Question

The hardness of a water sample (in terms of equivalents of $CaC{O}_3$ ) containing ${10}^{–3}MCaS{O}_4$ is :
(molar mass of $CaS{O}_4=136gmo{l}^{–1}$)

• A. 10 ppm
• B. 90 ppm
• C. 50 ppm
• D. 100 ppm

Answer 1

The correct option is D 100 ppm

$\text{Moles of}CaS{O}_4={10}^{–3}mol\text{Mass of}CaS{O}_4={10}^{-3}\times 136$
$\text{Mass of}CaS{O}_4=0.136g$

$CaS{O}_4\to CaC{O}_3$
$136gofCaS{O}_4\to 100gofCaC{O}_3$
$0.136gofCaS{O}_4\to \frac{100}{136}\times 0.136$
$=0.1gofCaC{O}_3$
$\text{Hardness (in terms of}CaC{O}_3)=\frac{W_{CaC{O}_3}}{W_{H_{2}O}}\times {10}^{6}ppm$
$\text{Hardness (in terms of}CaC{O}_3)=\frac{{10}^{-1}}{1000}\times {10}^6=100ppm$

Hence, option (d) is correct.