Freezing Point Depression Calculator
Calculate freezing point depression from molality, the cryoscopic constant, and the van ’t Hoff factor.
Freezing Point Depression (ΔTf)
Freezing Point Depression ΔTf
New Freezing Point
Calculation Steps
What Is Freezing Point Depression?
Freezing point depression is a colligative property: dissolving a non-volatile solute in a solvent lowers the temperature at which the solution freezes. The size of the drop depends only on how many solute particles are present, not on their chemical identity. This is why salt is spread on icy roads and why antifreeze keeps a car’s coolant liquid below 0 °C.
The Freezing Point Depression Formula
The freezing point depression is calculated from the molality of the solution, the cryoscopic constant of the solvent, and the van ’t Hoff factor:
ΔTf = i × Kf × m
New freezing point = Tf(solvent) − ΔTf
- • ΔTf = freezing point depression (°C)
- • i = van ’t Hoff factor (number of particles per formula unit)
- • Kf = cryoscopic constant of the solvent (°C·kg/mol)
- • m = molality of the solution (mol/kg)
Cryoscopic Constants (Kf)
The cryoscopic constant Kf depends on the solvent. Water’s value of 1.86 °C·kg/mol is the most common, but other solvents differ significantly:
| Solvent | Kf (°C·kg/mol) |
|---|---|
| Water | 1.86 |
| Benzene | 5.12 |
| Acetic acid | 3.90 |
| Camphor | 40.0 |
Note: This calculator assumes an ideal dilute solution with a non-volatile solute. The van ’t Hoff factor i equals 1 for non-electrolytes (such as sugar), 2 for fully dissociating salts like NaCl, and 3 for salts like CaCl₂. At higher concentrations, ion pairing reduces the effective value of i, so real measurements may differ slightly from these predictions.