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. Details of this patent can be found in Chemical Abstracts.

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

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

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

See also

• Litmus paper

References