Question: What is the freezing point depression of a solution containing 1 mol of NaCl in 1 kg of water? (Kf for water = 1.86 °C kg/mol) (2023)

Options:

1. 1.86 °C
2. 3.72 °C
3. 2.00 °C
4. 0.93 °C

Correct Answer: 3.72 °C

Exam Year: 2023

Solution:

Freezing point depression (ΔTf) = i * Kf * m. For NaCl, i = 2 (dissociates into Na+ and Cl-). m = 1 mol/kg. ΔTf = 2 * 1.86 °C kg/mol * 1 = 3.72 °C.