On pH and Ca2+ Oscillations Monitored by pH Electrode and Ca‐ISE in Bromate–Sulfite–Ferrocyanide System Introduced Ca‐EDTA

Abstract

The pH and Ca2+ oscillations of KBrO3–Na2SO3–K4Fe(CN)6 (BSF) system in presence of EDTA or Ca‐EDTA were investigated. Both EDTA and Ca‐EDTA can depress the amplitude and period of pH oscillation, and the effects of Ca‐EDTA are more obvious. These effects are attributed to the buffer effect in pH change. The Ca2+ oscillation appears as Ca‐EDTA introduced into the BSF system, which is ascribed to the stability of Ca‐EDTA being pH‐dependent. The pH and pCa (pCa = −log[Ca2+]) oscillations are synchronous in case of higher concentration of Ca‐EDTA; however, the chaotic behavior emerged in pCa oscillation arises at lower pH as the concentration of Ca‐EDTA is lower. Such observations can be understood by taking into account the interference of H+ on the response of Ca‐ISE to Ca2+. Both amplitude and period for pH and pCa oscillations as KCl introduced into the system can be obviously shortened due to the effect of ion strength on the reaction rate of the core oscillator and on the conditional formation constant of Ca‐EDTA. The results are significant for determining whether an experimentally observed chaos in chemical systems is of deterministic origin or is due to experimental noise.