Boiling Point Elevation Calculator

ΔT = i·Kb·b, with the van 't Hoff factor made explicit.

ΔT = i·Kb·b, with the van 't Hoff factor made explicit. A dissolved solute raises the boiling point in proportion to the number of particles it contributes.

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

Molality

mol/kg

Ebullioscopic constant (Kb)

0.512 for water. It is a property of the solvent.

van 't Hoff factor (i)

Particles per formula unit: 1 for sugar, 2 for NaCl, 3 for CaCl₂.

Normal boiling point

°C

Boiling point (°C)

100.512

Raised by 0.512 °C

Change in temperature0.512 °C

New boiling point100.512 °C

Molality1 mol/kg

Effective particle molality1 mol/kg

ΔT = i·K·b. The van 't Hoff factor is the part most often left at 1 by mistake: sodium chloride splits into two ions, so per mole it shifts the boiling point twice as far as sucrose does. Colligative properties count particles, not identity — which is why road salt works and why it is spread by mass rather than by chemistry.

How the Boiling Point Elevation Calculator works

A dissolved solute raises the boiling point in proportion to the number of particles it contributes. The van 't Hoff factor is the part most often left at 1 by mistake: sodium chloride splits into two ions and shifts the point twice as far per mole as sucrose does.

Also known as: ebullioscopic constant calculator · colligative properties calculator · delta t boiling point · how to calculate boiling point elevation

Where to go next

The Boiling Point Elevation question rarely arrives on its own. These are the ones that usually come with it:

Freezing Point Depression Calculator — Why road salt works, quantified.
Osmotic Pressure Calculator — Π = iMRT, and the figures are larger than you expect.
Molality Calculator — Per kilogram of solvent — not per litre of solution.
Vapor Pressure Calculator — Antoine constants are inputs, because ranges matter.

Sources

Frequently asked questions

How do I calculate boiling point elevation?

ΔT = i·Kb·b. For water Kb is 0.512 °C·kg/mol, so a 1 molal solution of a non-dissociating solute boils at 100.512 °C.

What is the van 't Hoff factor?

The number of particles a formula unit produces in solution: 1 for sugar, 2 for NaCl, 3 for CaCl₂. Colligative properties count particles, not identity.

Why does salting pasta water barely help?

Because the effect is small at culinary concentrations. A tablespoon of salt in four litres raises the boiling point by well under a tenth of a degree — the salt is for flavour.

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