Question

Which one of the following graphs accurately represents the plot of partial pressure of CS₂ vs its mole fraction in a mixture of acetone and CS₂ at constant temperature?

• A. 1
• B. 2
• C. 3
• D. 4

Hint:

Positive deviation is often associated with $\Delta H_{mix}>0$ (endothermic) and $\Delta V_{mix}>0$ (expansion upon mixing).

Answer 1

The Correct Option is A

To solve this question, we need to understand the concept of Raoult's Law and its application to mixtures like acetone and carbon disulfide (CS₂).

Raoult's Law states that the partial vapor pressure of each component in an ideal solution is directly proportional to its mole fraction. Mathematically, it is expressed as:

\(P_i = x_i \cdot P_i^0\)

where \(P_i\) is the partial vapor pressure of component i, \(x_i\) is the mole fraction, and \(P_i^0\) is the vapor pressure of the pure component.

In an ideal solution, the plot of partial pressure versus mole fraction is a straight line. The linear dependence means that if CS₂ behaves ideally in acetone, the graph of its partial pressure versus its mole fraction should be a straight line from the origin to \(P_{CS₂}^0\).

Observing the options:

1. Option 1 shows a straight line, indicating ideal behavior as predicted by Raoult's Law.
2. Option 2 and 3 show curves, which would indicate non-ideal behavior.
3. Option 4 demonstrates a combination of Raoult’s Law and Henry’s Law, where deviations from ideality are considered.

Since the question asks for a graph that accurately represents the plot of partial pressure vs. mole fraction at constant temperature for an ideal solution, the correct answer is Option 1.

Thus, the correct graph representing the plot of partial pressure of CS₂ versus its mole fraction is Option 1, reflecting the ideal solution behavior as per Raoult's Law.