ACTIVITY COEFFICIENTS FOR 2 TERNARY SYSTEMS - WATER-UREA-TETRAMETHYLAMMONIUM BROMIDE AND WATER-UREA-TETRABUTYLAMMONIUM BROMIDE AT 2K DEGREES

Isopiestic vapor pressure measurements have been made for two ternary systems, H2O-urea-Me4NBr and H2O-urea-Bu4NBr at 25°. A method similar to that employed by Bower and Robinson was used for evaluating the activity coefficients of urea and salts. In the concentration range studied, it was found that each solute component is salted in" by the other as shown by the considerable lowering of the activity coefficients in the presence of the other solute. The "salting-in" effect was found to increase greatly with the cationic size of the tetraalkylammonium salt. The lowering of the activity coefficients of urea and Bu4NBr found in this study may be due either to the water-structure breaking effect of urea or to the formation of some complex-like aggregates between urea and the tetraalkylammonium salt in aqueous solutions. The free energies of transfer of tetraalkylammonium bromides from water to urea solutions have been calculated. The results indicate that the transfer can proceed spontaneously from water to urea solution."