Photo by C Lloyd at SSERC (Public Domain)

A classic demonstration (From the RSC) to show an indicator at work.

A long tube such as a burette is filled with acid, alkali and universal indicator.

Inverting the tube creates a pH gradient along the length of the tune which show up as different colours thanks to the universal indicator.

We also have a different (foolproof) version that can be carried out in any container that uses concentrated sodium carbonate solution to make a density/concentration gradient.

Rainbow Reaction

Rainbow reaction – SSERC Concentration gradient version

Rainbow Reaction – Risk Assessment