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 sulfite, HSO − 3, 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 +]·[HSO − 3]·[H 2O 2], is valid at the low concentration level and at low ionic strength I c. At 298 K and I c=1.5×10 −4 M, third-order rate constant k H was found to be k H=(9.1±0.5)×10 7 M −2 s −1. The temperature dependence of k H led to an activation energy of E a=29.7±0.9 kJ mol −1. The effect of the ionic strength (adjusted with NaCl) on rate constant k H was studied in the range I c=2×10 −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 semi-empirical relationship, which is useful for the purpose of comparison and extrapolation. The kinetic data obtained are critically compared with those reported earlier.