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. ["Jap. Pat." 99,664, Feb 21, 1933] Details of this patent can be found in "Chemical Abstracts". ["Chem Abstr", 28, 2258 (1934)]

Experiments with Yamada's Universal Indicator are also described in the Journal of Chemical Education. [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)]

Details

*pH value: Approximately 7
*Vapour pressure: 25 mmHg (3.3 kPa)
*Vapour density: 1.3 kg/m³
*Molecular formula: Mixture
*Original colour: colourless

A universal indicator is typically composed of water, methanol, propan-1-ol, phenolphthalein sodium salt, methyl red sodium salt, bromothymol blue monosodium salt, and thymol blue monosodium salt [" [http://www.iscid.org/encyclopedia/Universal_Indicator Universal Indicator] ". ISCID Encyclopedia of Science and Philosophy.]

Here are the colours that indicate the acidity of a solution, after adding UI:

1. Very acidic - Red

2. Acidic - Orange/Yellow

3. Neutral - Green

4. Basic/base/alkali - Blue

5. Very basic/base/alkali - Purple

ee also

*Litmus paper

References