Question

One litre of a sample of hard water (d =$1$ g/mL) contains $136$ mg of $CaS{O}_4$ and $190$ mg of $MgC{l}_2$. What is the total hardness of water in terms of $CaC{O}_3$?

• A. $100$ ppm
• B. $200$ ppm
• C. $300$ ppm
• D. None of the above

Answer 1

Answer: (C)

$300$ ppm

$136$ mg of $CaS{O}_4=100$ mg of $CaC{O}_3$
$190$ mg of $MgC{l}_2=2\times 100$ mg of $CaC{O}_3$
$1$ litre of $1000g$ water contain $300$ g of $CaC{O}_3$
${10}^6$ g water contains $\frac{300\times {10}^{-3}}{1000}\times {10}^6=300$ ppm

Hence, the total hardness of water in terms of $CaC{O}_3$ is $300$ ppm.