The rate of adsorption and adsorption displacement in the system hydroquinone-sulfite-iodide—II. Chronoamperometric measurements at a rotating gold disc electrode

Abstract

The rates of adsorption of iodide and of adsorption displacement of sulfite by iodide were measured at a rotating gold disc electrode in solutions containing hydroquinone. The reaction was initiated by a potential step from a cathodic state of total desorption to an anodic state of adsorption and parallel hydroquinone oxidation. The anodic current of hydroquinone was measured as a function of time. In solutions of pH = 8.1 the adsorption of iodide was diffusion controlled. The current decreased linearly with time and iodide concentration; it suddenly reached its final value as soon as about 1 3 of the electrode surface was covered. In sulfite containing solution at pH = 10.5 with small additions of iodide, first the current decreased rapidly corresponding to the diffusion of sulfite which covered the electrode surface. In the measure as iodide appeared at the surface, the current increased up to a limiting value which could be used to measure the adsorption equilibrium of iodide in presence of sulfite. The rate of sulfite displacement is determined by the diffusion rate of iodide. However, the rate of increase of current as well as the maximum current of hydroquinone is proportional to c 2 I−. It is assumed that hydroquinone is discharged the presence of adsorbed iodide via a bridge mechanism, the bridge consisting of about two iodide molecules.