Boiling Point Elevation Calculator

Calculate the boiling point elevation when a non-volatile solute is dissolved in a liquid. This is a colligative property dependent on molality and the ebullioscopic constant. Used in chemistry and food science.

Boiling point of pure solvent at 1 atm

Moles of solute per kg of solvent

Leave empty for water default (0.512 °C·kg/mol)

BOILING POINT ELEVATION: ΔTb = Kb × m Where: - ΔTb = boiling point elevation (°C) - Kb = ebullioscopic constant (°C·kg/mol) - m = molality (mol solute/kg solvent) FOR ELECTROLYTES: Use van't Hoff factor (i): ΔTb = Kb × m × i i values: - Nonelectrolytes (sugar): i = 1 - NaCl, KCl (dissociates to 2): i = 2 - CaCl₂ (dissociates to 3): i = 3 - MgSO₄ (dissociates to 2): i = 2 TYPICAL Kb VALUES: Water: 0.512 °C·kg/mol Ethanol: 1.22 Benzene: 2.53
Example 1: 1 molal sugar in water Kb = 0.512 °C·kg/mol m = 1 mol/kg ΔTb = 0.512 × 1 = 0.512°C New BP = 100 + 0.512 = 100.512°C Example 2: 0.5 molal NaCl in water NaCl dissociates, effective m = 0.5 × 2 = 1 ΔTb = 0.512 × 1 = 0.512°C New BP = 100.512°C (nearly same—salty water barely boils higher!) Example 3: 2 molal CaCl₂ Effective m = 2 × 3 = 6 ΔTb = 0.512 × 6 = 3.07°C New BP = 103.07°C

What is boiling point elevation?

Boiling point elevation (ΔTb) is the increase in a liquid's boiling point when a non-volatile solute is dissolved in it. The effect is " colligative"—depends on solute particle count (molality), not identity. For dilute solutions: ΔTb = Kb × m. Water Kb = 0.512 °C·kg/mol.

How do I calculate boiling point elevation?

Use the formula: ΔTb = Kb × m, where Kb is the ebullioscopic constant and m is molality (moles solute/kg solvent). For 1 molal NaCl in water: NaCl dissociates into 2 ions (i=2), so effective m = 2 mol/kg. ΔTb = 0.512 × 2 = 1.024°C.

What is the ebullioscopic constant?

The ebullioscopic constant (Kb) is derived from the solvent's properties: Kb = R × Tb² / (1000 × ΔHvap). Each solvent has its own Kb: water = 0.512°C·kg/mol, ethanol = 1.22, benzene = 2.53, chloroform = 3.63. Higher Kb = stronger elevation effect.

Why does salt make water boil higher?

Saltwater boiling point elevation is the "salting out" effect relevant to cooking. At the beach, seawater (very dilute!) boils at just slightly above 100°C. The effect is small because you need significant concentrations—1 M salt solution, not typical cooking. With pasta, most ions are from salt, not the pasta itself.

How accurate is this calculation?

For dilute solutions (m < 0.1 mol/kg), the formula is highly accurate. At higher concentrations, deviations occur because the linear relationship breaks down. Strong electrolytes like NaCl need van't Hoff factor i (>1). This is for ideal dilute solutions; concentrated solutions differ.

What are typical Kb values?

Common solvents: Water 0.512, Ethanol 1.22, Methanol 0.82, Acetone 1.71, Benzene 2.53, Chloroform 3.63, Carbon tetrachloride 4.88, Diethyl ether 2.02 (all °C·kg/mol). You need the correct Kb for your solvent.

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