Freezing point depression of salt water
What is the freezing point of a 1.0 m aqueous NaCl solution? (Kf for water = 1.86 °C/m; assume full dissociation)
Answer B: explanation for every choice
A
This uses i = 3, as for CaCl₂.
B
Correct. ΔTf = iKfm = (2)(1.86)(1.0) = 3.72 °C, so the solution freezes at −3.72 °C.
C
This uses i = 1, ignoring dissociation into Na⁺ and Cl⁻.
D
This halves Kf.
TakeawayΔTf = iKfm. Count particles, not formula units.
Equation usedColligative properties
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