Question

Which of the following statements about the composition of the vapour over an ideal $1 : 1$ molar mixture of benzene and toluene is correct ? Assume that the temperature is constant at $25^{\circ} C$. (Given, Vapour Pressure Data at $25^{\circ} C$, benzene = $12.8\, kPa$, toluene = $3.85\, kPa$)

• A. The vapour will contain a higher percentage of toluene
• B. The vapour will contain equal amounts of benzene and toluene
• C. Not enough information is given to make a prediction
• D. The vapour will contain a higher percentage of benzene

Answer 1

Answer: (D)

V.P of $C_6 H_6 > $ V.P of $C_6 H_5 CH_3 $
$\because \, Y_A = \frac{P^{\circ}_A X_A}{P} , Y_B = \frac{P^{\circ}_B X_B}{P}$
$X_{A}$ and $X_{B}$ are same so mole fraction in vapour phase is directly proportional to the vapour pressure.