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
Colours of 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 several commercially available universal pH indicators, most are a variation of a formula patented by Yamada[disambiguation needed] 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

The colours from yellow to red indicate an acidic solution,colours light blue to dark blue indicate bases and green colour that a solution is neutral.

Universal indicator components
Indicator Low pH color Transition pH range High pH color
Thymol blue (first transition) Red 1.2 – 2.8 Yellow
Methyl red Red 4.4 – 6.2 Yellow
Bromothymol blue Yellow 6.0 – 7.6 Blue
Thymol blue (second transition) Yellow 8.0 – 9.6 Blue
Phenolphthalein Colorless   8.3 – 10.0 Fuchsia

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.

Types of Universal Indicator[edit]

Color Change of Universal Indicator after immersing into Basic NaOH solution.
Universal Indicator Test Kit
Color Change of Universal Indicator after immersing into a Neutral solution

A universal indicator is collectively a mixture of indicators which show a color change in a solution,which interprets how acidic or basic a solution is.

A universal indicator can be in paper form or present in a form of a solution.[5]

  • Paper form: Is a strip of colored paper which changes color to red if the solution is acidic and to blue if the solution is basic. The strip can be placed directly onto a surface of a wet substance or few drops of the solution can be dropped onto the universal indicator using a dropping equipment. If the test solution is in dark color, it is preferable to use paper universal indicator.
  • Solution: The main components of a Universal indicator, in the form of a solution, are thymol blue, methyl red, bromothymol blue and phenolphthalein. This mixture is important because, each component, loses or gains electrons depending upon the acidity or basicity of the solution being tested. It is beneficial to use this type of a universal indicator in a colorless solution. This is will increase the accuracy of indication.

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, L. S.; Gruntfest, I. J. (1937). "Demonstration experiments using universal indicators". Journal of Chemical Education 14 (6): 274. doi:10.1021/ed014p274.  edit
  4. ^ "Universal Indicator". ISCID Encyclopedia of Science and Philosophy.
  5. ^ Walker, Denise (2007). Acids and alkalis (1 ed.). London: Evans. p. 13. ISBN 0-237-53002-3. Retrieved 4 June 2015.