Calculate how much a dissolved solute lowers the freezing point of a solvent.
Freezing point depression is about 3.6 times larger than boiling point elevation for water, because the cryoscopic constant is larger. That asymmetry is why salt is effective for de-icing but nearly useless for raising boiling temperature. Road salt works down to about −20 °C, beyond which the required concentration exceeds solubility and other de-icers are needed.
Freezing Point Depression
ΔT_f = i K_f b
ΔT_f = i K_f b Freezing point depression is about 3.6 times larger than boiling point elevation for water, because the cryoscopic constant is larger. That asymmetry is why salt is effective for de-icing but nearly useless for raising boiling temperature.
Road salt works down to about −20 °C, beyond which the required concentration exceeds solubility and other de-icers are needed.
This calculator takes 4 inputs: Molality of the solution, Cryoscopic constant, Van’t Hoff factor, Normal freezing point. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.