Universal indicator

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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 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 Red
3-6 Acid Orange/Yellow
7 Neutral Green
8-11 Alkaline Blue
> 11 Strong alkaline Violet/Purple

See also[edit]

References[edit]

  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.