Question

The hardness of water sample containing 0.002 mole of magnesium sulphate dissolved in a litre of water is expressed as:

• A. $200ppm$
• B. $120ppm$
• C. $20ppm$
• D. $2000ppm$

Answer 1

The correct option is A $200ppm$

The hardness of water is calculated in terms of $CaC{O}_3$

$MgS{O}_4=0.002mole$

Amount of $MgS{O}_4=0.002\times 120\times 1000$ (Gram molecular wait per mole in milli grams )

$=240mg$

Now we need to convert $MgS{O}_4$ in respect to $CaC{O}_3$

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

$120g/mole$ $=$ $100g/mole$

$120mg$ $=$ $100mg$

$240mg$ $=$ $200mgofCaC{O}_3$

$\Rightarrow 240mgMgS{O}_4$ $=$ $200mgCaC{O}_3$

$\Rightarrow 1mg/L$ $=$ $1ppm$

$\Rightarrow \therefore$ Hardness of $H_{2}O$ $=$ $200ppm$

$Hencethecorrectanswerisoption\left(A\right)$