Question

$2.56g$ of sulphur in $100g$ of $C{S}_2$ has depression in freezing point of $0.010^{\circ }C$.
Atomicity of sulphur in $C{S}_2$ is (Given, $K_f=0.1^{\circ }$ molal ${}^{-1}$ )

• A. 2
• B. 4
• C. 6
• D. 8

Answer 1

Answer: (D)

Let atomicity of sulphur is $n$, then it exists as $S_n$.
$\therefore$ Molar mass, $m=32n$
Now from,
$\Delta T_f=\frac{1000w{K}_f}{mw}$
$0.010=\frac{1000\times 2.56\times 0.1}{m\times 100}$
or $m=\frac{1000\times 2.56\times 0.1}{0.010\times 100}=256$
or $32n=256$
or, $n=\frac{256}{32}=8$