Enter the freezing point depression constant (Kf) and molality (and the van ’t Hoff factor i if applicable) to calculate the freezing point depression. To calculate the solution’s actual freezing point, you must also provide the pure solvent’s freezing point. This calculator can also evaluate Kf, molality, or ΔTf when the other values are given.

Freezing Point Calculator

Enter exactly two among Kf, Molality, and ΔT_f to compute the missing one. i defaults to 1 if blank.

Freezing Point Formula

The following equations are used to calculate the freezing point depression and the solution’s freezing point.

\Delta T_f = i \cdot K_f \cdot m \\ T_{f,\text{solution}} = T_{f,\text{pure}} - \Delta T_f
  • Where ΔTf is the freezing point depression (the magnitude of the decrease in freezing point)
  • i is the van ’t Hoff factor (≈ number of particles the solute produces in solution; often i=1 for nonelectrolytes)
  • Kf is the freezing point depression constant (cryoscopic constant) of the solvent
  • m is the molality (mol of solute per kg of solvent)
  • Tf,pure is the freezing point of the pure solvent and Tf,solution is the freezing point of the solution

To calculate the freezing point depression, multiply i, Kf, and molality. To calculate the solution’s freezing point, subtract ΔTf from the pure solvent freezing point.

Freezing Point Definition

A freezing point is the temperature at which a liquid transitions to a solid (at a given pressure).

Freezing Point Example

How to calculate a freezing point?

  1. First, determine the solvent information.

    Find the solvent’s freezing point (Tf,pure) and freezing point depression constant (Kf).

  2. Next, determine the solution information.

    Measure the molality (m) and determine the van ’t Hoff factor (i) for the solute (use i=1 for a nonelectrolyte).

  3. Finally, calculate the freezing point.

    Calculate the freezing point depression (ΔTf = i·Kf·m), then calculate the solution freezing point (Tf,solution = Tf,pure − ΔTf).

FAQ

What is a freezing point?

A freezing point is a specific temperature at which a liquid begins to transition to a solid.

What is a freezing point depression constant?

The freezing point depression constant (cryoscopic constant), Kf, is a property of the solvent that relates molality to freezing point depression (ΔTf = i·Kf·m). Its common units are °C·kg/mol (or K·kg/mol).

What is molality?

Molality is a measure of moles of solute per kilogram of solvent.