DIAPHRAGM DIFFUSION CELL - A CLOSED FORM SOLUTION TO THE TRANSPORT-EQUATION AND ITS APPLICATION TO THE DETERMINATION OF THE CONCENTRATION-DEPENDENCE OF THE HCL-H2O INTERDIFFUSION COEFFICIENT

In a thermodynamically non-ideal solution, the interdiffusion coefficient D(c) of a two-component system is a function of the concentration c. Since the mean concentration cBAR in a diaphragm cell remains constant during interdiffusion, we have found it useful to expand D(c) in a Taylor series about cBAR. After truncating the series and substituting the result into the diaphragm cell transport equation, we obtain a Bernoulli ordinary differential equation, which we solve in closed form. This solution is experimentally tested by determining D(c) from diaphragm cell data which we accumulated on aqueous hydrochloric acid at 25-degrees-C. Our results are in qualitative agreement with those of R. H. Stokes, who obtained D(c) from diaphragm cell data by using a graphical method [J. Am. Chem. Soc. 72, 2243 (1950)].