where k (M^− 2 s^− 1) can be determined from thein the pH range 2 to 5, from 5 to 40 °C and 0.01 to 1 M.The effect of pH and ionic strength on the reaction suggest that the rates are due towhere H₂A = H₂CrO₄, HA = HCrO₄⁻, H₂B = H₂SO₃ and HB = HSO₃⁻. The overall rate expression over the investigated pH range can be determined fromwith k_H2A−H2B = 5.0 × 10⁷, k_HA–H2B = 1.5 × 10⁶ and k_H2A–HB = 6.7 × 10⁷.Fe(III) in the range 1.5 to 20 μM exerts a small catalytic effect on the reaction and significantly lowers the initial concentration of Cr(VI) compared to the nominal value. Contrary to Fe(III), formaldehyde (20 to 200 μM) reacts with S(IV) to form the hydroxymethanesulfonate adduct (CH₂OHSO₃⁻), which does not react with Cr(VI). Major cations Mg²⁺ and some minor elements such as Ba²⁺ and Cu²⁺ did not affect the rates. The application of this rate law to environmental conditions suggest that this reaction may have a role in acidic solutions (aerosols and fog droplets). This reaction becomes more important in the presence of high Fe(III) and low HMS concentrations, contributing to affect the atmospheric transport of chromium species and the distribution of redox species of chromium, which reach surface water from atmospheric depositions.  相似文献   

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