osmotic and mean molal activity coefficient data for the bromides decreased with the size of the cation: Bu4N+ less than Pr4N+ less than Et4N+ less than Me4N+. The results for the tetramethylammoniums show that the osmotic and mean molal activity coefficient varies in the following way: Me4NCl greater than Me4NBr greater than Me4NI. However the values of the water activity, vapor pressure depression, and the water activity coefficient data follow the order Me4NBr less than Et4NBr less than Pr4NBr less than Bu4NBr and Me4NCl less than Me4NBr less than Me4NI, which implies that the smaller ions hydrate more water molecules than the ions with larger size.