Boiling Point Elevation Calculator — ΔTb = Kb × m × i
Dissolving a solute always raises the boiling point of the solvent. Calculate the elevation ΔTb and the new boiling point using the colligative property formula ΔTb = Kb × m × i.
Solvent
Input method
mol/kg
Amount the boiling point rises above the pure solvent value
- 1
Molality (m)
1 - 2
Kb × m
0.512 × 1 = 0.512 - 3
Boiling point elevation ΔTb = Kb × m × i
0.512 × 2 = 1.024
How does this calculator work?
ΔTb = Kb × m × i — the boiling point elevation equals the solvent's ebullioscopic constant (Kb) times the molality (mol solute per kg solvent) times the van't Hoff factor i (1 for non-electrolytes, 2 for NaCl, 3 for CaCl₂). For water (Kb = 0.512), dissolving 1 mol/kg of NaCl (i=2) raises the boiling point by about 1.02 °C.
Formula
How this is calculated
Boiling point elevation is a colligative property — it depends only on the number of dissolved particles per kilogram of solvent, not on their identity. When a non-volatile solute is dissolved, its particles lower the vapour pressure of the solvent (Raoult's law). Because the vapour pressure is reduced, the solution must be heated to a higher temperature before it equals atmospheric pressure and boiling begins.
The formula ΔTb = Kb × m × i links three quantities: the ebullioscopic constant Kb, a fixed property of the solvent (0.512 °C·kg/mol for water; higher for solvents like camphor); the molality m, the number of moles of solute per kilogram of solvent; and the van't Hoff factor i, which accounts for ionic dissociation (NaCl dissociates into Na⁺ and Cl⁻, so i ≈ 2, effectively doubling the particle count). For non-electrolytes i = 1.
Practical applications include road salt (which raises the boiling point of the de-icing solution slightly but mainly depresses the freezing point), antifreeze in engine coolants (raises coolant boiling point above 100 °C), and industrial distillation design. The formula assumes dilute, ideal solutions and that the solute is non-volatile; concentrated solutions or volatile solutes require more sophisticated thermodynamic treatment.
Frequently asked questions
It does, but only very slightly. The typical amount of salt added to cooking water (a tablespoon in 4 litres) raises the boiling point by less than 0.1 °C — negligible for cooking purposes. The real reason to salt pasta water is flavour, not physics.
The van't Hoff factor i accounts for how many particles a formula unit produces when dissolved. Non-electrolytes like sugar give i = 1. NaCl dissociates fully into two ions so i ≈ 2. CaCl₂ gives three ions so i ≈ 3. Real values are slightly less than these ideals due to ion pairing at higher concentrations.
Molality (mol/kg) is moles of solute per kilogram of solvent; molarity (mol/L) is moles of solute per litre of solution. Molality is used in colligative property calculations because it does not change with temperature (mass is fixed), whereas volume changes with temperature.
Also known as
TG we-Calculate Editorial Team. (2026). Boiling Point Elevation Calculator — ΔTb = Kb × m × i [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/boiling-point-elevation-calculator
TG we-Calculate Editorial Team. "Boiling Point Elevation Calculator — ΔTb = Kb × m × i." TG we-Calculate. 2026. https://we-calculate.com/calculator/boiling-point-elevation-calculator.
TG we-Calculate Editorial Team, "Boiling Point Elevation Calculator — ΔTb = Kb × m × i," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/boiling-point-elevation-calculator
@misc{wecalculate_boiling_point_elevation_calculator, title = {Boiling Point Elevation Calculator — ΔTb = Kb × m × i}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/boiling-point-elevation-calculator}}, year = {2026}, note = {TG we-Calculate} }
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