Question

Freezing point of urea solution is \( -0.6^{\circ}\text{C} \). How much urea (\( \text{m.wt.} = 60 \text{ g/mol} \)) will be required to dissolve in 3 kg water? (\( k_{f} = 1.5^{\circ}\text{C kg mol}^{-1} \))

• A. 24 g
• B. 36 g
• C. 60 g
• D. 72 g

Hint:

Ensure mass of solvent (W) is in grams when using the 1000 factor in the formula.

Answer 1

The Correct Option is D

Step 1: Concept
$\Delta T_{f} = k_{f} \times m$, where $m$ is molality.
Step 2: Analysis
* $\Delta T_{f} = 0 - (-0.6) = 0.6^{\circ}\text{C}$. * $w = \frac{\Delta T_{f} \times M \times W}{k_{f} \times 1000}$. * $w = \frac{0.6 \times 60 \times 3000}{1.5 \times 1000}$.
Step 3: Conclusion
$w = 72 \text{ g}$.
Final Answer: (D)