Effect of Salts on the Diffusion of Dissolved Non-electrolytes

Abstract

Experimental measurements of the diffusion coefficient Dlm of non-electrolytes in electrolyte solutions arc reported at 25°C. The systems studied are methane in aqueous NaCl, NaBr, Nai, CaCl2 and LaCl3, neopentane in NaCl and CaCl2, and benzene in (Me)4NBr, (Et)4NBr and (n-Bu)4NBr solutions. In all cases, Z>im was reduced by the addition of the salt. This decrease became greater as the ionic charge and ionic radius increased for a given ionic concentration. The fractional decrease in £>lm was greater for neopentane than for methane. Experimental results are compared with the multicomponent rigid sphere kinetic theory. The model is able to account for qualitative trends in the behaviour of Dlm for all of the systems except those involving tetra-alkyl-ammonium salts; the failure for these latter systems suggests that strong attractive forces are present, and that these forces have a pronounced influence on the collision dynamics.