Question

What is the degree of hardness of a sample of water containing $24mg$ of $MgS{O}_4$ (mol. mass $120$) per kg of water?

• A. $10ppm$
• B. $15ppm$
• C. $20ppm$
• D. $25ppm$

Answer 1

The correct option is C $20ppm$

Given, $1$ $kg$ of water contains $24$ $mg$ of $MgS{O}_4$.

So $1$ $kg=1000$ $g$ of water.

$1$ million $grams$ of water $=1000\times 1000$ $g$ contains $24$ $mg\times 1000=24$ $g$ of $MgS{O}_4$

$1$ $mole$ of $MgS{O}_4=1$ $mole$ of $CaC{O}_3$

$120$ $g$ of $MgS{O}_4=100$ $g$ of $CaC{O}_3$

$24$ $g$ of $MgS{O}_4=\left(x\right)$ $g$ of $CaC{O}_3$

So, $x=\frac{24\times 100}{120}=20$

So, degree of hardness $=20$ $ppm$

Hence, option C is correct.