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ICSE Class 9 Chemistry Question 17 of 31

Water — Question 13

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13
Question

Question 1(xiii)

Temporary hardness of water can be removed by:

  1. Adding sodium chloride
  2. Boiling
  3. Adding calcium carbonate
  4. Leaving it for a few hours.
Answer

Boiling

Reason — By boiling carbon dioxide is driven off and the soluble hydrogen carbonates are converted into insoluble carbonates and could be removed by filtration or decantation.

Calcium carbonate and magnesium carbonate are precipitated leaving the water soft.

Ca(HCO3)2 →Boil \xrightarrow{\text{Boil}\space} CaCO3 ↓ + H2O + CO2 ↑

Mg(HCO3)2 →Boil \xrightarrow{\text{Boil}\space} MgCO3 ↓ + H2O + CO2 ↑