Osmotic and activity coefficient studies on the aqueous solutions of tetramethylurea at 298.15 K

Abstract

The osmotic coefficients and densities of good precision of aqueous solutions of tetramethylurea (TMU) in the concentration range 0.1 to 8.0 <i>m</i> at 298.15 K have been experimentally determined and the data used to calculate apparent

and partial molar volumes, activities and activity coefficients of water and TMU as a function of concentration of TMU. It has been observed that partial molar volumes of solvent and solute go through a maximum and a minimum, respecti vely, at about 0.055 mole fraction of TMU. The activity coefficient values for H₂O increase, while those of TMU decrease with increase in concentration of TMU. These results arc compared with those of aqueous urea solutions and are in agreement with literature values indicating the presence of hydrophobic interactions in H₂O -TMU solutions. Excess free energy of mixing of TMU in water has been calculated using activity data at 298.15 K and is found to decrease as a function of TMU concentration in the studied concentration range. The values for the attractive and repulsive contributions to the solute solvent interaction have been estimated and data is compared with other non-electrolytes. Further, applying McMillan-Mayer theory of solutions to the data, osmotic second and third virial coefficients for TMU have been obtained. The values of virial coefficients, on decomposition into attractive and repulsive contributions to solute-solute interactions, indicate that pairwise interaction between TMU molecules and water structure making effect is more prominent than triplet and higher order interactions in the studied concentration range of aqueous-TMU solutions.