sblock Elements - Result Question 58
####9. The hardness of a water sample (in terms of equivalents of $CaCO _3$ ) containing is
(Molar mass of $CaSO _4=136 g mol^{-1}$ ) (2019 Main, 12 Jan I)
(a) $100 ppm$
(b) $10 ppm$
(c) $50 ppm$
(d) $90 ppm$
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Answer:
Correct Answer: 9. (d)
Solution:
- Hardness of water sample can be calculated in terms of ppm concentration of $CaCO _3$.
Given, molarity $=10^{-3} M$
i.e. $1000 mL$ of solution contains $10^{-3}$ mole of $CaCO _3$.
$\therefore$ Hardness of water $=$ ppm of $CaCO _3$
$$ \begin{aligned} & =\frac{10^{-3} \times 1000}{1000} \times 10^{6} \ & =100 ppm \end{aligned} $$
