Chronopotentiometric diffusion coefficients have been measured for Ag+, Tl+, and Cd2+ ions in molten calcium nitrate tetrahydrate over the temperature interval 15-60°. The diffusion coefficients, which are in the range 10-8 to 10-6 cm2/sec, all show non-Arrhenius temperature dependences. Despite the differences in charge and size, the Arrhenius coefficients of the diffusivities at equal temperatures are almost the same for all ions and are also very close to those previously observed for electrical conductance and shear and bulk fluidities of the pure solvent. The cooperative character of the basic mass-transporting event is thus further supported. At a given temperature, DAg+ and DTI+ are about twice as large as DCd2+. Application to these data of an empirical, Stokes-Einstein type of correlation between diffusivity and fluidity for fused nitrates suggests that for DCd2+ the mobile entity is the hydrated cation Cd(H2O)42+.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry