The boiling point elevation calculator computes how much adding a solute raises the boiling point of a solvent using ΔTb = i × Kb × m. Enter the solvent, solute concentration, and van't Hoff factor to find the new boiling point.
Boiling Point Elevation (ΔTb = i·Kb·m)
NaCl=2, CaCl₂=3, glucose=1
How to Use the Boiling Point Elevation Calculator
Boiling point elevation is a colligative property — it depends only on how many solute particles are dissolved, not their identity. The formula is ΔTb = i × Kb × m.
Understanding the Variables
i is the van't Hoff factor: 1 for non-electrolytes like sugar or ethanol, 2 for strong electrolytes like NaCl that split into two ions, 3 for CaCl₂ that gives three ions. Kb is the ebullioscopic constant for the solvent (provided in the dropdown). m is molality: moles of solute per kilogram of solvent.
Example: Salt Water
Dissolve 58.44 g NaCl (1 mol) in 1 kg water: m = 1.0 mol/kg, i = 2, Kb = 0.512 °C·kg/mol. ΔTb = 2 × 0.512 × 1.0 = 1.024°C. New boiling point = 100 + 1.024 = 101.024°C. This small effect explains why salting pasta water makes negligible difference to cooking time.
Determining Molar Mass from Boiling Point
Rearrange to find solute molar mass: if you dissolve a known mass w of unknown solute and measure ΔTb, then m = ΔTb / (i × Kb), and molar mass = (w / solvent_kg) / m. This is the ebullioscopic method for molecular weight determination.
FAQ
What is boiling point elevation?
Boiling point elevation is a colligative property: adding a solute to a solvent raises its boiling point. ΔTb = i × Kb × m, where i is the van't Hoff factor (1 for non-electrolytes, 2 for NaCl, 3 for CaCl₂), Kb is the ebullioscopic constant, and m is molality (mol solute per kg solvent).
Why does salt raise the boiling point of water?
Salt dissolves into Na⁺ and Cl⁻ ions (i=2), reducing the vapor pressure of water. A higher temperature is needed to achieve the vapor pressure required for boiling. For water, Kb = 0.512°C/m. A 1 m NaCl solution boils at 100°C + 2 × 0.512 × 1 = 101.024°C — only about 1°C higher.
Is this calculator free?
Yes, completely free with no signup required. All calculations run in your browser.
Is my data private?
Yes. All calculations run locally. Nothing is transmitted.
What are the Kb values for common solvents?
Water: 0.512°C·kg/mol. Benzene: 2.53. Cyclohexane: 2.79. Chloroform: 3.63. Acetic acid: 3.07. Camphor: 5.95. Higher Kb values mean more sensitive boiling point changes per unit of solute added.