Question

At $40^{\circ }C$ , the vapour pressure (in $torr$ ) of methyl alcohol $\left(A\right)$ and ethyl alcohol $\left(B\right)$ solution is represented by
$P=120X_A+138$ , here $X_A$ is mole fraction of methyl alcohol. What are the values of $\underset{X_{A\to 0}}{P_{limit}}$ and $\underset{X_{B\to 0}}{P_{limit}}$ ?

• A. $138258$
• B. $258138$
• C. $120138$
• D. $138125$

Answer 1

Answer: (A)

If $X_A=0$ , then pure $B$ is present.
$\therefore P_B^{\circ }=138$
If $X_A=1$ , then pure $A$ is present.
$\therefore P_A^{\circ }=120+138=258$