Freezing point depression: ΔT_f = K_f × m. For 0.5 molal NaCl (assume full dissociation, K_f = 1.86), the depression is:
- 0.46 K
- 0.93 K
- 3.72 K
- 1.86 K
Show answer and solution
Correct answer: D. 1.86 K
NaCl dissociates into 2 ions (i = 2 van't Hoff factor).
ΔT_f = i × K_f × m = 2 × 1.86 × 0.5 = 1.86 K. So 0.5 m NaCl freezes at -1.86°C.