Chemistry - Liquid Solution Question with Solution | TestHub

Given, vapour pressure of benzene, $$p^{\circ }=640\mathrm{mm}\mathrm{Hg}$$ Vapour pressure of solution, $$p=600\mathrm{mm}\mathrm{Hg}$$ Weight of solute, $w=2.175\mathrm{g}$ Weight of benzene, $W=39.08\mathrm{g}$ Molecular weight of benzene, $$M=78\mathrm{g}$$ Molecular weight of solute, $m=?$ According to Raoult's law, $\begin{array}{rl}\frac{p^{\circ }-p}{p^{\circ }}& =\frac{w\times M}{m\times W}\\ \frac{640-600}{640}& =\frac{2.175\times 78}{m\times 39.08}\\ \frac{40}{640}& =\frac{2.175\times 78}{m\times 39.08}\\ m& =\frac{16\times 2.175\times 78}{39.08}\\ m& =69.60\end{array}$