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Boiling Point Elevation Calculator

Find how much a solute raises the boiling point.

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.

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. Enter the molality, van't Hoff factor, and Kb to get the elevation and new boiling point.

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