THE TERNARY-SYSTEM WATER + 1-PROPANOL + UREA AT 298.15K ACTIVITY-COEFFICIENTS, PARTIAL MOLAL VOLUMES AND KIRKWOOD-BUFF INTEGRALS

The activity coefficiens, gamma-i, 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. gamma-1 and gamma-2 are found very little dependent on urea mole fraction x3, indicating the scarce influence of urea on the interaction free energy between water and propanol. V1 and V2 too are little dependent on urea concentration; V2 shows a characteristic minimum in dilute alcohol solution even at high x3 values. The increase of V3 with x3, a characteristic of hydrophilic compounds in water, is found even at high x2. The observed increase of the three homologous G(ii)'s and of G12 and the decrease of G23 and G12 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 G22 with urea addition may be due to the abduction of water molecules from the solvation sphere of propanol.