Solutions and Colligative Properties - Result Question 43
####14. 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)
(2017 Adv.)
(a) The point $Z$ represents vapour pressure of pure liquid $M$ and Raoult’s law is obeyed from $x _L=0$ to $x _L=1$
(b) 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 $M$ and Raoult’s law is obeyed when $x _L \rightarrow 0$
(d) The point $Z$ represents vapour pressure of pure liquid $L$ and Raoult’s law is obeyed when $x _L \rightarrow 1$
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Solution:
- The graph shown indicates that there is positive deviation because the observed vapour pressure of $L$ is greater than the ideal pressure
Since, deviation is positive, the intermolecular force between $L$ and $M$ is smaller than the same in pure $L$ and pure $M$.
Also as $x _L \rightarrow 1, x _M \rightarrow 0$, the real curve approaching ideal curve where Raoult’s law will be obeyed.
