Infinite-Dilution Diffusion Coefficients of Complex Ions from Solution Conductivity Data

A technique is presented for determining infinite-dilution diffusion coefficients of complex ions from solution conductivity data. The method involves measuring the conductivities of dilute solutions in which the distribution of complex ions is systematically varied and statistically regressing the data to an equation that effectively relates individual ion diffusion coefficients to solution conductivity. The procedure is simple and requires no specialized equipment to perform. Unlike methods that require a concentration gradient, the solution composition is homogeneous and at equilibrium during measurements, which is a significant advantage when labile complexes are being studied. In this paper, diffusion coefficients of cuprous cyanide complexes are determined. Statistical analysis yields the infinite-dilution diffusion coefficients of Cu(CN)₂^-, Cu(CN)₃^2-, and Cu(CN)₄^3- at 25 °C as 1.43 × 10^-5 ± 9%, 1.08 × 10^-5 ± 9%, and 6.21 × 10^-6 ± 22% cm²/s, respectively.