Compressibilities of aqueous tert-butanol in the water-rich region at 25°C: Partial molar fluctuations and mixing schemes

Abstract

We measured the speeds of sound, u, and the densities, d, and, hence, determined the adiabatic compressibilities, κ_S, of aqueous tert-butanol (TBA) at small increments in mole fraction of TBA, x_TBA. Existing data for heat capacity, C_p, and thermal expansivity, α_p, were used to convert κ_S to the isothermal compressibilities, κ_T. Using these κ_T data, the normalized volume fluctuations, ^VΔ, and their composition derivative, the partial molar volume fluctuations of TBA, ^VΔ_TBA, (Y. Koga and P. Westh, Bull. Chem. Soc. Jpn., 1996, 69, 1505) were calculated. By using C_p data available in the literature we also calculated the normalized entropy fluctuations, ^SΔ, and the partial molar entropy fluctuations of TBA, ^SΔ_TBA. Furthermore, the density data at 15, 25 and 35°C in the literature were used to evaluate the thermal expansivities, α_p, from which the normalized cross (entropy–volume) fluctuations, ^SVΔ, and the partial molar cross-fluctuations of TBA, ^SVΔ_TBA, were calculated. The composition dependence of these fluctuation functions were interpreted in the light of the mixing schemes in aqueous solutions of TBA and other non-electrolytes and the transition between them (Y. Koga, J. Phys. Chem., 1996, 100, 5172).