Indicators and the pH Scale

The pH Scale is a numerical scale that measures how acidic or alkaline a solution is. The scale ranges from 0 (which is very acidic), to 14 (which is very alkaline).

  • Acidic substances have a pH number lower than 7 – From red to green
  • Alkaline solutions have a PH level greater than 7 – Is a green colour
  • Neutral solutions have a pH level equal to 7 – From green to purple


An indicator is a substance that changes colour due to a change in pH.

Universal indicator

Universal indicator is an acid-alkali indicator that can be used as a more precise measurement of pH. It produces colours that can be compared to the colour chart at the top, to provide an accurate value of pH.

Litmus Paper

Litmus paper is paper that has been treated with a mixture of dyes. The two types of litmus paper are blue and red.

  • Blue litmus paper turns red when put in an acidic solution
  • Red litmus paper turns blue when put in an alkaline solution