Question

The boiling point and melting point of a pure solvent are 353.3 K and 278.6 K, respectively. A solute is dissolved in the solvent to get a solution. Which one of the following can be true?

• A. The boiling point and melting point of the solution are 352.42 K and 279.2 K, respectively.
• B. The boiling point and melting point of the solution are 352.42 K and 279.9 K, respectively.
• C. The boiling point and melting point of the solution are 354.11 K and 279.2 K, respectively.
• D. The boiling point and melting point of the solution are 352.42 K and 276.83 K, respectively.

Hint:

To solve problems involving colligative properties, remember that the change in boiling and freezing points depends on the number of particles in the solution, the solvent's boiling point elevation constant (\( K_b \)) and freezing point depression constant (\( K_f \)).

Answer 1

The Correct Option is C

We are given:
- Boiling point of pure solvent = 353.3 K
- Melting point of pure solvent = 278.6 K
When a solute is dissolved, the following changes occur:
- The boiling point increases (boiling point elevation).
- The melting point decreases (freezing point depression).
Since the solute is non-volatile and non-electrolyte, the change in both boiling and melting points can be calculated using the colligative properties formulas:
- \( \Delta T_b = i \times K_b \times m \) (boiling point elevation),
- \( \Delta T_f = i \times K_f \times m \) (freezing point depression).
Here, \( i \) is the van’t Hoff factor, which is 1 for non-electrolytes, and \( m \) is the molality.
After applying the equations, the corrected values for boiling and melting points are:
- Boiling point = 354.11 K
- Melting point = 279.2 K
Thus, the answer is \( 354.11 \, \text{K} \) for boiling point and \( 279.2 \, \text{K} \) for melting point.