Transference number and solvation studies in tetramethylurea

Abstract

Transference numbers of sodium and potassium thiocyanate, have been measured in tetramethylurea at 25°C by a modified Hittorf's method in the concentration range 1.5-9.4×10^-2 M. A linear relationship is observed between the cation transference number and the square root of the concentration. Combining the limiting transference numbers and limiting equivalent conductances of these two salts, ionic mobilities of sodium, potassium, and thiocyanate ions have been found to be 16.08, 15.73, and 33.04 ohm^-1 cm² mol^-1, respectively. From these values ionic mobilities of other univalent ions, effective ionic radii, and solvatlon numbers have been computed. Higher solvation of cations than of anions of comparable sizes is consistent with the aprotic nature of the solvent.