The ternary system water + 1-propanol + urea AT 298.15K. Activity coefficients, partial molal volumes and kirkwood-buff integrals.

Abstract

The activity coefficiens, γi, and the partial molal volumes, V i, of the three components of the ternary system water(1)+1-propanol(2)+urea(3) have been measured at 298.15 K in the entire domain of full miscibility. These data have been used to calculate the six Kirkwood-Buff (K-B) integrals, G ij, of the ternary mixture. γ 1 and γ 2 are found very little dependent on urea mole fraction x 3. indicating the scarce influence of urea on the interaction free energy between water and propanol. V 1 and V 2 too are little dependent on urea concentration; V 2 shows a characteristic minimum in dilute alcohol solution even at high x 3 values. The increase of V 3 with x 3, a characteristic of hydrophilic compounds in water, is found even at high x 2. The observed increase of the three homologous G ii's and of G 12 and the decrease of G 23 and G 12 with addition of urea indicate that this compound brings about an enhanced homocoordination of the three components, as well as an increase of the urea-water affinity, and suggest that the observed increase of G 22 with urea addition may be due to the abduction of water molecules from the solvation sphere of propanol.