Diffusion with hydrolysis equilibria: transport coefficients of aqueous SO 2 , NH 3 , and Na 2 CO 3

Abstract

Practical equations are derived for estimating diffusion coefficients and Onsager transport coefficients of aqueous solutes subject to hydrolysis. The derivation is based on the Nernst–Hartley method which is extended to include chemical reaction of solute with solvent. The derived equations and existing mobility data are used to estimate transport coefficients of aqueous SO 2 (20 °C), NH 3 (15 °C), and Na 2 CO 3 (25 °C). In dilute solution where hydrolysis is extensive, rates of diffusion of SO 2 and NH 3 are increased by about 50% and 25%, respectively, relative to unhydrolyzed solute. Because of the carbonate–bicarbonate equilibrium, diffusion in aqueous Na 2 CO 3 is a ternary process characterized by coupled transport of NaOH. In dilute solution the NaOH flux may exceed the flux of Na 2 CO 3 .