Which of the following will show a negative deviation from Raoult’s law?

Options

A. Acetone-benzene
B. Acetone-ethanol
C. Benzene-methanol
D. Acetone-chloroform.

Answer

To determine which of the given pairs will show a negative deviation from Raoult's law, we need to analyze the intermolecular interactions between the components of each pair. Here’s a step-by-step solution:

### Step 1: Understand Raoult's Law
Raoult's law states that the vapor pressure of an ideal solution is directly proportional to the mole fraction of the solvent. Deviations from Raoult's law indicate non-ideal behavior, which can be either positive or negative.

### Step 2: Identify Types of Deviations
- **Positive Deviation**: Occurs when the intermolecular forces between different molecules (AB interactions) are weaker than the forces between similar molecules (AA and BB interactions).
- **Negative Deviation**: Occurs when the intermolecular forces between different molecules (AB interactions) are stronger than the forces between similar molecules (AA and BB interactions).

### Step 3: Analyze Each Pair
1. **Acetone and Benzene**:
- The intermolecular forces between acetone and benzene are weak. Therefore, AB interactions are weaker than AA and BB interactions, indicating positive deviation.

2. **Acetone and Ethanol**:
- Ethanol has strong hydrogen bonding. When mixed with acetone, the hydrogen bonding is disrupted, leading to weaker AB interactions compared to AA and BB interactions. This also indicates positive deviation.

3. **Benzene and Methanol**:
- Methanol has strong hydrogen bonding due to its OH group. Mixing it with benzene weakens the intermolecular forces, leading to weaker AB interactions compared to AA and BB interactions. This indicates positive deviation.

4. **Acetone and Chloroform**:
- Acetone and chloroform can form strong hydrogen bonds due to the presence of polar groups. The AB interactions are stronger than the AA and BB interactions, indicating negative deviation.

### Step 4: Conclusion
Based on the analysis, the pair that shows a negative deviation from Raoult's law is **Acetone and Chloroform**.

### Final Answer
**Acetone and Chloroform will show a negative deviation from Raoult’s law.**

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