Q. If a solution containing 0.072 g atm of sulphur in 100 g of a solvent ($k_{f} = 7.0$) gave a freezing point depression of $0.84℃,$ the molecular formula of sulphur in the solution is
A) $S_{6}$
B) $S_{7}$
C) $S_{8}$
D) $S_{9}$
Explanation
(a)
Given, mass of solvent (w) =100 g
Depression in freezing point ($\mathrm{\Delta}T_{f}) = 0.84℃\ \ \ \ \ \$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ k_{f} = 7.0$ $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \frac{mass\ of\ solute(w)}{molecular\ mass\ of\ solue\ (M)} = 0.072$
$\mathrm{\Delta}T_{f} = \frac{1000 \times k_{f}}{n \times w}\left( \frac{w}{M} \right)$
0.84 =$\frac{1000 \times 7.0 \times 0.072}{n \times 100}$
n=6
$\therefore$ S is in $S_{6}$ form in solution.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.