30g of urea is dissolved in 846 g of water.calculate the vapour pressure of water for this solution if vapour pressure of pure water at 298 K is 23.8 mm Hg.

Dear Student,

The Raoult's law is used for computation and is expressed as below,

$\frac{{p_1}^o-p_1}{{p_1}^o}=\frac{n_2}{n_1+n_2}$

Number of moles = Mass / Molar mass 
Number of moles for water = 846 / 18 = 47
Number of moles for urea = 30 / 60 = 0.5

$$\begin{gathered} \frac{23.8-p_1}{23.8}=\frac{0.5}{47+0.5} \\ \Rightarrow p_1=23.549 mm Hg \end{gathered}$$

Regards.