Freezing Point Depression Calculator
Calculate Freezing Point Depression
Find Molality from Depression
Molar Mass from Freezing Point
Determine molar mass of unknown solute from FP depression
Formula
ΔTf = i × Kf × m | New FP = Normal FP - ΔTf | Kf(water) = 1.86 °C·kg/mol
Frequently Asked Questions
What is freezing point depression?
Freezing point depression is the decrease in freezing point when a solute is added to a solvent. ΔTf = i·Kf·m, where Kf is the cryoscopic constant, m is molality, and i is the van't Hoff factor. It is a colligative property (depends on number of particles, not identity).
Why does salt lower the freezing point of water?
NaCl dissociates into Na⁺ and Cl⁻ (i=2), disrupting the crystal lattice formation. This lowers the freezing point by ΔTf = 2 × 1.86 × m. At saturation (~6.1 m), road salt can lower water's FP to about -21°C.
What is the cryoscopic constant?
Kf is a property of the solvent: Water = 1.86°C·kg/mol, Benzene = 5.12, Camphor = 40.0 (useful for molar mass determination due to large Kf). Higher Kf means greater sensitivity.
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