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
$P=120 \, X_{A}+138$ , here $X_{A}$ is mole fraction of methyl alcohol. What are the values of $\underset{X_{A \rightarrow 0}}{P_{limit}}$ and $\underset{X_{B \rightarrow 0}}{P_{limit}}$ ?

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

Answer 1

Answer: (A)

If $X_{A}=0$ , then pure $B$ is present.
$\therefore \, P^\circ _{B}=138$
If $X_{A}=1$ , then pure $A$ is present.
$\therefore \, P^\circ _{A}=120 \, + \, 138=258$