Question

What mass of CaO will be required to remove the hardness of 1000L of water containing 1.62g of calcium bicarbonate per liter?

Answer 1

Mass of calcium bicarbonate = 1000L × 1.62 g = 1620 g
Reaction is given by,
Ca(HCO₃)₂ + CaO ⇒ 2CaCO₃ + H₂O
Here it is clear that,
1 mol of Ca(HCO₃)₂ consumes 1 mole of CaO
∴ (40 + 2 + 120)g/mol = 162g/mol of Ca(HCO₃)₂ is consumed 56g/mol of CaO
∴ 1 g of Ca(HCO₃)₂ is consumed 56/162 g of CaO
∴1620 g of Ca(HCO₃)₂ is consumed 56/162 × 1620 = 560g of CaO

Hence, mass of CaO = 560g = 0.56 kg