Question

At 35${}^{\circ }$C, the vapour pressure of $C{S}_2$ is 512 mm Hg and that of acetone is 344 mm Hg. A solution of $C{S}_2$, 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 $C{S}_2$, and 100 mL acetone has a volume < 200 mL
• C. $C{S}_2$, 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)

$<br/>P_{\text{total }}=P_T=P_A^0{X}_A+P_B^0{X}_B<br/>$
The maximum value $X_A$ can hold is 1 , and hence the maximum value of $P_T$ should be $512mm$ 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.
$<br/>\Delta V_{\text{mix }}>0,\Delta H_{\text{mix }}>0<br/>$$\Rightarrow \left(1\right){\Delta }_{sol}H>0,\left(2\right)$ Raoult's law is not obeyed
$\left(3\right){\Delta }_{sol}.Volume>0$
$\left(4\right)C{s}_2$ and Acetone are less attracted to each ether than to themselves.