Question

Vapour pressure of solvent is 17.5 mmhg while that of a solution solution is 17.5 mmhg the mole fraction of the solvent is

Answer 1

Answer : The mole fraction of the solvent is, 1

Solution :

According to the relative lowering of vapor pressure, the vapor pressure of a component at a given temperature is equal to the mole fraction of that component of the solution multiplied by the vapor pressure of that component in the pure state.

Formula used :

$\frac{p^o-p_s}{p^o}=X_B$

where,

$p^o$ = vapor pressure of the pure solvent = 17.5 mmHg

$p_s$ = vapor pressure of the solution = 17.5 mmHg

$X_B$ = mole fraction of solute

Now put all the given values in this formula, we get the mole fraction of solute.

$\frac{17.5-17.5}{17.5}=X_B$

$X_B=0$

As, we know that

$X_A+X_B=1\\\\X_A=1-X_B\\\\X_A=1-0=1$

$X_A$ is the mole fraction of solvent.

Therefore, the moles of fraction of the solvent is, 1