Question

At $35^{o}C$ the vapour pressure of $CS_{2}$ is 512 mm Hg, and of acetone, $CH_{3}COCH_{3}$ , is 344 mm Hg. A solution of $CS_{2}$ and acetone in which the mole fraction of $CS_{2}$ is 0.25 has a total vapour pressure of 600 mm Hg. Which of the following statements about solution of acetone - $CS_{2}$ is true ?

• A. A mixture of 100 ml of acetone and 100 ml of $CS_{2}$ has a total volume of 200 ml.
• B. When acetone and $CS_{2}$ are mixed at $35^{o}C$ , heat must be absorbed in order to produce a solution at $35^{o}C$ .
• C. When acetone and $CS_{2}$ are mixed at $35^{o}C$ , heat is released.
• D. Raoult's law is obeyed by both $CS_{2}$ and acetone for the solution in which the mole fraction of $CS_{2}$ is 0.25.

Answer 1

Answer: (B)

$P_{T}=P_{A}^\circ X_{A}+P_{B}^\circ X_{B}=512\times 0.25+\left(344 \times 0 .75\right)=386$

∴ The solution is showing positive deviation

So For a solution of

$Acetone+CS_{2}; \, ΔH=+ve$