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 determine the vapor pressure of an aqueous solution of methanol in water, we can follow these steps:

### Step 1: Understand the Components
We have a solution consisting of two components: methanol (CH₃OH) and water (H₂O). In this case, water is the solvent, and methanol is the solute.

**Hint:** Identify the components of the solution and their roles (solvent vs solute).

### Step 2: Recognize the Nature of the Solution
The solution of methanol in water is a non-ideal solution. This means that the interactions between the molecules of methanol and water are different from the interactions between the molecules of water or methanol alone.

**Hint:** Recall that non-ideal solutions do not follow Raoult's Law perfectly.

### Step 3: Analyze the Mixing Process
In a non-ideal solution, the enthalpy change (ΔH) and the volume change (ΔV) during mixing are not zero. For methanol and water, the mixing process has a positive deviation from Raoult's Law, indicating that the interactions between methanol and water are weaker than the interactions among water molecules or among methanol molecules.

**Hint:** Understand that positive deviation means weaker interactions lead to an increase in vapor pressure.

### Step 4: Determine the Effect on Vapor Pressure
Since the solution exhibits a positive deviation, the vapor pressure of the solution will be higher than that predicted by Raoult's Law. This is because the tendency of the molecules to escape into the vapor phase increases when they are less strongly attracted to each other.

**Hint:** Remember that an increase in the tendency to escape leads to an increase in vapor pressure.

### Step 5: Compare Vapor Pressures
Given that the vapor pressure of the solution is influenced primarily by the solvent (water in this case), and since methanol is present in a smaller amount, the vapor pressure of the solution will be greater than that of pure water.

**Hint:** Compare the vapor pressures of the solution, water, and methanol to conclude which is greater.

### Conclusion
Thus, the vapor pressure of the aqueous solution of methanol in water will be greater than the vapor pressure of pure water.

**Final Answer:** The vapor pressure of the solution is greater than the vapor pressure of water.