Universal indicator

This article is about the chemical pH indicator. For the musical artists, see Universal Indicator (music).

A Universal indicator is a pH indicator composed of a blend of several compounds that exhibits several smooth colour changes over a pH value range from 1-14 to indicate the acidity or basicity 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, propan-1-ol, phenolphthalein sodium salt, sodium hydroxide, methyl red, bromothymol blue monosodium salt, and thymol blue monosodium salt.

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

pH range	Description	Colour
0-3	Strong acid	Red
3-6	Acid	Orange/Yellow
7	Neutral	Green
8-11	Base	Blue
11-14	Strong Base	Violet/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.

==See also==Universal Indicator, Adelaide vigilante.

Rumours abound in Adelaide of a vigilante, naming himself Universal Indicator, pointing out things that are wrong by videoing minor crime on his phone, and sending them to Police. Although never taking credit, and keeping his identity unknown, many believe he is a storeman in a chemical warehouse (hence the aka) named Wayne Johnstone. When confronted with these alleagations, Johnstone claimed "If I was going to be any sort of super hero, I'd model myself on Charlie Sheen and tell kids not to eat their vegetables, to stay in school cos work sucks and to give me their drugs". Universal Indicator is fast becoming an Urban myth, complete with copy cats.