Kresheck, Gordon C.||Graham, John D. (Professor of chemistry)||Albers, Robert J.
M.S. (Master of Science)
Department of Chemistry
Changes in partial molar volume are known to accompany the formation of micelles and also the transfer of nonpolar gases from aqueous to nonpolar solvents. The structure of water is thought to be important in these processes. Since considerable evidence suggests that urea may disrupt water structure, it was of interest to determine its effect on the partial molar volume of model compounds containing nonpolar side chains. In this study the partial molal volumes of a homologous series of aliphatic alcohols, carboxylic acids, acid salts, and amino acids were determined at infinite dilution in 6M urea and compared to the known partial molal volumes (also at infinite dilution) in water. The results indicated that for the transfer of the nonpolar side chain from water to 6M urea at 25° is positive for all solutes studied. Definite head group effects were also noted for each of the different classes of solutes. The effect of urea on the hydrocarbon portion was interpreted on the basis of five parameters, AV°t, Ks (salting out coefficient), AFT. AHt, and Ast; all of which suggest that urea is disrupting the water structure which results in enhanced solvation of the hydrocarbon. It was shown that the Drude-Nernst equation could be used for charged solutes to qualitatively predict the volume change on transfer from water to 6M urea or pure ethanol. This prediction depends upon the dielectric constant of the solvent. It was further shown that the volume change for the aliphatic acids was associated with the difference in conductivity of these solutes in water and urea. Solvation differences based upon heat capacity data also seem to be a factor in interpreting the observed volume changes for the acids and salts. All of these considerations are thought to be associated with the alteration of the water structure by the addition of urea.
Hargraves, Walter A., "Effect of aqueous urea solutions on the partial molar volume of aliphatic acids, acid salts, amino acids, and alcohols" (1969). Graduate Research Theses & Dissertations. 2720.
ix, 102 pages
Northern Illinois University
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