Thermodynamic properties of aqueous salt containing urea solutions

Urea and inorganic ions are present in some of the physiological systems, e.g. urine. Understanding the interactions in urea/salt/water is a preliminary step to shed light on more complicated behavior of multi-component physiological systems. State-of-the-art models as well as thermophysical properties can be applied to understand the interactions in these systems. In order to determine such interactions densities, mean ionic activity coefficients (MIACs), osmotic coefficients, and solubility were measured in aqueous solutions of urea and different salts. Densities were determined at temperatures 293.15, 303.15, and 313.15 K for urea concentrations up to 3 molal and up to 1 molal for NaCl. Osmotic coefficients and MIACs were obtained at 310.15 K by using the vapor-pressure osmometry and potentiometry methods, respectively. Ternary aqueous urea solutions containing NaCl, KCl, NaBr, KBr, LiBr, NaNO3, and LiNO3 at two different concentrations of urea (0.3 and 1 molal) as well as at three salt concentrations (0.25, 0.5, and 0.75 molal) were considered. Moreover, urea solubility was also measured at 310.15 K in 3 and 5 molal NaCl solutions in the present work. Experimental data obtained in this work showed that the salt primarily dictates the volumetric properties and the MIAC while the solute with higher concentration determines the behavior of osmotic coefficients in these solutions. The ePC-SAFT model (without any adjustable mixture parameter) was used to accurately predict the experimental densities, activity and osmotic coefficients, and solubilities of the studied mixtures.