SIMULTANEOUS ADSORPTION OF THIOUREA AND THIOCYANATE IONS ON MERCURY-ELECTRODES .1. INFLUENCE OF THIOUREA ON ANION ADSORPTION

The simultaneous adsorption of thiourea and thiocyanate ions on mercury has been investigated by differential capacity measurements in a total of 72 aqueous solutions. The influence of thiourea on thiocyanate adsorption is discussed in terms of the dependence of the potential of zero charge on concentration, the shape of the differential capacity curves, the dependence of the specifically adsorbed charge on the surface excess of thiourea and an isotherm based on the electrostatic model of the double layer, taking into account the ratio of the surfaces occupied by the organic molecule and the anion. The main observation is that at low thiocyanate concentrations the presence of thiourea induces an increase in the specifically adsorbed charge; however, as the concentration of the anion increases, the presence of thiourea inhibits the adsorption of thiocyanate.