Volumes and heat capacities of ternary aqueous systems at 25.degree.C. Mixtures of urea, tert-butyl alcohol, dimethylformamide, and water

Abstract

The densities and heat capacities per unit volume were measured for the systems urea (U)-/er/-butyl alcohol (TBA)water (W) and dimethylformamide (DMF)-TBA-W at 25 °C with a flow densimeter and a flow microcalorimeter. One of the nonaqueous components was kept at a constant low concentration and whenever possible the other component was varied over the whole mole fraction range. From these data, combined with previously published data on NaCl-U-W and on Bu4NBr-U-W, volumes and heat capacities of transfer were calculated and compared with the corresponding excess functions of the binary systems to get an overall view of these ternary systems. In the water-rich region the thermodynamic properties are characterized by strong solute-W and solute-solute interactions. At the nonaqueous end the thermodynamic properties are reflecting mostly solute-solvent interactions. Through an understanding of the two ends it becomes easier to account for the various inflection points, maxima or minima in the transfer functions.Mixed aqueous solvents are used intensively in chemistry, biology, and industry to control factors such as solubility, stability of systems, and kinetics of reactions. Despite numerous studies on thermodynamic, transport, and spectral properties,211 there is still disagreement on the nature of the interactions which are responsible for the characteristic trends in the composition dependence. For example, often maxima, minima, or inflection points are observed which are then in-terpreted in terms of various effects such as structural changes in the solvent, preferential hydration, or association complexes. However, depending on the property studied, these extrema or inflection points often do not occur at the same mole fraction and depend on the nature of the solute, making many of these interpretations dubious.Much of the confusion probably comes from the limited range of most studies. A better understanding of ternary

Thermodynamics of the salting effect; free energies, enthalpies, entropies, heat capacities, and volumes of the ternary systems electrolyte–alcohol–water at 25 °C

“…This explains why h,, has a sign different from AHoE(W + D) since this latter function is reflecting differences in solute-solvent interactions. A general discussion of these structural interactions is given elsewhere (18). The signs of all the pair parameters can be explained with this approach.…”

“…In the first instance standard enthalpies of transfer are calculated from the standard enthalpies of solution of the solute in the binary mixture and in pure water; For volumes and constant pressure heat capacities the parameters are given by the apparent molal quantities at low mN in the ternary and binary systems (17,18); Or the emf a using a ion glass The pair interaction parameters are related to cathode and a silver -silver halide anode as described in the usual way. Assuming cNE to be indePOintud (7).…”

Novel bile acid sequestrant: A biodegradable hydrogel based on amphiphilic allylamine copolymer

“…52 According to the structural hydration co-sphere model established by Desnoyer and his co-workers, the overall influence of the solute on the structure of water molecules is represented by a spherical shell and the concentration effect by the overlapping of two such co-spheres. [53][54][55] For the electrostatic interaction between hydrophilic protonated amino groups and carboxyl groups, the values of enthalpy (ǻH 1 ), entropy (ǻS 1 ) and free energy (ǻG 1 ) are negative. This spontaneous process was supported by enthalpy.…”

Interactions between cations and sugars. II. Enthalpies, heat capacities, and volumes of aqueous solutions of Ca2+–D-ribose and Ca2+–D-arabinose at 25 °C

“…Hence, the apparent molal volume of the sugar in water +VS is given by where Ms is the molecular weight of the sugar and p and po the densities (g ~m -~) of the solution of molality ms and of pure water, respectively. One may also define the apparent molal volume of the sugar S in a solution of electrolyte of molality mE by using the densities p(ms, m~) and p(mE) (15). At low ms concentrations, the transfer function +vs(ms, mi) -+vs(ms) may be assumed to be a standard value (infinite dilution) and we may write Similarly, by considering the transfer of the electrolyte from water to the sugar solutions we get…”