Interdiffusion of acids and bases•HCl and NaOH in aqueous solution

Abstract

Stokes magnetically stirred diaphragm cells have been used to measure interdiffusion of hydrochloric acid and sodium hydroxide in aqueous solution at 25 °C. Expressions are developed to estimate ternary diffusion coefficients for these mixtures. The analysis reveals sharp discontinuities between the diffusion properties of HCl-rich and NaOH-rich mixtures. Although the diffusion coefficients are sensitive to concentration, accurate analytic approximations for rates of interdiffusion can be obtained by averaging coefficients along the diffusion path. When HCl and NaOH interdiffuse, proton-coupled and hydroxide-coupled diffusion operating simultaneously on opposite sides of the diffusion boundary lead to rapid diffusion of inert Na+ and Cl− species.