Universal indicator
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 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]
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. The universal indicator is made from magnesium hydroxide with a pH value of 4.
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 | bgcolor="red" |Red |- |3-6 |Acid | bgcolor="yellow" |Orange/Yellow |- |7 |Neutral | bgcolor="limegreen" |Green |- |8-11 |Alkali | style="background:blue; color:white;" |Blue |- |> 11 |
Strong alkali | Violet/Purple |
See also
- Litmus test
- pH Indicator
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.L. and Gruntfest, J.Chem.Educ., 14, 274 (1937)
- ↑ "Universal Indicator". ISCID Encyclopedia of Science and Philosophy.