Question

What is an universal indicator?

Answer 1

A universal indicator is a pH indicator composed of a solution of several compounds that exhibits several smooth colour changes over a pH value range from 0 to 14 (it may be negative or higher depending on the concentration) to indicate the acidity or alkalinity of solutions, where 7 indicates neutral. Although there are several commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1933. Details of this patent can be found in Chemical Abstracts.Experiments with Yamada's universal indicator are also described in the Journal of Chemical Education.

A universal indicator is typically composed of water, propan-1-ol, phenolphthalein sodium salt, sodium hydroxide, methyl red, bromothymol blue monosodium salt, and thymol blue monosodium salt.

pH range Description Colour

< 3 Strong acid Red

3–6. Weak acid Orange

7 Neutral Green

8–11 Weak base Blue

> 11 Strong base Violet