The vapour pressure of a solution of the liquids $\mathrm{A}$ $\left(\mathrm{p}^{\circ}=80 \mathrm{~mm}…

The vapour pressure of a solution of the liquids $\mathrm{A}$ $\left(\mathrm{p}^{\circ}=80 \mathrm{~mm} \mathrm{Hg}ight.$ and $\left.\mathrm{x}_{\mathrm{A}}=0.4ight)$ and $\mathrm{B}\left(\mathrm{p}^{\circ}=120 \mathrm{~mm} \mathrm{Hg}ight.$ and
$\mathrm{x}_{\mathrm{B}}=0.6$ ) is found to be $100 \mathrm{~mm} \mathrm{Hg}$. It shows that the solution exhibits
  1. positive deviation from ideal behaviour
  2. negative deviation from ideal behaviour
  3. ideal behaviour
  4. positive deviation for lower conc. and negative for higher conc.

Solution

$\quad P_{\text {total }}=p_{A}^{o} \times x_{A}+p_{B}^{o} \times x_{B}$
$=80.0 \times 0.4+120.0 \times 0.6=104 \mathrm{~mm} \mathrm{Hg}$
The observed $\mathrm{P}_{\text {total }}$ is $100 \mathrm{~mm} \mathrm{Hg}$ which is less than
$104 \mathrm{~mm}$ Hg. Hence the solution shows negative deviation.

Asked in: JEE-TOPICTESTS-CHEMISTRY

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