Universal indicator

This article is about the chemical pH indicator. For the musical artists, see Universal Indicator (music).
A roll of universal indicator paper

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 1-14 to indicate the acidity or alkalinity of solutions. Although there are several commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1933.[1] Details of this patent can be found in Chemical Abstracts.[2] Experiments with Yamada's Universal Indicator are also described in the Journal of Chemical Education.[3]

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

pH range Description Colour
< 3 Strong Acid Red
3-6 Weak Acid Orange/Yellow
7 Neutral Green
8-11 Weak Base Blue
> 11 Strong Base Violet/Purple

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


See also

References

  1. ↑ Jap. Pat. 99,664, Feb 21, 1933
  2. ↑ Chem Abstr, 28, 2258 (1934)
  3. ↑ For a discussion of these experiments, as well as recipes for Yamada and other universal indicators, see Foster, S.L. and Gruntfest, J.Chem.Educ., 14, 274 (1937)
  4. ↑ "Universal Indicator". ISCID Encyclopedia of Science and Philosophy.