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.
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 a universal indicator are:
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.
^ Jap. Pat. 99,664, Feb 21, 1933
^ Chem Abstr, 28, 2258 (1934)
^ For a discussion of these experiments, as well as recipes for Yamada and other universal indicators, see Foster, S.F. and Gruntfest, J.Chem.Educ., 14, 274(1937)
^ “Universal Indicator”. ISCID Encyclopedia of Science and Philosophy.
Categories: PH indicators