Problem and Solution of UV–Vis Time-Based Measurements of a Chemical System Involving Gas Product: Application to the Bray–Liebhafsky Oscillatory Reaction

Abstract

Ultraviolet (UV)−visible (Vis) spectroscopy is widely used in all modern laboratories as a routine method of analysis. The monitoring of chemical reactions in an aqueous solution involving a gas product is a demanding task but particularly for oscillatory reactions which are obtainable in a narrow concentration range. In this work, the optimization of experimental conditions for UV−Vis measurements of the Bray− Liebhafsky (BL) oscillatory reaction producing oxygen was done by using an internal standard. After applying the method of the internal standard on iodine absorbance at 460 nm, the characteristic BL oscillatory parameters (and iodine changes) are clearly evident. The obtained results allow students to apply their existing knowledge and, through a simple experimental setup, understand the importance of the internal standard, but at the same time, they show how they can solve the problem of UV−Vis noise during the time-based measurements of reactions involving gas products in general.

A mathematical model of the Bray–Liebhafsky reaction

“…It has been reported that the reaction turns yellow due to the presence of iodine and faintly changes hue. Some experiments report periodic evolution of oxygen from the solution [4]. However, drawing on our own, admittedly limited, experimental work [5], we have found that the solution turns yellow after an induction period but no subsequent visually distinguishable periodic colour change was seen.…”

Turing Patterns in the Chlorine Dioxide-Iodine-Malonic Acid Reaction–Diffusion Batch System

“…Classroom demonstrations of oscillatory chemical reactions have become a valuable pedagogical tool to introduce students to a variety of chemical concepts including kinetics, thermodynamics and catalysis . Over the past 50 years, nonlinear chemical dynamics has been the subject of numerous articles in this Journal . − Such works span experimental demonstrations of oscillations and waves through the BZ and BR reactions, ,,,,, the mercury beating heart, the gas evolution oscillator, the chemiluminescent oscillator, , pH oscillators, the salt-water oscillator, , the explosion oscillator, and the Liesegang rings, − to the theoretical presentation of the foundations of nonlinear dynamics, ,,,, and nonequilibrium thermodynamics . Most of these classroom demonstrations focused on oscillations in stirred systems and propagating waves in unstirred systems.…”