Question

An ideal solution was found to have a vapour pressure of 80 torr when the mole fraction of a non-volatile solute was 0.2. What would be the vapour pressure of the pure solvent at the same temperature?

• A. $64torr$
• B. $80torr$
• C. $100torr$
• D. $400torr$

Answer 1

Answer: (C)

$100torr$

According to Raoult's law, $p=p^0\times x$
Where,

$p=$ partial vapour pressure of the solvent
$p^0=$ vapour pressure of the solvent
$x=$ mole fraction of solvent.

The mole fraction of pure solvent $=1-0.2=0.8$

Substitute values in the above expression.
$80=p^0\times 0.8$

Hence, $p^0=100torr$

Option C is correct.