Boiling Point Elevation Calculator

Calculate how much a dissolved solute raises a solvent's boiling point using the colligative property formula ΔTb = i · Kb · m. Enter your solvent, van't Hoff factor (i), and molality (m) — or compute molality from solute mass, molar mass, and solvent mass. Get the boiling point elevation (ΔTb) and the new boiling point of the solution instantly. Also try the Heat Loss Calculator.

Select a solvent to auto-fill its ebullioscopic constant and normal boiling point.

°C·kg/mol

Auto-filled from solvent preset. Override for custom solvents.

°C

Normal boiling point of the pure solvent at 1 atm.

Select solute type to auto-fill the van't Hoff factor, or choose Custom.

Number of particles the solute dissociates into. 1 for non-electrolytes.

Enter Molality As *

mol/kg

Moles of solute per kilogram of solvent.

g

Mass of the dissolved solute in grams.

g/mol

Molar mass of the solute (e.g. NaCl = 58.44 g/mol).

g

Mass of the pure solvent in grams.

Results

Boiling Point Elevation (ΔTb)

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New Boiling Point of Solution

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Molality Used (m)

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Normal Boiling Point of Solvent

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Frequently Asked Questions

What is boiling point elevation?

Boiling point elevation is the rise in the boiling point of a solvent when a non-volatile solute is dissolved in it. It is a colligative property, meaning it depends on the number of dissolved particles rather than their chemical identity. Adding solute lowers the solvent's vapor pressure, so a higher temperature is needed to reach the boiling point. See also our calculate Charles' Law.

What formula is used to calculate boiling point elevation?

The formula is ΔTb = i · Kb · m, where ΔTb is the boiling point elevation, i is the van't Hoff factor (number of particles the solute dissociates into), Kb is the ebullioscopic constant of the solvent, and m is the molality of the solution in mol/kg.

What is the ebullioscopic constant of water?

The ebullioscopic constant (Kb) of water is 0.512 °C·kg/mol. This means that dissolving 1 mole of a non-dissociating solute in 1 kg of water raises the boiling point by 0.512 °C.

What is the ebullioscopic constant of benzene?

Benzene has an ebullioscopic constant (Kb) of 2.53 °C·kg/mol, which is significantly higher than water. Its normal boiling point is 80.10 °C, making it a common solvent used in colligative property experiments. You might also find our Junction Temperature — Power MOSFET Thermal useful.

What is the van't Hoff factor (i)?

The van't Hoff factor (i) represents the number of particles a solute produces when dissolved. Non-electrolytes like sugar have i = 1, while ionic compounds dissociate: NaCl gives i = 2, CaCl₂ gives i = 3, and AlCl₃ gives i = 4 under ideal conditions.

How do I calculate molality from mass?

Molality (m) = (mass of solute in grams / molar mass of solute) / (mass of solvent in kilograms). For example, dissolving 58.44 g of NaCl (molar mass 58.44 g/mol) in 1000 g of water gives a molality of 1.0 mol/kg.

Does boiling point elevation depend on the type of solute?

It depends on the number of solute particles, not their chemical nature. Two different solutes at the same molality and with the same van't Hoff factor will produce identical boiling point elevations in the same solvent. This is why it's called a colligative property.

Why does adding salt to water raise its boiling point?

Salt (NaCl) dissociates into Na⁺ and Cl⁻ ions when dissolved, doubling the number of particles in solution (i = 2). These extra particles lower the vapor pressure of water, meaning more heat energy is required to bring the solution to a boil compared to pure water.