Boiling Point Elevation Calculator

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:

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.