pH-oscillations in a closed chemical system of CaSO3–H2O2–HCO3−

Abstract

Long-lasting large amplitude periodic change of the pH is measured in an aqueous suspension of CaSO₃–H₂O₂–HCO₃⁻ at 2.0–10.0 °C in a closed reactor. The amplitude can be as large as 2 pH units between pH 5 and 7. The observed phenomenon is explained and simulated by taking into account a slow dissolution of CaSO₃, which serves as a continuous supply of HSO₃⁻ for a H⁺-producing autocatalytic composite reaction between H₂O₂ and HSO₃⁻. Protonation of HCO₃⁻ to form CO₂ in a reversible reaction provides for the necessary negative feedback in [H⁺].