Universal indicator

Universal indicator is a pH indicator that transitions through numbers 3-12 (on the pH chart) to indicate the acidity or alkalinity of solutions. Although there are a number of commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1923. 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.

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

The colours that indicate the pH of a solution, after adding universal indicator are:

0-3. Strong acid - Red

3-6. Acid - Orange/Yellow

7. Neutral - Green

8-11. Alkali - Blue

11-14. Strong Alkali - Purple

There are now also available wide range pH test papers with distinct colours for each pH from 1 to 14. Colour matching charts are supplied with the specific test strips purchased.