Solute interactions in dilute aqueous solutions. Part 4.—Microcalorimetric study of ternary mixtures of urea and hydrophobic species

Abstract

Heats of dilution of urea, acetone, ethylmethyl ketone and tetrahydrofuran, and heats of mixing of urea with each of the other solutes have been measured at 25°C; the urea + acetone system was also studied at 5°C. The various enthalpic pair and triplet interaction coefficents, h_ij, h_ijj, etc. have been evaluated. The h_ii for the ketones and THF are positive and show a dependence on the alkyl chain length typical of the hydrophobic pair interaction, while for urea h_ii is negative. The cross coefficients h_ij are small, but positive. The triplet coefficients are generally small and of variable sign. At 5°C, all the coefficients are of a greater magnitude. The results are discussed in terms of various models for aqueous solutions of urea.