Question

The vapour pressure of pure benzene at a certain temperature is $650mm$ Hg. A non-volatile and non-electrolyte solid weighing $1.54g$ is added to $26.00g$ of benzene. The vapour pressure of the solution is $600mm$ Hg. The molecular weight of solid substance is_______g $mo{l}^{-1}$
Give your answer as the nearest integer.

Answer 1

Answer: 60

$\frac{p_A^o-p_T}{p_A^o}=\frac{650-600}{650}=\frac{1}{13}$
$\therefore \frac{p_A^o-p_T}{p_A^o}=\frac{W_B}{M_B}\times \frac{M_A}{W_A};\frac{1}{13}=\frac{1.54\times 78}{M_B\times 26.00}$ ;
$\therefore M_B=\frac{1.54\times 78\times 13}{26.00}=60.06gmo{l}^{-1}$