An interface reaction of Hexavalent chromium: The polarographic behaviour of HCrO₄^- and CrO₄^2-

Abstract

Current-voltage relationships have been determined for the electroreduction of dilute chromate solutions in a range of bicarbonate-carbonate buffers at the dropping mercury electrode. Double waves are obtained whose relative heights are a function of the pH value. By analogy with the behaviour of pyruvic acid an interface reaction with some proton donor prior to the reduction to the trivalent state is suggested (CrO₄^2- +HB^- → HCrO₄^- + B^-). The rate constants for the interface reaction are computed for different donors by the method of Koutecky and Brdicka (1947). Adsorption-desorption processes in the region of the electrocapillary zero may account for the shape of the current-voltage curves, and, if so, the explanation based simply on an interface reaction will require modification. The occurrence of interface reactions and of adsorption-desorption processes in other inorganic systems is discussed.