1. Tardigrade
  2. Question
  3. Chemistry
  4. The vapour pressure of a solvent decreases by 10mm of Hg when a non-volatile solute was added to the solvent. The mole fraction of the solute in the solution is 0.2 . What should be the mole fraction of the solvent if the decrease in vapour pressure is found to be 20mm of Hg ?

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Q. The vapour pressure of a solvent decreases by $10mm$ of $Hg$ when a non-volatile solute was added to the solvent. The mole fraction of the solute in the solution is $0.2$ . What should be the mole fraction of the solvent if the decrease in vapour pressure is found to be $20mm$ of $Hg$ ?

NTA AbhyasNTA Abhyas 2020

Solution:

Case $-1$
$P^{0}-P_{s}=10\Rightarrow X_{B}=0.2$
$RWP=X_{B}$
$\Rightarrow \frac{10}{P ^\circ }=0.2\Rightarrow 50$
Case $-2$
$P^\circ -P_{s}^{'}=20\Rightarrow X_{A}=?$
Now, $\frac{20}{P ^\circ }=X_{B}$
$\Rightarrow \frac{20}{50}=X_{B}$
$\Rightarrow 0.4=X_{B}$
$\Rightarrow X_{A}=0.6$