🌡️ Boiling Point Elevation Calculator
Find how much a solute raises the boiling point: ΔTb = i·Kb·m, or solve for molality, i, or the ebullioscopic constant.
Boiling-point rise ΔTb
0.512 °C
Boiling-point elevation: ΔTb = i·Kb·m. Water Kb = 0.512 °C·kg/mol. i = van’t Hoff factor, m = molality. 🔒 Computed in your browser.
How the boiling point elevation calculator works
Boiling-point elevation is a colligative property: ΔTb = i·Kb·m, where i is the van’t Hoff factor, Kb the ebullioscopic constant (0.512 °C·kg/mol for water), and m the molality. Enter any three and the tool solves for the fourth. Rearranged, the molality is m = ΔTb ÷ (i·Kb), and the solution’s boiling point is the pure solvent’s plus ΔTb, for water, 100 °C + ΔTb.
The companion to freezing-point depression. Add ΔTb to the pure solvent’s boiling point (100 °C for water) to get the solution’s boiling point.
Frequently asked questions
What is boiling point elevation?
The rise in a solvent’s boiling point when a solute is dissolved. Like freezing-point depression, it depends on the number of particles: ΔTb = i·Kb·m.
What is Kb for water?
The ebullioscopic constant of water is 0.512 °C·kg/mol. Enter a different Kb for other solvents.
How do I find the new boiling point?
Add ΔTb to the pure solvent’s boiling point. For water that is 100 °C + ΔTb.
What is the van’t Hoff factor here?
The same i as in freezing-point depression, the number of particles per formula unit (NaCl ≈ 2, sugar = 1).
Why is boiling-point elevation smaller than freezing-point depression?
Because Kb (0.512) is smaller than Kf (1.86) for water, the same molality raises the boiling point far less than it lowers the freezing point.
What is the boiling point of 1 m NaCl in water?
ΔTb = i·Kb·m = 2 × 0.512 × 1 = 1.02 °C, so the solution boils at about 101.0 °C. NaCl gives i ≈ 2 because it splits into Na⁺ and Cl⁻.
Does salting pasta water make it boil faster?
No, dissolved salt raises the boiling point slightly (a teaspoon per litre barely moves it), so the water ends up marginally hotter but takes a little longer, not less time, to boil. The salt is for flavour, not speed.