Question

Hardness of a water sample is 100 ppm $CaCO_{3}$. Thus, molarity of $CaCO_{3}$ is

• A. $2 \times 10^{-3}\,M$
• B. $1 \times 10^{-3}\,M$
• C. $2 \times 10^{-2}\,M$
• D. $2 \times 10^{-4}\,M$

Answer 1

Answer: (B)

Hard water has hardness = 100 ppm
Thus, $10^{6}\,mL (=10^{3})$ water has $CaCO_{3}=100\,g=1\,mol$
Thus, molarity $=\frac{\text{Moles }}{\text{Litre}}$
$=\frac{1}{10^{3}}=1\times 10^{-3}\,M$