Kinetics of the silver(I)-catalyzed decomposition of peroxodisulphate in aqueous solution

Abstract

The kinetics of the silver(I)-catalyzed decomposition of the peroxodisulphate ion have been investigated in aqueous solution. Molecular oxygen is produced due to the decomposition of the peroxodisulphate ion in the presence of silver(I) ion. The rate of this decomposition and of the formation of oxygen is first order with respect to the concentrations of peroxodisulphate and silver(I) ions, and the rate of reaction obeys the expression –d[S₂O₈^2–]/dt= 2 d[O₂]/dt=k[Ag⁺][S₂O₈^2–], where k= 9.37 × 10^–3, 8.96 × 10^–3, 7.59 × 10^–3, 6.91 × 10^–3, and 6.92 × 10^–3 dm³ mol^–1 s^–1 at /= 0.03, 0.04, 0.06; 0.09, and 0.10 mol dm^–3 at 25°C, respectively; k= 1.83 × 10⁷ exp [–54 200 J mol^–1/RT] dm³ mol^–1 s^–1 at five temperatures between 21 and 40 °C and at l= 0.10 mol dm^–3. The silver(I)-ion concentration remains constant throughout the reaction, which is composed of a silver(I)-catalyzed chain reaction. The rate of the silver(I)-catalyzed decomposition of peroxodisulphate is not influenced by the addittion of cerium(III) ion, but greatly accelerated by acrylamide and/or copper(II) ion, and retarded by acrylonitrile. The formation of oxygen due to the reaction is completely retarded by the addition of cerium(III) ion. On the other hand, absorption of oxygen occurs in the case of the addition of acrylamide and acrylonitrile. Mechanisms are proposed to account for the results obtained.