Freezing Point Depression Calculator
How far a dissolved substance lowers the freezing point of a solvent.
Results
Temperature drop
3.72000
K
Freezing point
-3.7200
°C
Molality
2.00000
mol/kg
What this tool does
Dissolved particles get in the way of the orderly arrangement a crystal needs, so the liquid has to be taken colder before it will freeze. Water's cryoscopic constant is 1.86 K·kg/mol; benzene is 5.12 and camphor a remarkable 40, which is why camphor was once used to measure molar masses this way.
Formula
ΔTf = i × Kf × b
Variables
| Symbol | Meaning | Unit |
|---|---|---|
kf | Cryoscopic constant | K·kg/mol |
bb | Molality | mol/kg |
iv | van 't Hoff factor | — |
tf | Freezing point | °C |
DT | Temperature drop | K |
TN | Freezing point | °C |
BM | Molality | mol/kg |
Worked example
- Cryoscopic constant1.86 K·kg/mol
- Molality1 mol/kg
- van 't Hoff factor2
- Freezing point0 °C
- Temperature drop3.72000 K
- Freezing point-3.7200 °C
- Molality2.00000 mol/kg
Limitations
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.
Frequently asked questions
What is the van 't Hoff factor for?
It counts how many particles each formula unit becomes in solution. Sugar dissolves as whole molecules, so its factor is 1. Table salt splits into a sodium and a chloride ion, giving 2, and calcium chloride gives 3 — which is why it is the more effective de-icer per kilogram. The effect depends on the number of particles, not on what they are.