Kinetics of Competitive Adsorption : Part III. Chloride and Bromide Ions on Silver and Aluminium

In continuation of our earlier work on competitive adsorption, the rates of adsorption of Cl^- and Br^-lens on silver and aluminium have been studied using ³⁶Cl and ⁸²Br. The adsorption of each ion from the mixed adsorbate of Cl^- and Br^- ions is suppressed (by above 60%) in presence of the competing ion. The rate of adsorption of Br^- ions, is however, fast both in presence or absence of Cl^- ions. The adsorption results are verified by a study of the desorption of the ions from their adsorbed films of 1, 5 and 20 layer-thickness in media of water and 10^-3 M. Nal, NaBr and NaCl solutions. The exchange desorption follows first order rate law: the rate constants being in the order k(Nal) > k(NaBr) > k(NaCl) > k(water). The results are consistent with the relative oxidation potentials for the electrodes Ag/AgCl(s)/Cl^- and Ag/AgBr(s)/Br^-.