The freezing point depression calculator computes how much adding a solute lowers the freezing point of a solvent using ΔTf = i × Kf × m. Essential for antifreeze calculations, road salt analysis, and colligative property problems.
Freezing Point Depression (ΔTf = i·Kf·m)
NaCl=2, CaCl₂=3, glucose=1
How to Use the Freezing Point Depression Calculator
Freezing point depression explains why roads don't freeze at 0°C after salting and why antifreeze protects car engines in winter. The formula is ΔTf = i × Kf × m.
How Antifreeze Works
Ethylene glycol (i=1, MW=62.07 g/mol) dissolved in water. A 50/50 v/v mix ≈ 5.4 mol/kg molality. ΔTf = 1 × 1.853 × 5.4 ≈ 10°C. Wait — actually 50/50 ethylene glycol/water protects to about -37°C due to additional effects. The colligative formula is approximate for concentrated solutions.
Road Salt Example
Road salt is mainly NaCl (i=2) and CaCl₂ (i=3). For 1 m NaCl: ΔTf = 2 × 1.853 × 1 = 3.706°C. Freezing point = 0 − 3.706 = −3.706°C. CaCl₂ at 1 m: ΔTf = 3 × 1.853 × 1 = 5.559°C. CaCl₂ is more effective per mole and works to lower temperatures.
Cryoscopy for Molar Mass
Dissolve a known mass of unknown compound in a known mass of camphor (Kf = 40 °C·kg/mol). Measure ΔTf. Then m = ΔTf / (i × Kf), and molar mass = (g solute / kg camphor) / m. Camphor's large Kf makes the freezing point depression measurable even for small samples.
FAQ
What is freezing point depression?
Freezing point depression is a colligative property: adding solute to a solvent lowers its freezing point. ΔTf = i × Kf × m, where i is the van't Hoff factor (number of particles per formula unit), Kf is the cryoscopic constant, and m is molality. The new freezing point = normal freezing point − ΔTf.
How does antifreeze work?
Ethylene glycol (antifreeze) dissolved in water lowers the freezing point of the coolant. A 50/50 mixture of ethylene glycol and water (roughly 5.4 m molality) lowers the freezing point by about 37°C, protecting to -37°C. The van't Hoff factor i = 1 for ethylene glycol (it doesn't ionize).
Is this calculator free?
Yes, completely free with no signup required. All calculations run in your browser.
Is my data private?
Yes. All calculations run locally. Nothing is transmitted.
What are the Kf values for common solvents?
Water: 1.853°C·kg/mol. Benzene: 5.12. Cyclohexane: 20.2. Acetic acid: 3.9. Camphor: 40 (used for high-precision molecular weight determination). Higher Kf values give more measurable freezing point changes.