Volumetric and Viscometric Studies on an Aqueous Urea Solution

Abstract

Of late there has been a renewed inerest in the thermodynamics and other investigations on the behaviour of urea (denaturants) in aqueous solution which induce changes in structure and properties of proteins including their solubility, denaturation, dissociation into subunits and the activity of enzymes. With this in view, density and viscosity of aqueous urea solutions were determined as a function of concentration at 35, 40, 45, 50 and 55C, respectively. The apparent molal volume $(\\phi _v )$ of urea was found to be linear function of solute concentration. From the $\\phi _v$ versus molality ( m ) plot the apparent molal volume at infinite dilution, $\\phi _v^o$ (taken to be equal to partial molal volume, $\\bar V_2^o$ ) was determined. Viscosity coefficients B and D were calculated on the basis of the viscosity of the solutions and the solvent concerned using the Jones-Dole equation. The activation parameters for viscous flow $(\\Delta G^{\ e} , \\,\\Delta S^{\ e}\\ {\\rm and\\ }\\Delta H^{\ e} )$ were also calculated by means of the Eyring equation. The data were interpreted in terms of the structure making behaviour of urea in water at 35-55C temperature range.