Kinetics of the oxidation of hydrogen sulfite by hydrogen peroxide in aqueous solution: ionic strength effects and temperature dependence

Conductometry was used to study the kinetics of the oxidation of hydrogen s ulfite, HSO3-, by hydrogen peroxide in aqueous non-buffered solution at the low concentration level of 10(-5)-10(-6) M, typically found in cloud water . The kinetic data confirm that the rate law reported for the pH range 3-6 at higher concentration levels, rate = k(H).[H+].[HSO3-].[H2O2], is valid a t the low concentration level and at low ionic strength I-c. At 298 K and I -c= 1.5 x 10(-4) M, third-order rate constant k(H) was found to be k(H) = ( 9.1 +/- 0.5) x 10(7) M-2 s(-1). The temperature dependence of k(H) led to a n activation energy of E-a = 29.7 +/- 0.9 kJ mol(-1). The effect of the ion ic strength (adjusted with NaCl) on rate constant kH was studied in the ran ge I-c = 2 x 10(-4)-5.0 M at pH = 4.5-5.2 by conductometry and stopped-flow spectrophotometry. The dependence of k(H) on I-c can be described with a s emi-empirical relationship, which is useful for the purpose of comparison a nd extrapolation. The kinetic data obtained are critically compared with th ose reported earlier. (C) 1999 Elsevier Science Ltd. All rights reserved.