Speeds of sound and isothermal compressibilities in the water-rich region of aqueous 2-butoxyethanol and 2-butanone at 25 degrees C

Speeds of sound were measured at 25 degrees C in the water-rich region of aqueous 2-butoxyethanol (BE) and 2-butanone (BUT). Density, heat capacity, and thermal expansivity data available in literature were used to calculate isothermal compressibilities, kappa(T). The composition derivative, N(partial derivative kappa(T)/partial derivative n(B)), a third derivative of Gibbs free energy, showed a peak anomaly at x(BE) = 0.0175 for BE-H2O, and bend at x(BUT) = 0.033 for BUT-H2O. n(B) (n(BE) or n(BUT)) is the amount of the solute and x(BE) and x(BUT) are the respective mole fractions. The location of these anomalies were the same as those of other third derivatives found earlier for the same aqueous solutions. These anomalies were shown earlier to mark the transition point across which the mixing scheme changes in a qualitative fashion.