Question

The plot of total vapour pressure as a function of mole fraction of the components of an ideal solution formed by mixing liquids $X$ and $Y$ is

• A.
• B.
• C.
• D.

Answer 1

Answer: (B)

According to Raoult's law,
$p=p^0\chi$
According to Dalton's law of partial pressure,
$p_T=p_x+p_y$
$p_T=p^{0}x{\chi }_x+p^0{}_y{\chi }_y$
$=p^{0}x{\chi }_x+p^{0}y\left(1-{\chi }_x\right)$
$p_T=p^0{}_Y+\left(p^0{}_x-p^{0}y\right){\chi }_x$
Thus, total vapour pressure of solution varies linearly with mole fraction of component $X$.
Case I, at ${\chi }_X=0$
$p_T=p^{0}Y$
Case II, at $X_X=1$
$p_T=p^{0}Y+p^{0}X-p^{0}Y$
$p_T=p_X^0$