Question

5 g sulphur is present in 100 g of $CS_{2}.\Delta T_{b}$ of solution 0.954 and $K_{b}$ is 4.88. The molecular formula of sulphur is

• A. $S_{2}$
• B. $S_{4}$
• C. $S_{3}$
• D. $S_{8}$

Answer 1

Answer: (D)

$ΔT_{b}=K_{b}\times m$

$m=\frac{\Delta T_{b}}{K_{b}}$

or $\frac{W_{2} \times 1000}{M_{2} \times W_{1}}=\frac{\Delta T_{b}}{K_{b}}$

or $\frac{5 \times 1000}{M_{2} \times 100}=\frac{0.954}{4.88}$

$M_{2}=256$

Atomic weight of sulphur = 32

Number of sulphur atom $=\frac{M o l e c u l a r \, \text{weight}}{A t o m i c \, \text{weight}}=\frac{256}{32}=8$

Hence Molecular formula $=S_{8}$ .