❄️ Freezing Point Depression Calculator
Find how much a solute lowers the freezing point: ΔTf = i·Kf·m — or solve for molality, i, or the cryoscopic constant.
Freezing-point drop ΔTf
1.86 °C
Freezing-point depression: ΔTf = i·Kf·m. Water Kf = 1.86 °C·kg/mol. i = van’t Hoff factor, m = molality. 🔒 Computed in your browser.
How the freezing point depression calculator works
Freezing-point depression is a colligative property: ΔTf = i·Kf·m, where i is the van’t Hoff factor (particles per formula unit), Kf the cryoscopic constant (1.86 °C·kg/mol for water), and m the molality. Enter any three and the tool solves for the fourth.
Why salt melts ice and antifreeze works. For ionic solutes use i = number of ions (NaCl ≈ 2, CaCl₂ ≈ 3); for molecular solutes like sugar, i = 1.
Frequently asked questions
What is freezing point depression?
The lowering of a solvent’s freezing point when a solute is dissolved in it. It depends on the number of dissolved particles, not their identity — a colligative property. ΔTf = i·Kf·m.
What is the van’t Hoff factor (i)?
The number of particles a solute splits into. NaCl gives i ≈ 2 (Na⁺ + Cl⁻), CaCl₂ ≈ 3, and non-electrolytes like glucose give i = 1.
What is Kf for water?
The cryoscopic constant of water is 1.86 °C·kg/mol. Other solvents have their own Kf, which you can enter.
How do I find the new freezing point?
Subtract ΔTf from the pure solvent’s freezing point. For water, 0 °C − ΔTf. The tool gives ΔTf; subtract it yourself.
Why does salt melt ice?
Dissolved salt depresses the freezing point below the ambient temperature, so the ice melts. More particles (higher i·m) means a larger depression.