Bright Tutorials Bright Tutorials
ICSE Class 8 Chemistry Question 12 of 13

Water — Question 2

Back to all questions
2
Question

Question 21

Give balanced equations to show how -

(a) Temporary hardness enters into water.

(b) Temporary hardness in water can be removed by boiling.

(c) Permanent hardness in water can be removed by addition of washing soda.

Answer

(a) CaCO3 + H2O + CO2 ⟶ Ca(HCO3)2
MgCO3 + H2O + CO2 ⟶ Mg(HCO3)2

(b) Ca(HCO3)2 →boil\xrightarrow{\text{boil}} CaCO3 ↓ + H2O + CO2 [g]
Mg(HCO3)2 →boil\xrightarrow{\text{boil}} MgCO3 ↓ + H2O + CO2 [g]

(c) Na2CO3 washing soda+CaSO4 calcium sulphate⟶CaCO3↓+Na2SO4\underset{\text{ washing soda} }{\text{Na}_2\text{CO}_3} + \underset{\text{ calcium sulphate}}{\text{CaSO}_4} \longrightarrow \text{CaCO}_3 ↓ + \text{Na}_2\text{SO}_4