Question

Identify the mixture that shows positive deviations from Raoult's Law

• A. \( (\text{CH}_3)_2\text{CO} + \text{C}_6\text{H}_5\text{NH}_2 \)
• B. \( \text{CHCl}_3 + \text{C}_6\text{H}_6 \)
• C. \( \text{CHCl}_3 + (\text{CH}_3)_2\text{CO} \)
• D. \( (\text{CH}_3)_2\text{CO} + \text{CS}_2 \)

Answer 1

The Correct Option is D

To identify the mixture that shows positive deviations from Raoult's Law, we first need to understand the concept of Raoult's Law and deviations from it: 

• Raoult's Law: It states that the partial vapor pressure of a component in a mixture is directly proportional to its mole fraction in the solution and the vapor pressure of the pure component. It applies primarily to ideal solutions.
• Positive Deviation: A mixture shows positive deviation from Raoult's Law when the interactions between different molecules are weaker than interactions between like molecules. This causes the components to evaporate more easily, hence increasing the vapor pressure compared to what is predicted by Raoult's Law.

Now, let's analyze each given option for deviations:

1. \((\text{CH}_3)_2\text{CO} + \text{C}_6\text{H}_5\text{NH}_2\): In this mixture, acetone and aniline are involved. Aniline is capable of forming hydrogen bonds. Both interactions are different, and this can lead to deviation, but typically not positive as hydrogen bonding can strengthen interactions.
2. \(\text{CHCl}_3 + \text{C}_6\text{H}_6\): Chloroform (CHCl₃) and benzene (C₆H₆) form a mixture that shows deviations, but these are generally negative deviation due to the induction of dipoles.
3. \(\text{CHCl}_3 + (\text{CH}_3)_2\text{CO}\): Chloroform and acetone mixtures can show deviation; however, chloroform interacts strongly with acetone due to dipole-dipole interactions, often leading to negative deviation.
4. \((\text{CH}_3)_2\text{CO} + \text{CS}_2\): Acetone and carbon disulfide (CS₂) form mixtures where the interactions between unlike molecules (acetone and CS₂) are weaker than the interactions between like molecules. This causes a higher vapor pressure leading to a positive deviation from Raoult's Law.

Conclusion: Given the explanations for interactions and deviations, the correct answer is \((\text{CH}_3)_2\text{CO} + \text{CS}_2\). This mixture shows positive deviations from Raoult's Law due to weaker interactions between acetone and carbon disulfide than within the like pairs.

Answer 2

The mixture \((\text{CH}_3)_2\text{CO} + \text{CS}_2\) exhibits positive deviations from Raoult’s Law due to weaker intermolecular forces between the components compared to the pure substances.