Calculates how much a dissolved solute lowers a solvent’s freezing point — the same colligative-property principle behind road salt melting ice.
How it works
The number of particles the solute dissociates into is multiplied by the solvent’s cryoscopic constant and the solution’s molality.
What this does not include
This does not include the opposite effect on boiling point — for that, use this site’s boiling point elevation calculator instead, which uses the same underlying principle applied to the other phase transition.
How to use this calculator
- Enter the Van’t Hoff factor, the solvent’s cryoscopic constant (water’s value is pre-filled), and the molality.
A worked example
A solute with van’t Hoff factor 2 (like a salt that dissociates into two ions), Kf = 1.86, molality 0.5: freezing point depression = i×Kf×m = 2×1.86×0.5 = 1.86°C.
A non-dissociating solute (i=1), Kf = 1.86, molality 1: depression is also 1.86°C.
What the variables mean
| Variable | Meaning |
|---|---|
| i (van’t Hoff factor) | Number of particles the solute dissociates into |
| Kf | The solvent’s freezing point depression constant |
| Molality | Moles of solute per kg of solvent |
Edge cases worth knowing
A dissociating solute like salt depresses the freezing point more than a non-dissociating one at the same molality — each ion it splits into contributes separately, which is exactly why road salt (which dissociates into two ions) works better than an equal molar amount of sugar (which doesn’t dissociate at all).
A negative van’t Hoff factor has no physical meaning, so the calculator declines to show a result for one.
Frequently asked questions
Why does salting roads melt ice?
Dissolved salt lowers the freezing point of the water on the road below the ambient temperature, so ice that would normally stay frozen instead melts.
Does antifreeze work the same way?
Yes — antifreeze lowers a car radiator’s freezing point using the same colligative-property principle, just with a different solute (typically ethylene glycol) than table salt.
Why is the cryoscopic constant different from the ebullioscopic constant?
They’re both properties of the solvent, but they describe different physical processes (freezing vs. boiling) and are measured independently — for water they happen to be different numbers (1.86 vs. 0.512).
