Viscosities of solutions of electrolytes and non-electrolytes in ethylene carbonate at 40°C

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, η_r=17#x002B;A _η c ^1/2+B _η C+D _η c ².The pattern of the B_η coefficients is strikingly similar to that previously observed in the high dielectric constant, linear-chain hydrogen-bonded solvent, N-methylacetamide (NMA). Ionic values for φ_v and B_η have been obtained using a variety of splitting techniques. Alkali metal ions have large B_η coefficients indicating strong cation solvation with the ‘normal’ order Li>Na>K>Cs. Small anions have positive but much smaller B_η 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 _η=2.5φ_v, uniquely characteristic in H₂O of hydrophobic interaction. The two non-electrolytes have negative B_η 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_η coefficients are roughly linear in the square of B_η suggesting that they arise from hydrodynamic origins.