Freezing Point Depression Calculator
Calculate the freezing point depression ΔTf = Kf × m × i.
Find the new freezing point of solutions.
Useful for antifreeze, road salt, and osmometry.
Freezing Point Depression
Freezing point depression is a colligative property — it depends on the number of solute particles, not their identity.
Formula:
ΔTf = Kf × m × i
T_new = T_freeze − ΔTf
Where:
- ΔTf = freezing point depression (°C or K)
- Kf = cryoscopic constant of solvent
- m = molality (mol solute / kg solvent)
- i = van’t Hoff factor (number of particles per formula unit)
Van’t Hoff factor i:
- Non-electrolytes (glucose, sucrose): i = 1
- NaCl (→ Na⁺ + Cl⁻): ideal i = 2, actual ≈ 1.8 at typical concentrations
- CaCl₂ (→ Ca²⁺ + 2Cl⁻): ideal i = 3, actual ≈ 2.5
- MgSO₄ (→ Mg²⁺ + SO₄²⁻): ideal i = 2, actual ≈ 1.4 (ion pairing)
Kf values for common solvents:
| Solvent | Normal Freezing Point | Kf (°C·kg/mol) |
|---|---|---|
| Water | 0.00°C | 1.86 |
| Benzene | 5.50°C | 5.12 |
| Cyclohexane | 6.60°C | 20.0 |
| Camphor | 179.8°C | 37.7 |
| Acetic acid | 16.63°C | 3.90 |
Practical applications:
- Road salt (NaCl): 1 mol NaCl in 1 kg water lowers freezing point by ~3.4°C (i ≈ 1.8)
- Antifreeze (ethylene glycol): a 50/50 mix by volume protects to about −37°C
- Cryoscopy: measuring molar mass of unknown compounds by measuring ΔTf → Molar mass M = (Kf × mass_solute × 1000) / (ΔTf × mass_solvent_g)
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.