Question

At $48^{\circ }C$ the vapour pressure of pure $C{S}_2$ is $850torr$ . A solution of $2.0\text{g}$ of sulphur in $100g$ of $\text{C}{\text{S}}_2$ has a vapour pressure $844.9torr$ . Determine the atomicity of sulphur molecule.

• A. 1
• B. 2
• C. 4
• D. 8

Answer 1

Answer: (D)

$\Delta P=5.1torr$ ; x is atomicity of sulphur.
$\frac{\Delta P}{P_A^{{}^{\circ }}}=\frac{5.1}{850}=X_B=\frac{\frac{2}{32x}}{\frac{2}{32x}+\frac{100}{76}}$
$\frac{5.1}{850}\cong \frac{2}{32x}\times \frac{76}{100}$
$x=\frac{2\times 76}{32\times 100}\times \frac{850}{5.1}=7.92\approx 8$