Solutions and Colligative Properties - Result Question 2
3. Liquid $M$ and liquid $N$ form an ideal solution. The vapour pressures of pure liquids $M$ and $N$ are $450$ and $700 $ $ mm Hg$, respectively, at the same temperature. Then correct statement is
(2019 Main, 9 April I)
$x _M=$ mole dfraction of $M$ in solution;
$x _N=$ mole dfraction of $N$ in solution;
$y _M=$ mole dfraction of $M$ in vapour phase;
$y _N=$ mole dfraction of $N$ in vapour phase
(a) $\dfrac{x _M}{x _N}>\dfrac{y _M}{y _N}$
(b) $\dfrac{x _M}{x _N}=\dfrac{y _M}{y _N}$
(c) $\dfrac{x _M}{x _N}<\dfrac{y _M}{y _N}$
(d) $\left(x _M-y _M\right)<\left(x _N-y _N\right)$
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Answer:
Correct Answer: 3. (a)
Solution:
Key Idea: For a solution of volatile liquids the partial vapour pressure of each component of the solution is directly proportional to its mole dfraction present in solution. This is known as Raoult’s law.
Liquid $M$ and $N$ form an ideal solution. Vapour pressures of pure liquids $M$ and $N$ are $450$ and $700$ $ mm Hg$ respectively.
$\therefore \quad p^{o}{ } _N>p^{o}{ } _M$
So, by using Raoult’s law
$\quad y_N > x_N \hspace{5mm}…(i)$
and $\quad x _M>y _M\hspace{5mm}…(ii)$
Multiplying (i) and (ii) we get
$y _N x _M>y _M x _N $
$\therefore \dfrac{x _M}{x _N}>\dfrac{y _M}{y _N}$
Thus, correct relation is (a).
BETA
