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

Diffusion coefficients for Cu(II), D Cu , were determined at 25°C in 0.51 M H 2 SO 4 over the concentration range 0.4 m M – 1.0 M CuSO 4 . The reported values of D Cu represent average values for the physical properties over the diffusion layer, and for the diffusing Cu(II) species, which consist of Cu ++ ions and Cu + + SO 4 = ion pairs. Thus, D Cu represents an effective value that is suitable for substitution into the various mass‐transfer equations derived by assuming constant properties. At low CuSO 4 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 D Cu . At higher CuSO 4 concentrations D Cu was determined chronopotentiometrically using the Sand equation. The values of D Cu in 0.51 M aqueous H 2 SO 4 at 25°C were as follows For CuSO 4 0 < 0.002 M : D Cu = 5.83 ± 0.08 1 × 10 − 6 cm 2 s − 1 , For 0.002 M < CuSO 4 0 < 1.0 M : 10 6 × D Cu = 6.33 + 2.69 log CuSO 4 0 + 1.62 log 2 CuSO 4 0 + 0.256 log 2 CuSO 4 0 where [ CuSO 4 ] 0 is the stoichiometric concentration of CuSO 4 (mol liter −1 ). At the higher CuSO 4 concentrations estimates were made of the effects of migration on the measured values of D Cu . Transport number calculations, although nonrigorous, indicate that these effects are relatively minor.