Solutions of sodium carbonate, potassium chloride and ammonium sulphate are taken in separate beakers.

Dip litmus paper (red, blue) in each beaker

i. Observe the colour change of litmus paper and tabulate.

ii. Name the acids and alkalies that react with each other to form each of the salts given above?

iii. Can you explain the colour change of the litmus paper on the basis of the nature of the acid and alkali that react with each other to form the salt?

(Hint: potassium chloride is a salt formed by the reaction between strong acid and strong alkali)

Litmus paper acts as an indicator to distinguish between acid and base. Blue litmus paper turns red in acidic medium and red litmus paper turns blue in basic medium.

i)

ii) The following acids and alkalies react to give the corresponding salts.

Acids and alkalies react to give salt and water.

•When a strong acid and a strong base react they give a neutral salt. Example: KCl

•When a strong acid and a weak base react they give an acidic salt. Example: (NH₄)₂SO₄

•When a weak acid and a strong base react they give a basic salt. Example: Na₂CO₃

iii) Litmus paper shows different colours in acidic and basic medium.

•When a strong acid and a strong alkali react, they give a neutral salt. Thus the litmus paper does not change its colour. Blue litmus paper remains blue and red litmus paper remains red. Example: KCl

•When a strong acid and a weak alkali react, they give an acidic salt. Thus blue litmus paper turns red and red litmus paper remains red. Example: (NH₄)₂SO₄

•When a weak acid and a strong alkali react, they give a basic salt. Thus red litmus paper turns blue and blue litmus paper remains blue. Example: Na₂CO₃