How this calculator works
Dissolved particles lower the freezing temperature when the solid phase excludes the solute. Multiply the cryoscopic constant by solute molality and the effective particle factor, then subtract the change from the pure-solvent freezing point. Molality means moles per kilogram of solvent, not per litre of solution. Presets are rounded reference values near one atmosphere. Custom data lets you use a protocol-specific constant. These dilute-solution equations do not describe concentrated mixtures or eutectics.
Formula
DeltaTf = i Kf m; Tsolution = Tpure - DeltaTf. m is mol/kg solvent; K is K kg/mol. A temperature difference of 1 K equals 1 Celsius degree.
Worked example
With water Kf = 1.86 K kg/mol, 1 mol/kg nonelectrolyte lowers the freezing point by 1.86 K, to -1.86 C. A 0.5 mol/kg solute with i = 2 gives the same change.
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Frequently asked questions
Is molality the same as molarity?
No. Molality uses kilograms of solvent; molarity uses litres of final solution.
How should I choose the van't Hoff factor?
Use an experimentally appropriate value; ideal complete dissociation is only an approximation.
Can I solve a solvent constant?
Yes. Select solvent constant and provide a measured temperature-change magnitude, molality and particle factor.