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ICSE Class 9 Chemistry Question 16 of 31

Water — Question 3

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Question

Question 1(iii)

Permanent hardness of water is removed by:

  1. Adding calcium sulphate
  2. Boiling with potassium chloride
  3. Boiling
  4. Adding sodium carbonate
Answer

Adding sodium carbonate

Reason — Permanent hardness of water can be removed by addition of washing soda [sodium carbonate]:

Permanent Hard Water:

Na2CO3Washing soda+CaSO4Calcium sulphate⟶CaCO3↓Calcium carbonate+Na2SO4\underset{\text{Washing soda}}{\text{Na}_2\text{CO}_3} + \underset{\text{Calcium sulphate}}{\text{CaSO}_4} \longrightarrow \underset{\text{Calcium carbonate}}{\text{CaCO}_3↓} + \text{Na}_2\text{SO}_4