Question

6g of urea is dissolved in 90g of boiling water.The vapour pressure of solution is

Answer 1

vapour pressure of a solution is 0.98 atm

Answer 2

Answer : The vapor pressure of solution is, 23.324 torr

Solution :

As the relative lowering of vapor pressure is directly proportional to the amount of dissolved solute.

The formula for relative lowering of vapor pressure will be,

$\frac{p^o-p_s}{p^o}=\frac{w_2M_1}{w_1M_2}$

where,

$p^o$ = vapor pressure of pure solvent  (water) = 23.8 torr

$p_s$ = vapor pressure of solution  = ?

$w_2$ = mass of solute  (urea) = 6 g

$w_1$ = mass of solvent  (water) = 90 g

$M_1$ = molar mass of solvent (water) = 18 g/mole

$M_2$ = molar mass of solute (urea) = 60 g/mole

Now put all the given values in this formula ,we get the vapor pressure of the solution.

$\frac{23.8-p_s}{23.8}=\frac{6\times 18}{90\times 60}$

$p_s=23.324torr$

Therefore, the vapor pressure of solution is, 23.324 torr