Boiling Point Elevation (Molality) Calculator
Find how much a dissolved solute raises a solvent’s boiling point from its molality, ebullioscopic constant and van’t Hoff factor.
How it works
ΔTb = i × Kb × molality · new boiling point = normal boiling point + ΔTb
Boiling point elevation is the mirror image of freezing point depression: a non-volatile solute lowers the solvent’s vapour pressure, so a higher temperature is needed to reach boiling. Like all colligative properties it depends on the number of dissolved particles, captured by the van’t Hoff factor i, and on the solvent’s ebullioscopic constant Kb.
Worked example
Dissolving a non-electrolyte to 0.5 mol/kg in water (Kb = 0.512, i = 1): ΔTb = 1 × 0.512 × 0.5 = 0.256 °C. Water boils at 100.256 °C instead of 100 °C.
Sources: Boiling-point elevation — Wikipedia
Frequently asked questions
Why is boiling point elevation so much smaller than freezing point depression?
For water, Kb (0.512) is much smaller than Kf (1.86), so the same molality shifts the boiling point far less than the freezing point. That is a property of the solvent, not the solute.
Does adding salt make pasta water boil faster?
No — it actually raises the boiling point slightly, so the water must get a touch hotter before it boils. The effect from a normal pinch of salt is tiny, well under a degree.
Which concentration unit is required?
Molality, moles of solute per kilogram of solvent. It is temperature-independent, which matters because the calculation spans the range up to boiling.
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This calculator is for educational purposes. Double-check important results before acting on them.