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 equivalents of $CaC{O}_3$ is:
(molar mass of calcium bicarbonate is $162gmo{l}^{-1}$ and magnesium bicarbonate is $146gmo{l}^{-1}$)

• A. 10000 ppm
• B. 1000 ppm
• C. 5000 ppm
• D. 100 ppm

Answer 1

The correct option is A 10000 ppm

We know,
$n_{eq}CaC{O}_3=n_{eq}Ca(HC{O}_3{)}_2+n_{eq}Mg(HC{O}_3{)}_2$
Let, w is the mass of $CaC{O}_3$
$\frac{w}{100}\times 2=\frac{0.81}{162}\times 2+\frac{0.73}{146}\times 2$
$\Rightarrow w=1$
Mass of water = 100 g
Hardness of water $=\frac{1}{100}\times {10}^6=10000ppm$