It is more convenient to obtain the molecular weight of an unknown solute by measuring the freezing point depression than by measuring the boiling point elevation because

Options

A. Freezing point depression is a colligative property wheras boiling point elevation is not.
B. Freezing point depressions are larger than boiling point elevations for the same solution.
C. Freezing point depressions are smaller than boiling point elevations for the same solution.
D. Freezing point depression depends more on the amount of the solute than boiling point elevation.

Answer

To solve the question regarding why it is more convenient to obtain the molecular weight of an unknown solute by measuring freezing point depression rather than boiling point elevation, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Freezing Point Depression and Boiling Point Elevation**:
- Freezing point depression refers to the lowering of the freezing point of a solvent when a solute is added.
- Boiling point elevation refers to the increase in the boiling point of a solvent when a solute is added.

2. **Colligative Properties**:
- Both freezing point depression and boiling point elevation are colligative properties, which means they depend on the number of solute particles in a solution, not the identity of the solute.

3. **Magnitude of Changes**:
- The change in freezing point (ΔTf) is generally larger than the change in boiling point (ΔTb) for the same concentration of solute. This is due to the nature of the solvent and the specific constants associated with freezing point depression (Kf) and boiling point elevation (Kb).

4. **Calculation of Molecular Weight**:
- The molecular weight (M) of the solute can be calculated using the formula:
\[ M = \frac{w \cdot R \cdot T_f}{K_f \cdot \Delta T_f} \]
for freezing point depression and
\[ M = \frac{w \cdot R \cdot T_b}{K_b \cdot \Delta T_b} \]
for boiling point elevation, where \(w\) is the mass of the solute, \(R\) is the gas constant, \(T_f\) and \(T_b\) are the temperatures, and \(K_f\) and \(K_b\) are the respective constants.

5. **Conclusion**:
- Since the change in freezing point is larger than the change in boiling point for the same amount of solute, it is more convenient and accurate to measure freezing point depression to determine the molecular weight of an unknown solute.

### Final Answer:
It is more convenient to obtain the molecular weight of an unknown solute by measuring freezing point depression because the change in freezing point (depression) is larger than the change in boiling point (elevation) for the same solution.