Question

The hardness of a water sample containing ${10}^{-3}MMgS{O}_4$ expressed as $CaC{O}_3$ equivalents (in ppm)is (molar mass of $MgS{O}_4$ is 120.37 g/mol)

Answer 1

Hardness of water is measured in ppm in terms $CaC{O}_3$.
$n_{CaC{O}_3}=n_{MgS{O}_4}$
ppm is the parts (in grams ) present per million i.e. ${10}^6$
1000 mL has ${10}^{-3}$ moles of $MgS{O}_4$
Grams of $CaC{O}_3$ in $1mL=\frac{{10}^{-3}\times 100}{1000mL}$ grams
Hardness = $\frac{{10}^{-3}\times 100}{1000mL}\times {10}^6$ =100