DETERMINATION OF THE DIFFUSION-COEFFICIENT OF THE GREEN AND VIOLET ISOMERS OF CR-2(SO4)(3) IN AQUEOUS-SOLUTION

The diffusion coefficients of the green and violet isomers of Cr-2(SO4 )(3) in water and acidic solutions were measured at 298 K by using a d iaphragm-cell method. These data were determined as a function of conc entration of solute, and analyzed in terms of the diffusion potential gradient and changes in the mean activity coefficient and viscosity. T he diffusion coefficients of violet Cr-2(SO4)(3) are larger than those of green Cr-2(SO4)(3) at the same molar concentration, and the two se ts of D values demonstrate different concentration dependencies. The r esults can be understood in terms of the mean activity coefficient of Cr-2(SO4)(3), which is of larger magnitude for violet Cr-2(SO4)(3) sol ution and is more dependent on salt concentration. The presence of H2S O4 in large amounts, for example 2 kmol m(-3), is found to decrease bo th the green and violet Cr-2(SO4)(3) diffusion coefficients. At lower concentrations of acid, there is a slight increase in D values. The ef fect of acid is to modify the diffusion potential, as well as the mean activity coefficients of Cr-2(SO4)(3) and the viscosity of solution. Finally, compared with other metal sulphate systems previously investi gated, both the green and violet isomers of Cr-2(SO4)(3) exhibit small er diffusion coefficients than those of the 2-2 electrolytes (Cu, Ni, Zn) and Fe-2(SO4)(3).