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=kH•[H+]•[HSO−3]•[H2O2], is valid at the low concentration level and at low ionic strength Ic. At 298 K and Ic=1.5×10−4 M, third-order rate constant kH was found to be kH=(9.1±0.5)×107 M−2 s−1. The temperature dependence of kH led to an activation energy of Ea=29.7±0.9 kJ mol−1. The effect of the ionic strength (adjusted with NaCl) on rate constant kH was studied in the range Ic=2×10−4–5.0 M at pH=4.5–5.2 by conductometry and stopped-flow spectrophotometry. The dependence of kH on Ic 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.