Question

Calculate the cryoscopic constant of solvent if depression in freezing point of 0.4 m solution of nonvolatile solute is 1.8 K .

• A. \( 4.0\text{ K kg mol}^{-1} \)
• B. \( 4.5\text{ K kg mol}^{-1} \)
• C. \( 5.1\text{ K kg mol}^{-1} \)
• D. \( 5.7\text{ K kg mol}^{-1} \)

Hint:

$K_f = \Delta T_f / m$. Cryoscopic constant is independent of the solute type, only dependent on the solvent.

Answer 1

The Correct Option is B

Step 1: Formula
$\Delta T_f = K_f \times m$.
Step 2: Substitution
$1.8 = K_f \times 0.4$.
Step 3: Calculation
$K_f = \frac{1.8}{0.4} = \frac{18}{4} = 4.5$.
Step 4: Conclusion
The cryoscopic constant is 4.5 K kg mol$^{-1}$.
Final Answer:(B)