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  4. What is the mole fraction of toluene in the vapour phase at 300C above a benzene-toluene solution. The mole fraction of benzene in the solution phase is 0.400? (PB0 = 119 texttorr a n d PT0 = 37.0 text torr) , B stands for benzene and T stands for toluene

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Q. What is the mole fraction of toluene in the vapour phase at $30^{0}C$ above a benzene-toluene solution. The mole fraction of benzene in the solution phase is 0.400?
$\left(P_{B}^{0} = 119 \text{torr} a n d \, P_{T}^{0} = 37.0 \text{ torr}\right)$ , B stands for benzene and T stands for toluene

NTA AbhyasNTA Abhyas 2022

Solution:

$P=X_{A}P_{A}^{0}+X_{B}P_{B}^{0}$
Total pressure of the sol. is given by
$P_{T o t a l}=X_{B}P_{B}^{0}+X_{T}P_{T}^{0}$
$=0.4\times 119+0.6\times 37$
$=47.6+22.2=69.8 \, torr$
Applying Dalton's law for mole fraction in vapour phase
$Y_{B}=\frac{P_{B}}{P_{T o t a l}}=\frac{47.6}{69.8}=0.68194$
$Y_{T}=1-0.6819 \, =0.318$