pH Rainbow Tube

Introduction

In this demo, the teacher creates a beautiful rainbow of colours in a demonstration tube using universal indicator and a dilute
acid and base.

Discussion

Universal indicator can be used to illustrate an entire range of pH conditions because it is made up of a mixture of different
indicators that change colour at different pH values. As an acid is diluted with water, its pH increases—but never above pH 7.
Likewise, as a base is diluted, its pH decreases—but, again, never below pH 7. Continue reading