Question

One litre of a sample of hard water contains 55.5 mg of $CaC{l}_2$ and 4.75 mg of $MgC{l}_2$. The total harness in terms of ppm of $CaC{O}_3$ is :

• A. 9 ppm
• B. 10 ppm
• C. 20 ppm
• D. none of these

Answer 1

The correct option is D none of these

$55.5$ mg of $CaC{l}_2$ in 1 litre of water corresponds to $55.5$ ppm.

$4.75$ mg of $MgC{l}_2$ in 1 litre of water corresponds to $4.75$ ppm.

Also $1CaC{l}_2=1CaC{O}_3$

$111$ ppm $=100$ ppm

Hence, $55.5$ ppm $=\frac{100}{111}\times 55.5=50$ ppm.

Also $1MgC{l}_2=1CaC{O}_3$

$95$ ppm $=100$ ppm

Hence, $4.75$ ppm $=\frac{95}{111}\times 4.75=5$ ppm.

Hence, the total hardness will be $5$ ppm.