This boiling point elevation calculator applies ΔTb = i · Kb · m: how much a solute raises a solvent’s boiling point, from molality, the solvent’s ebullioscopic constant and the van ‘t Hoff factor.

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Dissolved Particles Make Solvents Harder to Boil

The cooling-side twin is our Freezing Point Depression Calculator; molality itself is our Molality Calculator. Part of our Chemistry Calculators collection.

Worked Examples (Verified)

  • 0.5 m NaCl in water (defaults): ΔT = 2 × 0.512 × 0.5 = 0.512 °C → boils at 100.51 °C — pasta-water salt (~0.1 m) buys a homeopathic 0.1 °C; salt goes in for flavor, not physics
  • 1 m sucrose in water: i = 1 → ΔT = 0.512 °C — half the salt effect at double the molality, because sugar doesn’t split
  • Radiator coolant exploits the same law from the other manual: ethylene glycol solutions raise the boiling ceiling (and lower the freezing floor) — one solute, both colligative directions, which is why antifreeze is also “anti-boil”

Colligative Discipline

  • Molality, not molarity: boiling changes the volume, so the temperature-proof mol/kg is the formula’s native unit.
  • Measured elevations historically determined unknown molar masses — weigh solute, measure ΔT, solve m = ΔT/(iKb), back out moles and hence g/mol.
  • Kb values are solvent properties (water 0.512, benzene 2.53, CCl₄ 5.02, acetic acid 3.07 °C/m); camphor’s enormous Kf (≈ 37.7 °C/m) made it the classic molar-mass solvent on the freezing side.
  • Volatile solutes break the model: the law assumes the solute stays in the pot (non-volatile) while only solvent boils off.

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Frequently Asked Questions

How do you calculate boiling point elevation?

ΔTb = i × Kb × m — van ‘t Hoff factor × solvent constant × molality. Add ΔTb to the pure solvent’s boiling point. Example: 0.5 m NaCl in water: 2 × 0.512 × 0.5 = 0.512 °C elevation, boiling at 100.51 °C. This calculator does it for common solvents.

What is the van ‘t Hoff factor?

The number of particles one formula unit yields in solution: ≈1 for molecular solutes (sucrose, glucose), ≈2 for NaCl and other 1:1 salts, ≈3 for CaCl₂ or Na₂SO₄. Measured i runs a bit lower than the ideal integers due to ion pairing, especially as concentration rises.

Does salting pasta water make it boil hotter?

Barely: typical pasta salting is ~0.1–0.2 molal NaCl → ΔT ≈ 0.1–0.2 °C. Real, measurable with a good thermometer, irrelevant to cooking time. (Salt does matter for flavor and slightly for starch behavior — just not via boiling point.)

Why molality instead of molarity here?

Colligative formulas count solute per amount of solvent, and molality (mol per kg solvent) doesn’t drift with temperature or boiling, while molarity (per litre of solution) does. Near a boiling point, volumes lie; kilograms don’t.

What is Kb for water?

0.512 °C/m (0.512 °C·kg/mol). It’s small — water needs a full molal of particles for half a degree — which is why freezing-point work (Kf 1.86) historically gave more measurable signals, and camphor (Kf ≈ 37.7) more still.

Is this boiling point elevation calculator free?

Yes — free, instant, no sign-up.