Question

What is the vapor pressure of a solution in which the mole fraction of the solute is 0.200 and the vapor pressure of the pure solvent is 100.0 torr? (Assume a single nonvolatile, nonelectrolyte solute).
a. 0 torr
b. 80.0 torr
c. 100.0 torr
d. 120.0 torr
e. 20.0 torr

Answer 1

Answer: The vapor pressure of a solution in which the mole fraction of the solute is 0.200 is 80.0 torr

Explanation:

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,

$\frac{p^o-p_s}{p^o}=i\times x_2$

where,

$p^0$= vapor pressure of pure solvent = 100.0 torr

$p_s$ = vapor pressure of solution = ?

i = Van'T Hoff factor = 1 for nonvolatile, nonelectrolyte solute

$x_2$ = mole fraction of solute  = 0.200  

$\frac{100.0-p_s}{100.0}=1\times 0.200$

$p_s=80.0torr$

The vapor pressure of a solution in which the mole fraction of the solute is 0.200 is 80.0 torr