The dissolution of copper metal by acidified iron(III) in acetonitrile-water solutions

Abstract

The kinetics and electrochemistry of the dissolution of a rotating copper disc in various acidified acetonitrile-water mixtures containing iron(III) as the oxidant are described. The reaction kinetics were investigated by a chronopotentiometric method in which the time taken for a copper film of known thickness to dissolve was determined. The reaction was shown to be diffusion-controlled over the temperature range (270-304 K) and composition range (1.0-14.5 mol dm^-3 acetonitrile) investigated, good agreement being obtained between rate constants calculated from kinetic measurements and those calculated from electrochemical (cathodic polarization) measurements. From these and kinematic viscosity data, diffusion coefficients for iron(III) in acetonitrile-water mixtures were calculated. It was found that, associated with a discontinuous change in the kinematic viscosity at 290 K, there was a corresponding change in the diffusion coefficient. The activation energy for the high-temperature diffusion process was lower than that for the low-temperature process. It was also found that the diffusion coefficient decreased with increasing acetonitrile concentration.

Corrosion potential measurements as a function of disc rotation speed and iron(III) concentration are reported. From these measurements, it was inferred that the anodic reaction is under mixed control.