| Abstract
| - Isothermal mutual diffusion coefficients (interdiffusion coefficients) were measured for ternary aqueousmixtures of NaCl and Na2SO4 at a constant total molarity of 1.500 mol·dm-3 at 298.15 K, using Rayleighinterferometry with computerized data acquisition. The experiments were performed at NaCl molarityfractions of z1 = 1, 0.90, 0.75, 0.50, 0.25, and 0. These measurements supplement our earlier results attotal molarities of 0.500 and 1.000 mol·dm-3. Diffusion coefficients were also measured at three additionalconcentrations of Na2SO4(aq). Densities of all solutions were measured with a vibrating tube densimeter.At all ternary solution compositions, one cross-term diffusion coefficient has small negative values whereasthe other has larger positive values. Comparing the results at 0.500, 1.000, and 1.500 mol·dm-3 showsthat both main-term diffusion coefficients decrease with increasing total concentration at any fixed valueof z1, whereas both cross-term coefficients are shifted in a positive direction. At 1.500 mol·dm-3 both theNaCl main-term and cross-term diffusion coefficients have a maximum as a function of z1, whereas theNa2SO4 cross-term coefficient has a minimum. Trace diffusion coefficients D*(Cl-) = (1.145 ± 0.02) ×10-9 m2·s-1 and D*(SO42-) = (0.805 ± 0.015) × 10-9 m2·s-1 were extrapolated from these results for theCl-(aq) ion in 1.500 mol·dm-3 Na2SO4(aq) and for the SO42-(aq) ion in 1.500 mol·dm-3 NaCl(aq). Valuesof D*(Cl-) in Na2SO4(aq) and in NaCl(aq) were found to be essentially identical, as were D*(SO42-) inthese same two electrolytes, provided the comparisons are made at the same volumetric ionic strengths.
|
