The rate of reduction by solid silver of the chloro- and bromo-penta-amminecobalt(III) ions in aqueous acid solution

Abstract

Two silver rotating discs were used to study the redox reaction [Co(NH₃)₅Cl]²⁺+ Ag°+ 5H⁺→ AgCl + Co^II+ 5NH₄⁺ in aqueous perchloric acid solution at 25°. It was found that the rate of reaction at a clean silver surface was equal to the rate of transport of [Co(NH₃)₅Cl]²⁺ to the surface. During the course of the reaction the silver became coated with an adherent layer of silver chloride, which eventually decreased the rate. The heat of activation of the reaction was low, as expected for a transport-controlled process. The complex [Co(NH₃)₅Br]²⁺ reacted with silver in the same way.