Question

Determine the amount of urea (NH2CONH2) to be added in 1000 g of water to decrease its vapour presssure by 25%.
Given: Molar mass of N. C. O and H are 14. 12. 16 and 1 2 mol-1 respectively.

Answer 1

The correct answer is : 1111
$\frac{P^0-P_s}{P_s}=\frac{n_{solute}}{n_{solvent}}$
$=\frac{\frac{x}{60}}{\frac{1000}{18}}=\frac{P^0-0.75P^0}{0.75P^0}$
$⇒x=\frac{10000}{9}=1111\ \text{gm}$