ELECTRON-TRANSFER REACTION-RATES AND EQUILIBRIA OF THE CARBONATE AND SULFATE RADICAL-ANIONS

Electron transfer reactions of the carbonate radical anion with azide, bromide, and hypochlorite ions have been studied by pulse radiolysis. From the equilibrium Br2.- + CO32- reversible 2Br- + CO3.- and the known redox potential for Br2.-/2Br- = 1.62 V vs NHE we derive E = 1.59 V for CO3.-/CO3.-. From this value and the equilibrium CO3.- + ClO- reversible CO32- + ClO. we derive E = 1.41 V for ClO./ClO-. The equilibrium reaction SO4.- + Cl- reversible SO42- + Cl. was studied by laser photolysis, by using 248 nm excitation of S2O82- to produce SO4.- and examining the rate of reaction of this radical with Cl- in the presence of varying concentrations of SO42-. By modeling the reactions taking place in this system, we derive the rate constant for the reaction of Cl. with SO42- (2.5 x 10(8) dm3 mol-1 s-1 at 0.1 mol dm-3 ionic strength), and from the known rate constant for reaction of SO4.- Cl- (4.7 x 10(8) dm3 mol-1 s-1 at the same ionic strength) we derive the equilibrium constant. From the known redox potential for Cl./Cl- = 2.41 V we derive E = 2.43 V for SO4.-/SO42-.