The diffusion of monocarboxylic acids in aqueous solution at 25°

Abstract

The diffusion of the monocarboxylic acids formic, propionic, and n-butyric in aqueous solution at 25° over the range 0.06-2.00M is studied by the Gouy interferometric method. The results, together with Vitagliano's and Lyons's results for acetic acid, are corrected to allow for the effects of ionization. A treatment of the effects of molecular association on the experimental diffusion coefficients is proposed, and applied with moderate success to acetic acid, propionic acid, and n-butyric acid. Mobilities of the undissociated acid molecules at infinite dilution are found to be greater than the limiting mobilities of the corresponding anions. Association constants of the monocarboxylic acids over the concentration range studied are calculated from existing activity data.