Freezing Point Depression Calculator
Calculate freezing point depression using ΔTf = i × Kf × m. Supports water, benzene, camphor, and cyclohexane. Includes van't Hoff factor for ionic solutes like NaCl and CaCl₂.
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ΔTf (Freezing Point Depression)
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New Freezing Point —
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mol/kg
°C·kg/mol
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ΔTf
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New Freezing Point —
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°C·kg/mol
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ΔTf
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New Freezing Point —
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How to Use This Calculator
- Enter the molality of your solution (mol solute per kg solvent).
- Select or enter the cryoscopic constant Kf for your solvent.
- Enter the van't Hoff factor i (1 for non-electrolytes, ~1.85 for NaCl).
- Enter the pure solvent freezing point (0 °C for water).
- Results show ΔTf and the new freezing point.
Formula
ΔTf = i × Kf × m
New Freezing Point = FP₀ − ΔTf
Where: i = van't Hoff factor, Kf = cryoscopic constant (°C·kg/mol), m = molality (mol/kg)
Example
Example: 1 mol NaCl (i = 1.85) dissolved in 1 kg water (Kf = 1.86): ΔTf = 1.85 × 1.86 × 1 = 3.44 °C. New freezing point = 0 − 3.44 = −3.44 °C.
Frequently Asked Questions
- Freezing point depression is a colligative property: adding a solute to a solvent lowers its freezing point. The depression ΔTf = i × Kf × m, where i is the van't Hoff factor, Kf is the cryoscopic constant, and m is molality.
- NaCl dissociates into Na⁺ and Cl⁻ ions (i ≈ 1.85), effectively increasing the particle concentration in solution. More particles means a greater disruption of the ice lattice, requiring a lower temperature to freeze.
- Water's Kf is 1.86 °C·kg/mol. A 1 molal aqueous solution of a non-dissociating solute freezes at −1.86 °C instead of 0 °C.
- The van't Hoff factor (i) accounts for the number of particles a solute produces in solution. Glucose (i = 1), NaCl (i ≈ 1.85), CaCl₂ (i ≈ 2.7). Higher i means greater colligative effect.
- Ethylene glycol does not dissociate (i = 1) but is added in large quantities (high molality). A 50% ethylene glycol/water solution reaches roughly −37 °C freezing point, protecting car engines in winter.
Related Calculators
Sources & References (5) ▾
- Colligative Properties — ACS Chemistry for Life — American Chemical Society
- OpenStax Chemistry 2e, Chapter 11: Solutions and Colloids — OpenStax
- IUPAC Compendium of Chemical Terminology — Cryoscopic Constant — IUPAC
- NIST Chemistry WebBook — Thermophysical Properties of Water — NIST
- Atkins' Physical Chemistry, 11th Ed. — Chapter 5: Simple Mixtures — Oxford University Press