Kinetics of the reaction between a brompropionate and silver ions. A heterogeneous reaction taking place on the surface of silver bromide

Abstract

A detailed study of the kinetics of the reaction between a brompropionate and silver ions has been made in very dilute solutions at 27°C. The hydrolysis of the brompropionate ion in pure aqueous solutions is an extremely slow reaction. In very dilute solutions (below about 0·001 N) the reaction is an extremely slow one even when silver nitrate solution is added. The velocity of reaction becomes rapid only when some silver bromide is formed in suspension and an analysis of the data obtained in the investigation proves beyond all doubt that the reaction is almost entirely heterogeneous, taking place on the surface of silver bromide particles. In dilute solutions in which silver bromide exists in fine and stable suspension, it has been found that the velocity of reaction is strictly proportional to the amount of silver bromide in suspension. It is inferred from the order of the reaction that both silver and brompropionate ions are sparsely adsorbed on the surface of the silver bromide particles. In different experiments, when the initial concentration of one of the reactants is kept constant and that of the other increased, the amount of silver bromide in the different reaction mixtures at the beginning and end of the reaction being nearly the same, it has been found that the velocity constant gradually falls. This variation seems to indicate that as the ratio of the concentrations of the reactants increases under otherwise identical experimental conditions the relative orientation of the two kinds of ions in the adsorbed layer becomes less and less favorable for reaction.