Speculation on some effects of complexation and anion-induced adsorption on the polarography of indium in acidic halide and thiocyanate media

Some phenomena found in the polarographic reduction of indium (III) in acidic halide and thiocyanate media have been studied by a‐c polarography. Speculation on the role of complex formation and anion‐induced adsorption on the polarographic reduction at potentials near the half‐wave potential are given. At low ligand concentrations the a‐c peak potential is believed to be influenced by anion‐induced adsorption while at high ligand concentrations the value is the thermodynamic value predicted from bulk complexation equilibria. The unusual d‐c minimum found at more negative potentials and the above phenomena are discussed in terms of the coupled occurrence of electroinactive ions at potentials where the complexed ion is electroactive and anion‐induced adsorption. The reduction mechanism at the half‐wave potential and at more negative potentials are concluded to be similar. The irreversible reduction of the uncomplexed indium ion is attributed to the slow rate of exchange of co‐ordinated water, in agreement with other workers.