The boiling point of a solvent containing a non-volatile solute:

Options

A. Depressed
B. Elevated
C. Does not change
D. None of these

Answer

To determine the effect of adding a non-volatile solute to a solvent on its boiling point, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Boiling Point**:
- The boiling point of a liquid is defined as the temperature at which its vapor pressure equals the atmospheric pressure. For water, this is typically 100°C (373.15 K) at 1 atmosphere.

2. **Effect of Non-Volatile Solute**:
- When a non-volatile solute (e.g., sucrose) is added to the solvent (e.g., water), it does not evaporate. This means that the number of solvent molecules that can escape into the vapor phase is reduced.

3. **Vapor Pressure Reduction**:
- The addition of the non-volatile solute decreases the vapor pressure of the solution because there are fewer solvent molecules available to exert vapor pressure.

4. **Requirement for Boiling**:
- Since the vapor pressure is now lower than it was for the pure solvent, the solution will need to be heated to a higher temperature to reach the point where the vapor pressure equals the atmospheric pressure.

5. **Elevation of Boiling Point**:
- The increase in temperature required for the vapor pressure of the solution to equal atmospheric pressure results in an elevated boiling point. This change in boiling point is known as boiling point elevation.

6. **Mathematical Relation**:
- The elevation in boiling point (ΔTb) can be expressed mathematically as:
\[ \Delta T_b = k_b \cdot m \]
where \( k_b \) is the ebullioscopic constant of the solvent and \( m \) is the molality of the solute.

7. **Conclusion**:
- Therefore, the boiling point of a solvent containing a non-volatile solute is elevated compared to that of the pure solvent.

### Final Answer:
The boiling point of a solvent containing a non-volatile solute is **elevated**.

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