Litmus paper Blue

When a blue litmus paper changes to red after touching a substances, it means that the substances contains acid. Therefore, the substance is grouped as an acidic substance.

blue litmus paper changes to red

If a blue litmus paper does not change its colour after touching a substance, it can be means two thing:
i) The substance could be neutral
ii) The substance could be alkaline.

As such, we need to test the substance with a red litmus paper. If the red litmus paper does not change its colour, then the substance is neutral.


Addition knowledge:

Acids

Hydrochloric acid

• substances with a pH of less than 7 are acids
• the stronger the acid, the lower the pH number
• acids turn blue litmus paper red
• they turn universal indicator red if they are strong, and orange or yellow if they are weak.