Freezing Point Depression Calculator
Calculate the freezing point depression of a solution.
Formula first
Overview
Freezing point depression is a colligative property where the addition of a solute decreases the temperature at which a solvent solidifies. This phenomenon occurs because solute particles interfere with the solvent's ability to form an organized crystal lattice, requiring more energy to be removed from the system.
Symbols
Variables
K = Freezing Point Depression (ΔTf), i = van't Hoff Factor, K·kg/mol = Cryoscopic Constant (Kf), mol/kg = Molality
Apply it well
When To Use
When to use: Apply this equation when calculating the change in freezing point for dilute, non-volatile solutions. It assumes the solute does not enter the solid phase and the solution behaves ideally.
Why it matters: This principle is critical for industrial applications like de-icing roads and formulating automotive antifreeze. It is also used in laboratory settings to determine the molar mass of unknown substances or to calculate the degree of dissociation for electrolytes.
Avoid these traps
Common Mistakes
- Subtracting from 100 instead of 0 (for water).
- Using Molarity instead of Molality.
One free problem
Practice Problem
A solution is prepared by dissolving glucose into water. Given the molality is 2.0 m, the van't Hoff factor is 1, and the cryoscopic constant (Kf) for water is 1.86 °C/m, calculate the freezing point depression (ΔTᶠ).
Solve for: dT
Hint: Multiply the van't Hoff factor, the cryoscopic constant, and the molality together.
The full worked solution stays in the interactive walkthrough.
References
Sources
- Atkins' Physical Chemistry
- McQuarrie, Donald A., and John D. Simon. Physical Chemistry: A Molecular Approach.
- Wikipedia: Freezing-point depression
- IUPAC Gold Book: freezing-point depression
- IUPAC Gold Book: molality
- IUPAC Gold Book: cryoscopic constant
- IUPAC Gold Book: van 't Hoff factor
- Atkins' Physical Chemistry, 11th Edition