Kinetics of sulphur(IV) oxidation by hydrogen peroxide in basic aqueous solution

The reaction rate has been determined at low H+ concentration by spectrophotometric measurements. The kinetics were studied as a function of [SO32−], [H+] and total hydrogen peroxide concentration ([H2O2]total = [H2O2] + [H02−]). The rate law is expressed as: Rate= {(2.41 × 10−4 + 2.61 × 1010[H+])/(1 + 1.10 × 1011[H+])}[SO32−][H2O2]total with the experimental conditions : − log [H+] > 8.5; 1 moll−1 NaCl04; 25°C. The experimental data may be interpreted on the assumption that the most significant reactions are two bimolecular processes occurring between S032− and H2O2 and between S032− and HO2− (rate constants, respectively, k1 and k2). The rate constant k1 was determined for several concentrations of different ionic media NaCl04, NaCl and Na2SO4. The variation of k1 is written as a function of the ionic strength in the form of an extended Debye-Hu¨ckel formula. The value of k1 = 0.247 mol−1ls−1 was extrapolated to zero ionic strength at 25°C.