Tuesday, 6 December 2011

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:


Litmus paper test - sodium hydroxide
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.

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