What is a Universal Indicator?

Universal Indicator is a chemical used to measure the acidity or alkalinity of a substance.

A universal indicator is basically a pH indicator. It is a mixture of several compounds that exhibits several smooth colour changes over a wide range of pH values.

pH is a measurement of the acidity or alkalinity of a substance. Alkaline substances have pH values greater than 7, acidic substances have pH values less that 7 and neutral substances have a pH value of 7.

A universal indicator can be in paper form or in solution form.

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Universal Indicator Paper

universal indicator paper

A roll of universal indicator paper. Image Source

Universal indicator paper is a strip of coloured paper which changes colour according to the solution being tested. To test pH, the strip can either be placed directly on a surface of a moist substance or few drops of the solution to be tested can be dropped onto the universal indicator using a dropper.

Universal indicator paper is preferably used when the solution to be tested is darker.

Universal Indicator Solution

Colours of universal indicator solution

Colours of universal indicator solution. Image Source

Universal indicator solution is a solution of:

  • Water
  • 1-Propanol
  • Phenolphthalein
  • Sodium hydroxide
  • Methyl red
  • Bromothymol blue
  • Sodium bisulphite
  • Thymol blue

Universal indicator solution is preferable if solution is colourless. This increases the accuracy of indication.

Colours of the Universal Indicator

The colours that indicate the pH of a solution, after adding a universal indicator, are:

  • yellow to red indicate an acidic solution
  • blue to violet indicate alkali
  • green colour indicate a neutral solution.
pH rangeDescriptionColour
< 3Strong acidRed
3–6Weak acidOrange or Yellow
8–11Weak alkaliBlue
> 11Strong alkaliIndigo or Violet

However, the colors are usually specific to the formulation of the universal indicator and therefore a commercial preparation supplied together with colour matching charts that explains the expected colors and pH ranges.

Sydney Chako

Mathematics, Chemistry and Physics teacher at Sytech Learning Academy. From Junior Secondary School to Tertiary Level Engineering Mathematics and Engineering Science.


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