Freezing Point Depression Calculator
Freezing point depression calculator: how far a solute lowers the freezing point, e.g. salt on roads or antifreeze.
ΔTf = i · Kf · b
How to use this calculator
- Choose the quantity you want under “Solve for”.
- Type the known values and pick their units: any combination works.
- The result updates as you type. Open “Show the steps” to see the substitution.
ΔT_f = i·K_f·b. For water K_f = 1.86 K·kg/mol.
Use i ≈ 2 for NaCl, 3 for CaCl₂ and 1 for sugars or glycol.
Formula
ΔTf = i · Kf · b
| Symbol | Quantity | Units |
|---|---|---|
| i | van 't Hoff factor | — |
| Kf | Cryoscopic constant (water 1.86) | K·kg/mol |
| b | Molality | mol/kg, mmol/kg |
| ΔTf | Freezing point drop | K, °C, °F |
Worked example
Given: i = 2 · Kf = 1.86 K·kg/mol · b = 0.5 mol/kg
ΔT = i Kf b
Result: ΔTf = 1.86 °C
Frequently asked questions
0.5 mol/kg NaCl in water?
The freezing point drops 1.86 °C, to −1.86 °C.