QJEEM05Ch0499: JEE Main 2005 Chemistry - Class 12 JEEM05Ch0499 Solution: Benzene and toluene form nearly ideal solutions. At 20 o C, the …

Given, Vapour pressure of benzene $$=75torr$$

Vapour pressure of toluene $$=22torr$$

mass of benzene in $$=78g$$

hence moles of benzene $$=\frac{78}{78}=1mole$$

(mol. wt of benzene $$=78$$)

mass of toluene in solution $$=46g$$

hence moles of toluene $$=\frac{46}{92}=0.5mole$$

Total moles of benzene and toluene = 1.5 mol

now partial pressure of benzene

$$={P^{\circ }}_b\times X_b=75\times \frac{1}{1+0.5}$$

$$=75\times \frac{1}{1.5}=75\times \frac{2}{3}=50$$ torr