Electrochemistry of high concentration copper chloride complexes.

High concentrations of copper chloride solutions (in the molar range) are used in several industrial applications. In this work, we investigated the species distribution of copper chloride complexes and how to measure the copper concentration precisely at high concentrations using electrochemical methods, by including migrational effects. The latter, in fact, can be useful in determining the nature of the species in solution undergoing electron transfer at the electrode. The study indicates that the main species of Cu(II) complexes in high chloride concentration is CuCl4(2-) and the main species of Cu(I) complexes are CuCl2(-) and CuCl3(2-). However insoluble CuCl is an intermediate in the process and can deactivate the electrode surface. This can be ameliorated by increasing the temperature or Cl(-) concentration. Under these conditions, voltammetry with an ultramicroelectrode (UME) can measure copper concentration with good precision even at 1 M Cu(II) concentrations in a few molar chloride. The main charge of the species can be determined by fitting to a migration model.