Diffusion Coefficients for Copper (II) in Aqueous Cupric Sulfate‐Sulfuric Acid Solutions

Diffusion coefficients for Cu(II), , were determined at 25°C in over the concentration range . The reported values of represent average values for the physical properties over the diffusion layer, and for the diffusing Cu(II) species, which consist of Cu ++ ions and ion pairs. Thus, represents an effective value that is suitable for substitution into the various mass‐transfer equations derived by assuming constant properties. At low concentrations (0.4–6 m M ) static mercury drop electrode (SMDE) polarography using a modified version of the Cottrell equation with a spherical correction term was used to determine . At higher concentrations was determined chronopotentiometrically using the Sand equation. The values of in 0.51 M aqueous at 25°C were as follows , where is the stoichiometric concentration of (mol liter −1 ). At the higher concentrations estimates were made of the effects of migration on the measured values of . Transport number calculations, although nonrigorous, indicate that these effects are relatively minor.