Question

At ${400}^{o}C$, the vapour pressure of water is $55.3mmHg$. Calculate the vapour pressure at the same temperature over $10\%$ aqueous solution of urea $\left[CO\right(N{H}_2{)}_2]$?

Answer 1

$\frac{p^0-p}{p^0}=X_{urea}$

let the mass of solution be 100g

mass of urea =10g

M.wt of urea = 60; M.wt of water = 18

$X_{urea}=\frac{10}{60}=\frac{1}{6}$

$X_{water}=\frac{90}{18}=5;X_{urea}=\frac{1/6}{1/6+5}=\frac{1}{31}$

mole fraction of urea:

$=\frac{55.3-p}{55.3}=\frac{1}{31}$

$p=55.3\ast \frac{30}{31}=53.52mmHg$