Litmus paper Red

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

Red litmus paper changes to blue

If a red litmus paper does not change its colour after touching a substance, it can mean two things:
i) The substances could be neutral.
ii) The substances could be acidic.

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

Addition knowledge:

Alkalis

Sodium hydroxide

• Bases that dissolve in water are called alkalis.
• Copper oxide is not an alkali because it does not dissolve in water, but sodium hydroxideis an alkali because it does dissolve in water.
• Alkaline solutions have a pH of more than 7.
• The stronger the alkali, the higher the pH number.
• Alkalis turn red litmus paper blue.
• They turn universal indicator dark blue or purple if they are strong, and blue-green if they are weak.