Question

At 35$^{\circ}$C, the vapour pressure of $CS_2$ is 512 mm Hg and that of acetone is 344 mm Hg. A solution of $CS_2$, in acetone has a total vapour pressure of 600 mm Hg. The false statement amongst the following is :

• A. heat must be absorbed in order to produce the solution at 35$^{\circ}$C
• B. a mixture of 100 mL $CS_2$, and 100 mL acetone has a volume < 200 mL
• C. $CS_2$, and acetone are less attracted to each other than to themselves
• D. Raoult's law is not obeyed by this system

Answer 1

Answer: (B)

$
P _{\text {total }}= P _{ T }= P _{ A }^{0} X _{ A }+ P _{ B }^{0} X _{ B }
$
The maximum value $X_{A}$ can hold is 1 , and hence the maximum value of $P_{T}$ should be $512 mm$ of $Hg$ which is less than the value of $P _{ T }$ observed. (600mm of $Hg$ )
Therefore +ve deviation from Raoult's law is observed.
This implies that $A - A$ interactions and $B - B$ interactions are stronger than $A - B$ interactions.

As, we know for a system not obeying Raoult's law and showing +ve deviation.
$
\Delta V _{\text {mix }}>0, \Delta H _{\text {mix }}>0
$$\Rightarrow \, \left(1\right)\Delta_{sol} H>\, 0, \left(2\right) $ Raoult's law is not obeyed
$\left(3\right) \Delta_{sol} . Volume \, >\, 0 $
$\left(4\right)Cs_{2}$ and Acetone are less attracted to each ether than to themselves.