Question

The hardness of a water sample containing $10^{- 3}M \, MgSO_{4}$ expressed as $CaCO_{3}$ equivalents (in ppm) is

(molar mass of $MgSO_{4}$ is 120.38 $g / m o l$ and molar mass of $CaCO_{3}$ is 100.08 $g / m o l$ )

• A. 50
• B. 75
• C. 90
• D. 100

Answer 1

Answer: (D)

Given: $10^{- 3}M \, MgSO_{4}$

i.e. $10^{- 3}$ mole $MgSO_{4}$ present in 1 litre solution

$n_{M g S O_{4}}=n_{C a C O_{3}}$

Mass of $CaCO_{3}=10^{- 3}\times 100$

ppm (in terms of $CaCO_{3}$ ) $=\frac{m a s s \, o f \, C a C O_{3 \, }}{w e i g h t \, o f \, so l u t i o n}\times 10^{6}$

ppm (in terms of $CaCO_{3}$ ) $=\frac{1 0^{- 3} \times 100}{1000}\times 10^{6}=100 \, ppm$