Viscosities Of Solutions Of Electrolytes And Nonelectrolytes In N-Methylacetamide At 35° And 55°C

Document Type

Article

Publication Date

12-1-1980

Published In

Journal Of Solution Chemistry

Abstract

The viscosities of dilute solutions of a number of tetraalkylammonium and alkali metal halides, tetraphenylarsonium chloride, sodium tetraphenylborate, and tetrabutylammonium tetrabutylborate, as well as several nonelectrolytes have been measured in the high dielectric constant solvent N-methylacetamide (NMA) at 35 and 55°C. The relative viscosities were fitted to the extended Jones-Dole equation, ηГ = 1 + AηC^(¹⁄₂) + BηC + DηC². The pattern of behavior of the Bη coefficients is roughly similar to that observed in H₂O. However, the small ions have exceptionally large Bη values in this solvent due to strong solvation effects, while the large organic ions do not display the sharp crossing of the Einstein law, Bη=2.5 φV, characteristic in H2O of hydrophobic interaction. The Dη coefficients roughly parallel the Bη behavior and display remarkably regular ionic trends. This suggests that they arise largely from hydrodynamic origins. Nonelectrolytes have small or negative Bη coefficients showing that the Einstein law is not applicable at the molecular level and that nonelectrolytes are poor models for structurally similar ions. A simple mixture law is presented as an alternative to the Einstein law to explain the Bη coefficients.

Keywords

Viscosity, electrolyte, nonelectrolyte, alkali metal halide, tetraalkylammonium ions, solvation jones and Dole equation, nonaqueous solvent, N-methylacetamide

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