Solvation and salt effects in the reaction of hydrogen peroxide with iodide ion at high iodide concentrations

Abstract

The first-order decomposition of hydrogen peroxide in neutral aqueous solution has been studied by a simple thermal technique in solutions containing high concentrations of several iodides. The derived second-order constants for the primary formation of Ol^– are similar to those obtained at the same cation concentrations in the presence of other salts but under much slower reaction rate conditions (Iow I^– concentration). No new kinetic feature therefore appears at the faster rates and the marked salt effect with alkali and alkaline-earth metals is principally attributable to the cation. The explanation that acceleration is due to the incorporation of H₂O₂ into the cation solvation sheath is supported by the observation that molal-BaCl₂ has no detectable effect upon the relative activities of H₂O and H₂O₂, as indicated by vapour analyses. Substituted ammonium ions, NH₄⁺ itself, and Cd²⁺ all slow the reaction.