Phase diagrams and liquid−liquid equilibrium (LLE) data of the aqueous poly(ethylene glycol) (PEG) + sodium tungstate two-phase system have been determined experimentally at (298.15, 303.15, 308.15, 313.15, and 318.15) K. The effects of temperature on the binodal curves and tie-lines have been studied. It was found that an increase in temperature caused the expansion of the two-phase region. It was also found that the concentration of salt which is in equilibrium with a certain concentration of PEG decreases by increasing temperature. The effect of temperature on the phase-forming ability in the investigated system has been studied based on a salting-out coefficient obtained from fitting the binodal data to a Setschenow-type equation for each temperature. On the basis of cloud point values, the energetics of the clouding process have been estimated, and it was found that entropy increase is the driving force for biphasic formation.
Osmotic coefficients were measured by the vapor pressure osmometry technique for dilute aqueous solutions of Me 4 NBr, Et 4 NBr, Pr 4 NBr, Bu 4 NBr, Me 4 NCl, and Me 4 NI 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: Bu 4 N + < Pr 4 N + < Et 4 N + < Me 4 N + . The results for the tetramethylammoniums show that the osmotic and mean molal activity coefficient varies in the following way: Me 4 NCl > Me 4 NBr > Me 4 NI. However the values of the water activity, vapor pressure depression, and the water activity coefficient data follow the order Me 4 NBr < Et 4 NBr < Pr 4 NBr < Bu 4 NBr and Me 4 NCl < Me 4 NBr < Me 4 NI, which implies that the smaller ions hydrate more water molecules than the ions with larger size.
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