Indicators and the pH Scale

Looking further at the pH scale, which gives a range of numbers (corresponding to colours) when an indicator is put into an acid, alkali or a neutral substance.

The pH scale only works when you use universal indicator. The colours seen when applied will generate scores:

  • 0 – 6 pH, which indicates an acidic substance – from red to green
  • 7 pH, which indicates a neutral substance – green colour
  • 8 – 14 pH, which indicates an alkaline substance – from green to purple

However, there are other indicators you can use, such as litmus paper.

Litmus Paper

There are two different types of litmus paper, both red and blue.

Blue litmus paper turns red when put in an acidic solution

Red litmus paper turns blue when put in an alkaline solution