Classification of the pH-Oscillatory Hydrogen Peroxide–Thiosulfate–Sulfite Reaction

Abstract

The reaction of hydrogen peroxide with thiosulfate and sulfite in acidic solution is characterized by marked temporal pH variations suggesting autocatalytic nature of hydrogen ions. When carried out in a continuous-flow stirred tank reactor this reaction provides nonlinear dynamical regimes including periodic oscillations, chaotic behavior, and multiple steady states coexisting over a range of operating conditions. The aim of the presented experimental study is a classification of the role of species and the underlying mechanism in the periodic oscillatory mode by applying single pulse additions of chosen reaction species. The external perturbations at various phases of the periodically oscillating system may cause phase advance or phase delay of the oscillations. The resulting phase transition curves are obtained for hydrogen ions, hydroxide ions, thiosulfate ions, sulfite ions, and hydrogen sulfite ions. These curves are compared with the phase transition curves calculated using the prototype mechanisms representing categories of chemical oscillators established in previous work. We found our system to be compatible with the mechanism of the category 1CX.

Use of Phase Transition Curves for Testing Models of the pH-Oscillatory Hydrogen Peroxide-Thiosulfate-Sulfite Reaction

“…When compared with the cross-point of type 1 PTC for hydrogen ion (Figure a) the location of cross-point is shifted to the left. This feature is consistent with our previous experimental results and leads to conclusion that with increasing amplitude of perturbation the cross-point is systematically shifting to the left. When a relatively large amplitude of perturbation is applied, a well-developed type 0 PTC with maximum and minimum is found (Figure b).…”

“…An experimental procedure used in this study follows the same principle and conditions as described in our previous work . After filling the reaction cell with both feed solutions the other external constraints were set to bring the reaction system to a regular oscillatory regime.…”

“…The stock solutions were kept carbon dioxide free also during the experiments by bubbling with nitrogen. The PTCs were measured as described in our previous work . Namely, a pulse addition to sustained pH-oscillations at phase φ is applied by injecting a chosen species.…”

“…Here 1 stands for first-order autocatalysis (most experimental systems fall in this group), B stands for batch system with internally generated negative feedback and C for continuous system with flow-assisted negative feedback. , At the Hopf bifurcation or in the oscillatory regime, various methods can be applied to determine the role and category, for example, by calculating mutual phase shifts of the essential species. In our previous work we examined the possibility of using the PTCs for that purpose and below we use those results to characterize alternative mechanisms for the HPTS reaction.…”

Design of non-autonomous pH oscillators and the existence of chemical beat phenomenon in a neutralization reaction

“…In the open system, realized in continuous stirred-tank reactors (CSTRs), in which the inflow of the reagents and outflow from the reactor are allowed and usually their flow rates are constant in time, offer the possibility to maintain the non-linear chemical systems far from their thermodynamic equilibria. pH oscillators (in which the concentration of the H + ions oscillates in time) fall into this type of oscillators and the existing range of the pH are in between acidic and neutral (e.g., bromate–sulfite oscillator 11 , 14 – 16 , hydrogen peroxide–sulfite oscillator 17 – 19 ) or neutral and alkaline (sulfite – formaldehyde–lactone oscillators 20 – 22 ) conditions. Due to their chemical mechanism, no oscillator has been designed and engineered which can oscillate between acidic and alkaline conditions and the greatest pH amplitude that can be achieved is around three pH units (ΔpH ~ 3) 23 .…”