VAPOR-PRESSURES OF AQUEOUS 2-BUTOXYETHANOL SOLUTIONS AT 25-DEGREES-C - TRANSITIONS IN MIXING SCHEME

The vapor pressures of aqueous solutions of 2-butoxyethanol (BE) were determined at 25.00-degrees-C. The partial pressures of BE and H2O and hence the excess partial molar free energies, G(m)E(i) (i = BE or H2O) were calculated by the Boissonnas method. Using the values of the excess partial molar enthalpies, H(m)E(i) (i = BE or H2O), measured previously in this laboratory (Can. J. Chem. 1989, 67, 671), the excess partial molar entropies, S(m)E(i) (i = BE or H2O), were calculated. From the concentration dependence of these excess partial molar quantities, more detailed insight into the mixing scheme became available. In particular, two boundaries were noted within the single-phase domain that separate the regions in which the thermodynamic properties and hence the mixing schemes are different. The transition in mixing scheme from the water-rich region to the intermediate region is associated with cusp or peak anomalies in the quantities that are proportional to the third derivatives of the free energy. The transition from the intermediate to the BE-rich region appears to be accompanied by jump anomalies of the fourth derivatives of the free energy.