Freezing Point Depression Calculator
Calculate how much a dissolved solute lowers the freezing point of a solvent.
About Freezing Point Depression Calculator
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.
Formula
Freezing Point Depression
ΔT_f = i K_f b
- K_f
- Cryoscopic constant, 1.86 K·kg/mol for water
- i
- Number of particles per formula unit
Worked example
With the default values below, Freezing Point Depression Calculator returns Freezing Point Depression of 7.4400. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Molality of the solutionminimum 0 mol/kg
- 2 mol/kg
- Cryoscopic constantminimum 0 K kg/mol
- 1.86 K kg/mol
- Van’t Hoff factoraccepts 1–10
- 2
- Normal freezing pointaccepts -100–200 C
- 0 C
Results
- Freezing Point Depression
- 7.4400 K
- New Freezing Point
- -7.440 C
- Effective Particle Molality
- 4.0000 mol/kg
- Molality Needed for a Ten-Degree Drop
- 2.6882 mol/kg
- Interpretation
- Moderate depression
Step by step
- 1Values used
- 2Freezing Point Depression
- 3Freezing Point Depression= 7.4400 K
- 4New Freezing Point= -7.440 C
- 5Effective Particle Molality= 4.0000 mol/kg
- 6Molality Needed for a Ten-Degree Drop= 2.6882 mol/kg
- 7Interpretation= Moderate depression
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Freezing Point Depression calculated?
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.
Why does Freezing Point Depression matter?
Road salt works down to about −20 °C, beyond which the required concentration exceeds solubility and other de-icers are needed.
What values do I need to enter?
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.