The simultaneous adsorption of iodide and thiocyanate ions on mercury: Part I. Specifically adsorbed charges

Abstract

The simultaneous adsoprtion of iodide and thiocyanate on mercury electrodes from a aqueous mixed solutions of NaI+NaSCN has been studied through measurements of the double-layer capacity at 298 K. Eighty-one solutions of composition xμ M NaI+(1 - x)μ M NaSCN were studied; x, the molar fraction of NaI, was varied between 0 and 0.75, and μ, the ionic strength, was varied between 0.01 and 1.0 M. The parameters of the double layer were obtained using the method proposed by Lakshmanan and Rangarajan, through a suitable computer program. It is shown that the two anions can be specifically adsorbed at the same time and that inhibition of the adsorption of one anion by that of the other can occur simultaneously for some of the mixed solutions. A comparative analysis of the specifically adsorbed charge of each anion is carried out for different solutions, mixed or not. The influence of the variation of the activity coefficients of the salts on the values of the specifically adsorbed charges is also discussed.