Freezing Point Depression Calculator
Enter molality, the van ‘t Hoff factor and the solvent to get the freezing point depression.
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Freezing Point Depression Calculator by TheCalcTools
How the Freezing Point Depression Calculator works
Dissolved particles change a solvent’s freezing point in proportion to their molality. The van ‘t Hoff factor i counts particles per formula unit: ionic salts split into ions.
Real solutions of salts often have a slightly smaller effective i than the ideal number of ions because ions pair up.
The formula
Worked example
Using the default values shown in the calculator:
| Solvent | Water (K = 1.86 °C·kg/mol) |
|---|---|
| Your K value (°C·kg/mol) | 1.86 |
| Molality (mol/kg) | 1 |
| Van 't Hoff factor i | 2 |
| Pure solvent freezing point (°C) | 0 |
- 1 mol/kg NaCl (i = 2) in water: ΔTf = 2 × 1.86 × 1 = 3.720 °C.
- New freezing point: -3.720 °C.
Result:
| ΔTf (°C) | 3.720 |
|---|---|
| New freezing point (°C) | -3.720 |
Frequently asked questions
Why do we salt roads and pasta water?
Salt lowers the freezing point of water, so ice melts at colder temperatures. In pasta water the boiling-point rise is tiny, a fraction of a degree.
Sources and further reading
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