Thermochemical investigations of associated solutions: calculation of solute--solvent equilibrium constants from solubility measurements.
A simple solution model that has lead to successful predictive equations for the partial molar excess properties of a solute in simple binary solvent mixtures containing only nonspecific interactions is extended to include association between the solute and one of the solvent components. An expression is derived and tested for its ability to describe anthracene solubilities in binary solvent mixtures containing benzene. The best description of the experimental solubilities requires the formation of a 1:1 anthracene-benzene complex, with a molarity-based equilibrium constant of KcAC approximately equal to 0.107 M-1. In comparison, a stoichiometric complexation model which attributes all solubility enhancement to the formation of anthracene-benzene complexes requires a somewhat larger equilibrium constant (KcAC approximately equal to 0.228 M-1) to describe the solubility behavior of anthracene in the benzene-n-heptane system. The results of these calculations illustrate that the determination of solute-solvent equilibrium constants from solubility data depends on the theoretical model used and the manner in which nonspecific interactions are incorporated into the model.
Thermochemical investigations of nearly idela binary solvents. II. Standard heats of solution in systems of nonspecific interactions
Standard heats of solution at 25°C are reported for squalane in mixtures ofn-heptane + iso-octane and in binary mixtures of chloroform, carbon tetrachloride, and cyclohexane; for cyclohexane in chloroform + carbon tetrachloride; and for chloroform in carbon tetrachloride + cyclohexane. General equations based on simple mixing models are developed for the excess thermodynamic properties of a solute at infinite dilution in a binary solvent. For the systems studied, mixing equations based on volume fractions give better agreement than those based on mole fractions, and the agreement is further improved by the use of weighting factors based on the properties of the solute + solvent binary systems.
Thermodynamics of aqueous solutions of nonelectrolytes. I. Enthalpies of transfer of 1-methyl-2-pyrrolidinone from water to aqueous methanol
Molar excess enthalpies were measured for 1-methyl-2-pyrrolidinone mixed with water and with methanol over the whole concentration range and with aqueous methanol at the low mole fraction of 1-methyl-2-pyrrolidinone at 298.15°K, using a LKB flow microcalorimeter. Enthalpies of transfer of 1-methyl-2-pyrrolidinone from water to aqueous methanol were estimated from the molar excess enthalpies. The result was qualitatively in agreement with the conclusion described by Arnett et al.