Ternary mutual diffusion coefficients and densities of the system {z1NaCl +(1 –z1)Na2SO4}(aq) at 298.15 K and a total molarity of 0.5000 mol dm–3

Abstract

Isothermal ternary mutual diffusion coefficients (interdiffusion coefficients) have been measured for the system {z1NaCl +(1 –z1)Na2SO4}(aq) at a constant total molarity of 0.5000 mol dm–3 and 298.15 K using either Rayleigh or Gouy interferometry. Measurements were performed at NaCl molarity fractions of z1= 1, 0.90, 0.75, 0.50, 0.25 and 0. Densities of all solutions used in the diffusion experiments were measured using pycnometers and/or a vibrating densimeter. Trace diffusion coefficients have been evaluated from these results for the Cl–(aq) ion in 0.5 mol dm–3 Na2SO4(aq) and for the SO42–(aq) ion in 0.5 mol dm–3 NaCl(aq). The resulting values are D*(Cl–)=(1.681 ± 0.002)× 10–9 m2 s–1 and D*(SO42–)=(0.900 ± 0.006)× 10–9 m2 s–1, respectively. At all compositions, (D21)v, the cross-term diffusion coefficient of Na2SO4 due to a concentration gradient of NaCl, was found to be negative, whereas (D12)v, the cross-term diffusion coefficient of NaCl due to a concentration gradient of Na2SO4, was found to be positive.