Question

When 45 gm of a solute is added to 900 gm of water, its vapour pressure decreased from 30 mm to 24 mm. The mole fraction of the solvent in the solution is :

• A. $0.2$
• B. $0.8$
• C. $0.1$
• D. $0.9$

Answer 1

The correct option is B $0.8$

moles of water $=\frac{900}{18}$$=50$
According to Raoult's law, mole fraction of solvent $=\frac{P_{solvent}}{P_{solvent}^O}$
$=\frac{24}{30}$
$=\frac{4}{5}$
$=0.8$