At , the vapour pressure of is 512 mm Hg and that of acetone , is 344 mm Hg. A solution of and aceto — Solutions and Colligative Properties Chemistry Question
Question
At $35^\circ\text{C}$, the vapour pressure of $\text{CS}_2$ is 512 mm Hg and that of acetone $\text{CH}_3\text{COCH}_3$, is 344 mm Hg. A solution of $\text{CS}_2$ and acetone, in which the mole fraction of $\text{CS}_2$ is 0.25 has a total vapour pressure of 600 mmHg. Which the following statement about solution of acetone and $\text{CS}_2$ is true?
💡 Solution & Explanation
The calculated ideal vapour pressure is $0.25(512) + 0.75(344) = 128 + 258 = 386 \text{ mm Hg}$. Since the observed pressure (600 mm Hg) is much higher, the solution exhibits a strong positive deviation from Raoult's law. This means interactions are weakened upon mixing, requiring an input of energy (endothermic process, $\Delta H_{mix} > 0$). Thus, heat is absorbed. Therefore, correct answer is C.