Mutual Diffusion Coefficients and Refractive Index Increments of K2SO4(aq) at 298.15 K from Rayleigh Interferometry

Abstract

Isothermal mutual diffusion coefficients (interdiffusion coefficients) were measured for K2SO4(aq) at 298.15 ± 0.005 K, at numerous concentrations ranging from dilute solutions to near saturation (0.59648 mol·dm–3; 0.61349 mol·kg–1) under free diffusion boundary conditions, using high precision Rayleigh interferometry. Under the experimental conditions these diffusion coefficients are on the volume-fixed reference frame Dv. Two series of experiments were performed, the first using the traditional experimental approach with a mercury lamp source and with the interference patterns being recorded on glass photographic plates, and the second with a He–Ne laser light source and computerized data acquisition using a photodiode array. The results from both series of experiments are in excellent agreement, and generally yield diffusion coefficients precise to at least 0.002 × 10–9 m2·s–1 (0.15% to 0.19%) and in most cases to 0.001 × 10–9 m2·s–1 (0.07% to 0.1%). These experiments also yield accurate values of the refractive index differences for the solution pairs used in the diffusion experiments. The new diffusion coefficients are compared to two sets of published values of diffusion coefficients for K2SO4(aq) which are somewhat discrepant from each other. This study extends and complements our earlier work on the diffusion coefficients of the most common brine salts: NaCl(aq), KCl(aq), MgCl2(aq), CaCl2(aq), Na2SO4(aq),]MgSO4(aq), NaHCO3(aq), and KHCO3(aq) at 298.15 K.