Boiling Point Elevation Calculator
Enter the van 't Hoff factor, the ebullioscopic constant, and the molality to find how much higher a solution boils than the pure solvent.
A colligative property
The boiling point elevation depends only on how many particles dissolve, so the calculator returns ΔTb = i × Kb × m in kelvin straight away.
What is boiling point elevation?
Why salt water boils hotter
The boiling point elevation calculator shows how much higher a solution boils than the pure solvent when a non-volatile solute is dissolved in it. Salt water boils above 100 °C, and antifreeze raises the boiling point of an engine's coolant — both are the same effect. It is a colligative property, which means it depends on the number of dissolved particles, not on their chemical identity. Dissolving sugar, salt, or any other solute lowers the solvent's vapour pressure, so the liquid must reach a higher temperature before its vapour pressure matches the surrounding air and it boils.
Enter the van 't Hoff factor, the ebullioscopic constant, and the molality to get the boiling point elevation in kelvin instantly.
The boiling point elevation is the van 't Hoff factor times the ebullioscopic constant times the molality. The van 't Hoff factor (i) counts how many particles each solute unit splits into — 1 for sugar, 2 for NaCl, 3 for CaCl₂. The ebullioscopic constant (Kb) is a property of the solvent, and the molality (m) is moles of solute per kilogram of solvent.
ΔTb = i × Kb × mTake 1 molal table salt (NaCl) dissolved in water. NaCl splits into two ions, so i = 2; water's constant is Kb = 0.512 K·kg/mol; and the molality is m = 1 mol/kg. Multiply them together: 2 × 0.512 × 1 = 1.024 K. The water now boils at roughly 101.024 °C instead of 100 °C. Because i appears as a direct multiplier, an electrolyte that releases more ions elevates the boiling point proportionally more than a non-electrolyte at the same molality.
The formula is a clean linear relationship, but a few assumptions sit behind it.
Dilute solutions and full dissociation
ΔTb = i × Kb × m assumes a dilute solution with a non-volatile solute and that the van 't Hoff factor matches ideal behaviour. In concentrated or strongly ionic solutions, ions pair up and the effective factor falls below the ideal 2 or 3, so the real elevation is a little smaller than predicted. Always use molality rather than molarity, and pick the Kb that belongs to your solvent — using water's 0.512 K·kg/mol for a different liquid gives the wrong answer.