About the Freezing Point Depression Calculator

Freezing point depression is a colligative property: dissolving a solute lowers the freezing point of a solvent in proportion to the number of dissolved particles, regardless of what those particles are. The governing equation is ΔTf = i · Kf · m, where m is molality (moles of solute per kilogram of solvent), Kf is the solvent's cryoscopic constant, and i is the van't Hoff factor counting particles per formula unit.

Why it matters

It is why salt melts ice on roads (brine freezes near −6 °C), why antifreeze works in car radiators, and why chemists can determine molar masses by measuring the freezing point of a solution. Water's Kf of 1.86 °C·kg/mol means a 1 molal solution of any non-electrolyte freezes at −1.86 °C — and with a dissociating salt like NaCl (i = 2) the depression doubles.