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Boiling Point Elevation Calculator

Find how much a solute raises the boiling point.

Result

101.02 °C
1.02 °C

How it is calculated

Dissolving a non-volatile solute raises a solvent's boiling point by ΔTb = i × Kb × m. Here Kb is the solvent's ebullioscopic constant in °C·kg/mol (0.512 for water), m is the molality in mol of solute per kg of solvent, and i is the van 't Hoff factor, the number of particles each formula unit gives (1 for sugar, about 2 for NaCl). If i is left empty or not positive it is taken as 1. The tool also shows the new boiling point as 100 + ΔTb, so that figure is meaningful only for water at normal pressure. Real solutions deviate at high concentration.

Worked example

One mole of table salt per kilogram of water: Kb = 0.512, m = 1, i = 2 because NaCl splits into Na⁺ and Cl⁻. Rise: 2 × 0.512 × 1 = 1.02 °C. New boiling point: 100 + 1.02 = 101.02 °C. With i = 1 (sugar) the rise would be only 0.51 °C.

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Common mistakes

  • Using molarity (mol per litre of solution) instead of molality (mol per kg of solvent).
  • Forgetting the van 't Hoff factor for salts. Ionic compounds raise the boiling point about i times more than molecular ones.
  • Reading the "boiling point" line for a solvent other than water. It simply adds the rise to 100 °C, so use the rise alone for other solvents.
  • Entering the amount of salt in grams. Convert to moles using the molar mass and divide by kilograms of solvent first.
  • Expecting a kitchen-size pinch of salt to change the boiling point noticeably. The effect is small at everyday concentrations.

Sources

About this calculator

This calculator computes boiling point elevation using ΔTb = i·Kb·m, where i is the van't Hoff factor (number of particles a solute dissociates into), Kb is the ebullioscopic constant of the solvent (0.512 °C·kg/mol for water), and m is the solution's molality.

Chemistry students and lab technicians use it to predict how much dissolving a solute — like salt in water — raises the boiling point above the pure solvent's, a colligative property that depends only on particle count, not solute identity.

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Comments (1)

  • Editorial team

    To get a sense of scale: 10 g of table salt in 1 kg of water is about 0.171 mol, so with i = 2 the rise is roughly 0.18 °C. That is why salted pasta water boils at nearly the same temperature as plain water. The second output line simply adds the rise to 100, so for another solvent use the rise alone. Which solvent and Kb value are you using?

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