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Solution Freezing Point, Molality & Particle Factor

Estimate freezing-point depression for a dilute solution using solvent presets or a custom cryoscopic constant and particle factor.

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

For water with Kf = 1.86 K·kg/mol, molality 1 mol/kg and i = 2, the ideal freezing point is −3.72°C.

Tf,solution = Tf,solvent − i Kf m

Worked example

Enter these known values and leave the other values blank.

Molality
1 mol /kg
van't Hoff factor (i)
2
Freezing point depression constant
1.86 °C kg/mol
Freezing point of pure solvent
0 °C
Freezing point of solution
-3.72 °C

Assumptions and limitations

  • This dilute-solution approximation uses molality in moles of solute per kilogram of solvent, not per litre of solution.
  • The positive van’t Hoff factor describes effective dissolved particles. Ideal dissociation counts can differ from measured values. Solvent presets are rounded reference values; custom values are supported.
  • Zero molality gives the pure-solvent freezing point. Temperatures below absolute zero are rejected. The model is not a phase diagram or antifreeze product rating.
  • Acetic acid uses a rounded 16.5°C pure-solvent freezing reference based on the NIST average 289.6 ± 0.5 K; the uncertainty is not propagated.

Common questions

What assumptions matter for this calculation?

This dilute-solution approximation uses molality in moles of solute per kilogram of solvent, not per litre of solution.

References

Bookify requires a positive effective van’t Hoff factor and labels the cryoscopic constant with its full dimensions. The acetic-acid preset uses 16.5°C, rounded from the NIST fusion-temperature average, instead of the duplicated nitrobenzene value.

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