A red–blue oscillating reaction

A glass Petri dish containing bromic acid, malonic acid and phenanthroline with a blue and red pattern

Source: © Getty Images

Use this practical or demonstration to provide a visual illustration of an oscillating reaction and redox equilibria. Includes kit list and safety instructions.

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.

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