Boiling Point Elevation Calculator
Calculate how much the boiling point of a liquid increases when a solute is dissolved.
Uses the colligative property formula ΔTb = Kb × m.
Boiling point elevation is a colligative property — a property of a solution that depends on the number of dissolved particles, not their identity. When a non-volatile solute (such as salt or sugar) is dissolved in a solvent, the boiling point of the solution is higher than that of the pure solvent.
The formula: ΔTb = Kb × m × i
Where:
- ΔTb = Boiling point elevation (in Kelvin or °C — same magnitude)
- Kb = Ebullioscopic constant (boiling point elevation constant) of the solvent
- m = Molality of the solution (moles of solute per kilogram of solvent)
- i = Van’t Hoff factor (number of particles the solute dissociates into)
Molality formula: m = moles of solute / kilograms of solvent = (mass of solute / molar mass of solute) / mass of solvent (in kg)
Van’t Hoff factor (i):
- For non-electrolytes (sugar, glucose, urea): i = 1 (no dissociation)
- For NaCl (sodium chloride): i = 2 (Na⁺ and Cl⁻)
- For CaCl₂ (calcium chloride): i = 3 (Ca²⁺ and 2 Cl⁻)
- For MgSO₄: i ≈ 1 (ion pairing makes it behave almost like a non-electrolyte)
Kb values for common solvents:
| Solvent | Normal boiling point | Kb (°C·kg/mol) |
|---|---|---|
| Water | 100°C (212°F) | 0.512 |
| Benzene | 80.1°C (176°F) | 2.53 |
| Cyclohexane | 80.7°C (177°F) | 2.79 |
| Acetic acid | 118.1°C (244°F) | 3.07 |
| Chloroform | 61.2°C (142°F) | 3.63 |
| Ethanol | 78.4°C (173°F) | 1.19 |
Practical example — Salted pasta water: Adding 10g of NaCl (molar mass 58.44 g/mol) to 1 liter of water (1 kg):
- Moles of NaCl = 10 / 58.44 = 0.171 mol
- Molality = 0.171 mol / 1 kg = 0.171 mol/kg
- ΔTb = 0.512 × 0.171 × 2 = 0.175°C
Result: Salted pasta water boils at about 100.17°C — a negligible difference. Culinary claims that salting water “makes it boil faster” are incorrect; in fact, adding salt slightly raises the boiling point.