An aqueous solution of methanol in water has vapour pressure

Options

A. Equal to that of water
B. Equal to that of methanol
C. More than that of water
D. Less than that of water

Explanation

To solve the question regarding the vapor pressure of an aqueous solution of methanol in water, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Raoult's Law**:
- Raoult's Law states that the vapor pressure of a solution is directly proportional to the mole fraction of the solvent in the solution. It can be mathematically expressed as:
\[ P_{solution} = X_{solvent} \cdot P^0_{solvent} \]
where \( P_{solution} \) is the vapor pressure of the solution, \( X_{solvent} \) is the mole fraction of the solvent, and \( P^0_{solvent} \) is the vapor pressure of the pure solvent.

2. **Identify the Components**:
- In this case, the solvent is water and the solute is methanol. We need to determine how the presence of methanol affects the vapor pressure of the solution.

3. **Consider Ideal vs Non-Ideal Solutions**:
- If the solution behaves ideally, the vapor pressure would be calculated using Raoult's Law. However, methanol and water form hydrogen bonds, which can lead to non-ideal behavior.
- Non-ideal solutions can exhibit positive or negative deviations from Raoult's Law.

4. **Analyze the Interactions**:
- In the case of methanol and water, the hydrogen bonding between methanol molecules (solute-solute) and water molecules (solvent-solvent) is stronger than the hydrogen bonding between methanol and water (solute-solvent).
- This indicates that the interactions between the solute and solvent are weaker than the interactions within the pure components.

5. **Determine the Type of Deviation**:
- Since the solute-solvent interactions (methanol-water) are weaker than the solute-solute (methanol-methanol) and solvent-solvent (water-water) interactions, this results in a positive deviation from Raoult's Law.
- Therefore, the vapor pressure of the solution will be higher than expected based on Raoult's Law.

6. **Conclusion**:
- The vapor pressure of the aqueous solution of methanol in water will be higher than that of pure water but less than that of pure methanol. Thus, the correct answer to the question is that the vapor pressure of the methanol-water mixture is more than that of water.

### Final Answer:
The vapor pressure of an aqueous solution of methanol in water is more than that of water.