# The flocculation value of HCl for arsenic sulphide sol. is 30 m

Question:

The flocculation value of $\mathrm{HCl}$ for arsenic sulphide sol. is $30 \mathrm{~m}$ mol $\mathrm{L}^{-1}$. If $\mathrm{H}_{2} \mathrm{SO}_{4}$ is used for the flocculation of arsenic sulphide, the amount, in grams, of $\mathrm{H}_{2} \mathrm{SO}_{4}$ in 250 $\mathrm{mL}$ required for the above purpose is______________ .

(molecular mass of $\mathrm{H}_{2} \mathrm{SO}_{4}=98 \mathrm{~g} / \mathrm{mol}$ )

Solution:

(0.37)

For $1 \mathrm{~L}$ sol $30 \mathrm{~m} \mathrm{~mol}$ of $\mathrm{HCl}$ is required

$\therefore$ For $1 \mathrm{~L}$ sol $15 \mathrm{~m} \mathrm{~mol} \mathrm{H}_{2} \mathrm{SO}_{4}$ is required

For $250 \mathrm{~mL}$ of sol, $\mathrm{H}_{2} \mathrm{SO}_{4}$ required

$=\frac{15}{1000} \times 250 \mathrm{~m} \mathrm{~mol} \mathrm{H}_{2} \mathrm{SO}_{4}$

$=3.75 \mathrm{~m} \mathrm{~mol}$ of $\mathrm{H}_{2} \mathrm{SO}_{4}$

$1 \mathrm{~mol} \mathrm{H}_{2} \mathrm{SO}_{4}=98 \mathrm{~g}$

$3.75 \mathrm{~m}$ mol of $\mathrm{H}_{2} \mathrm{SO}_{4}$

$=3.75 \times 98 \times 10^{-3}$

$=0.3675 \mathrm{~g} \mathrm{H}_{2} \mathrm{SO}_{4}$