A red–blue oscillating reaction

In this experiment, students mix acidified sodium (or potassium) bromate and bromide solutions, before adding propanedioic (malonic) acid, ferroin indicator and a surface-active agent. They then observe the mixture as it exhibits oscillating patterns from red to blue over a period of several minutes.

The experiment provides an illustration of how a series of interconnected redox equilibria and their rates can lead to a repeating cycle of reactions, made visible by the inclusion of a suitable redox indicator.