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.[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]
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 [4]
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.
See also
References
- ↑ 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.
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