Viscosities of solutions of electrolytes and non-electrolytes in ethylene carbonate at 40°C |
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Authors: | Peter T. Thompson Barbara Fisher Robert H. Wood |
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Affiliation: | (1) Department of Chemistry, Swarthmore College, 19081 Swarthmore, PA;(2) Department of Chemistry, University of Delaware, 19711 Newark, DE |
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Abstract: | The viscosities of dilute solutions of a number of tetraalkylammonium and alkali metal halides, tetraphenylarsonium chloride, sodium tetraphenylborate, tetrabutylammonium tetrabutylborate, water, and 3,3-diethylpentane have been measured in the high-dielectric constant solvent, ethylene carbonate (EC) at 40°C. Crude values of the apparent molar volumes of these solutes have also been obtained. Relative viscosities were fitted to the extended Jones-Dole equation, r=17#x002B;Ac1/2+BC+Dc2.The pattern of the B coefficients is strikingly similar to that previously observed in the high dielectric constant, linear-chain hydrogen-bonded solvent, N-methylacetamide (NMA). Ionic values for v and B have been obtained using a variety of splitting techniques. Alkali metal ions have large B coefficients indicating strong cation solvation with the normal order Li>Na>K>Cs. Small anions have positive but much smaller B values than in NMA. The observed order does suggest, however, a small degree of anion solvation. Large organic ions do not display the sharp crossing of the Einstein law,D=2.5v, uniquely characteristic in H2O of hydrophobic interaction. The two non-electrolytes have negative B coefficients showing that the Einstein law is not valid at the molecular level and that hydrocarbons are not good models for their isoelectronic tetraalkylammonium ion counterparts. An empirical modification of the Einstein law to account for the finite size of the solvent molecules is discussed. As in NMA the D coefficients are roughly linear in the square of B suggesting that they arise from hydrodynamic origins. |
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Keywords: | Ethylene carbonate viscosity Jones-Dole equation nonaqueous solvent solvation tetraalkylammonium ions alkali metal halides electrolytes non-electrolytes partial molal volumes high dielectric constant solvents |
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