Question

For a solution formed by mixing liquids L and M, the vapour pressure of L plotted against the mole fraction of M in solution is shown in the following figure. Here $x_L$ and $x_M$ represent mole fractions of L and M, respectively, in the solution. The correct statement(s) applicable to this system is/are:

• A. Attractive intermolecular interactions between L-L in pure liquid L and M-M in pure liquid M are stronger than those between L-M when mixed in solution
• B. The point Z represents vapour pressure of pure liquid M and Raoult’s law is obeyed when $x_L\to 0$
• C. The point Z represents vapour pressure of pure liquid L and Raoult’s law is obeyed when $x_L\to 1$
• D. The point Z represents vapour pressure of pure liquid M and Raoult's law is obeyed from $x_L=0to{x}_L=1$

Answer 1

Answer: (A), (C)

The correct options are
A Attractive intermolecular interactions between L-L in pure liquid L and M-M in pure liquid M are stronger than those between L-M when mixed in solution
C The point Z represents vapour pressure of pure liquid L and Raoult’s law is obeyed when $x_L\to 1$

From the graph it is clear that there is positive deviation in the partial vapour pressure of L in solution to w.r.t pure L. Therefore option A is correct.

When $x_L\to 1$, then Z will have value equal to $P_L^0$ (vapour pressure of pure L).Therefore option C is also correct.

$P_L^0=x_L\times P_{Total}$ so when $x_M=0$ then $x_L=1$
$P_L^0=1\times P_{Total}$ = Z in given graph, so its obeys Raoult`s law