A New pH Oscillator: The Chlorite−Sulfite−Sulfuric Acid System in a CSTR

A new pH oscillator has been discovered involving the system of NaClO 2, Na 2 SO 3, and H 2 SO 4 in a continuous-flow stirred tank reactor (CSTR). While ClO 2 - serves as an oxidant in numerous systems exhibiting nonlinear dynamical behavior, this is the first reported chlorite-based pH oscillator. Large-amplitude oscillations in pH and potential of a platinum electrode were observed over a rather narrow concentration range. Complex dynamical behavior also was observed, including aperiodic oscillations, bistability between steady states, bistability between steady state and oscillatory state, bursting, a possible third steady state, and damped oscillations in batch. Autocatalytic oxidation of HSO 3 - by ClO 2 - is a major source of positive feedback in H + . A fast Cl + -transfer reaction between HOCl and SO 3 2- is an important source of negative feedback. Oscillations were also obtained in the presence of Na 2 CO 3, with the dehydration reaction of H 2 CO 3 providing additional negative feedback. Models are proposed to account for observed behavior using computer simulations. Comparisons are made to the ClO 2 - −I - and ClO 2 −I - oscillating systems, as well as to the general model for chlorite-based chemical oscillators proposed by Rabai and Orban. A possible mechanism for chemical coupling is proposed.