Question

100 ml of a water sample contains 0.81 g of calcium bicarbonate and 0.73 g of magnesium bicarbonate. The hardness of this water sample expressed in terms of equivalent of CaCO₃ is ______.

[Molar mass of calcium bicarbonate is 162 g mol^-1 and magnesium bicarbonate is 146 g mol^-1)

Options

• 5000 ppm

• 1000 ppm

• 100 ppm

• 10000 ppm

Answer 1

100 ml of a water sample contains 0.81 g of calcium bicarbonate and 0.73 g of magnesium bicarbonate. The hardness of this water sample expressed in terms of equivalent of CaCO₃ is 10000 ppm.

Explanation:

Molecular weight of calcium bicarbonate = 162

Molecular weight of magnesium bicarbonate = 146

Molecular weight of calcium carbonate = 100

162 g of \[\ce{Ca(HCO3)2}\] = 100 g CaCO₃

0.81 g of \[\ce{Ca(HCO3)2}\] = `100/162 xx 0.81` g CaCO₃

= 0.5 g CaCO₃

146 g of Mg(HCO₃)₂ = 100 g of CaCO₃

0.73 g of Mg(HCO₃)₂ = `(100 xx 0.73)/146` g of CaCO₃ 

= 0.5 g CaCO₃

100 ml of sample water contains (0.5 + 0.5) g = 1 g CaCO₃

Thus hardness of water sample = `(1 xx 10)/100` = 10,000 ppm