Compute freezing point depression from molality, van't Hoff factor, and constants quickly. Switch units, view steps, and download clean reports for records anytime anywhere.
Freezing point depression is a colligative property that depends on the number of dissolved particles:
Here, i is the van't Hoff factor, Kf is the cryoscopic constant, and m is molality.
| Solvent | Kf (°C·kg/mol) | Tf₀ (°C) | i | m (mol/kg) | ΔTf (°C) | Tf(solution) (°C) |
|---|---|---|---|---|---|---|
| Water | 1.86 | 0.00 | 2.00 | 1.000000 | 3.72 | -3.72 |
| Benzene | 5.12 | 5.50 | 1.00 | 0.250000 | 1.28 | 4.22 |
| Custom solvent | 3.50 | -10.00 | 1.50 | 0.800000 | 4.20 | -14.20 |
Values above are illustrative for learning and quick checks.
Professional article
Freezing point depression explains why adding solute lowers a solvent’s freezing temperature. It supports laboratory formulation, antifreeze selection, food processing, and cryopreservation screening. Because it is colligative, the effect depends primarily on the number of dissolved particles, not their identity, when solutions remain sufficiently dilute.
The calculator applies ΔTf = iKfm and Tf,solution = Tf,0 − ΔTf. Here, m is molality (mol/kg), Kf is the cryoscopic constant of the solvent, and i estimates particle multiplication from dissociation or association.
Solvents differ strongly in sensitivity. Water has Kf ≈ 1.86 °C·kg/mol, so a 1 molal non‑electrolyte shifts freezing by about 1.86 °C. Some organic solvents have higher Kf, producing larger shifts at the same molality. Always match constants to the correct solvent and purity grade.
For ideal non‑electrolytes, i ≈ 1. Strong electrolytes can approach integer values based on ion count (NaCl ~2, CaCl2 ~3), but real solutions often deviate due to ion pairing, incomplete dissociation, and concentration effects. Use measured or literature‑guided values when accuracy matters.
Molality is preferred because it is mass‑based and nearly temperature independent, unlike molarity (mol/L) which changes with thermal expansion. When designing freeze protection or calibrating experiments near phase transitions, this stability reduces systematic error. If you know moles of solute and solvent mass, the tool computes molality directly.
The calculator performs the physics in °C internally, then converts results for display. Temperature differences convert as Δ°F = 1.8Δ°C, while Kelvin differences equal Celsius differences. Reporting both ΔTf and Tf,solution helps cross‑check that the solution freezing point is lower than the pure solvent.
The linear relation works best for dilute, non‑reactive solutions where activity coefficients are near one. At high concentrations, in mixed solvents, or when solutes associate, hydrate, or react, deviations can be significant. If your formulation is concentrated or ionic, consider validating with measured freezing curves or activity‑based models.
For water with i = 2 and m = 1.0, the tool gives ΔTf = 2 × 1.86 × 1.0 = 3.72 °C, so freezing shifts from 0.00 °C to −3.72 °C. This aligns with the example table and illustrates how particle count and molality control the depression magnitude.
1) What does the van’t Hoff factor represent?
It estimates how many dissolved particles are produced per formula unit. Non‑electrolytes are near 1, while electrolytes can be higher due to ion formation, depending on dissociation and concentration.
2) Why does the calculator use molality instead of molarity?
Molality is based on solvent mass, so it stays stable with temperature changes. That makes it more reliable for freezing calculations where density and volume can vary near phase transitions.
3) Can ΔTf be shown in Kelvin?
Yes. A temperature difference in Kelvin equals the same numerical difference in Celsius. The tool can display ΔTf and freezing points in Kelvin while keeping the underlying calculation consistent.
4) Why might my measured freezing point differ from the result?
Real solutions can be non‑ideal. Ion pairing, solute association, impurities, and high concentration effects change activity, causing the linear colligative model to under‑ or over‑predict the freezing point.
5) How do I choose Kf for my solvent?
Use a trusted reference value for the specific solvent and purity. Presets provide common options, and the custom mode lets you enter a value when working with less common solvents.
6) Does this work for mixtures of solvents?
Not directly. Mixtures can have composition‑dependent freezing behavior and an effective Kf that changes with ratio. For mixtures, use experimental data or a dedicated phase‑diagram model.
7) What is the quickest workflow for lab notes?
Enter solvent, i, and molality or moles and mass, then calculate. Use the CSV for spreadsheets and the PDF for notebooks so your inputs and results stay consistent across runs.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.