Thermochimica Actu, 87 (1985) 225-229 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands 225 zyxwvutsrqp SOLUBILITY OF 1: 1 ELECTROLYTES IN 1,1,3,3-TETRAMETHYL- UREA-WATER MIXTURES DOW M. MAHARAJH, ANTHONY GUISEPPI-ELIE and RAMSUMAIR SOOKRAM zyxwvutsrqpon Department of Chemistry, The University of the W est Indies, St. Augustine, Trinidad (W est Indies) (Received 20 November 1984) ABSTRACT The solubilities of five 1: 1 electrolytes in 1,1,3,3-tetramethylurea (TMU)-water mixtures have been determined. Combination of these data and ion pair association for the electrolytes in TMU-water mixtures yield solubility (ion-activity) products from which free energies of solution of the ionic species M+ + X- have been calculated. Using the corresponding data in water, the free energies of transfer of M+ +Y - from water to TMU-water mixtures are obtained. The changes in free energy that accompany the transfer of electrolytes from water to mixed aqueous solvents will be discussed. INTRODUCTION Several papers [l-3] from our laboratory have been concerned with the effect of water on tetramethylurea. As a continuation of these investigations, the present paper reports the solubilities of the alkali halides in the various mixtures of water and tetramethylurea. In spite of the practical interest of 1,1,3,3-tetramethylurea (TMU), little information is found in the literature regarding the solubilities of 1: 1 electrolytes in this solvent and its aqueous solutions. The aim of the present study is to measure the solubilities of 1: 1 electrolytes in TMU-water mixtures in order to derive the free energies of transfer of these electrolytes from water to the TMU mixtures. EXPERIMENTAL The alkali-metal halides were AR grade reagents. The solvent TMU was purified as described elsewhere [l]. Triply distilled, conductivity water was used in the preparation of all mixtures. Blank determinations for chloride were done on each batch of water used in the preparation of the mixtures. Saturated solutions were obtained by adding an excess amount of the salt 0040-6031/85/$03.30 0 1985 Elsevier Science Publishers B.V.