What Is Boiling Point Elevation?
Boiling point elevation is a colligative property: dissolving a non-volatile solute in a solvent raises the temperature at which the solution boils. The size of the increase depends only on the number of dissolved particles, not their identity. This calculator computes the elevation (Δ T_b) and the resulting boiling point of the solution.
How to Use This Calculator
Enter four values: the van't Hoff factor i (1 for non-electrolytes like sugar, ~2 for NaCl, ~3 for CaCl₂), the molal boiling point elevation constant Kb for the solvent (0.512 °C·kg/mol for water), the molality of the solution (moles of solute per kilogram of solvent), and the pure solvent boiling point (100 °C for water). The tool returns Δ T_b and the new boiling point.
The Formula Explained
The governing equation is
Worked Example
Dissolve NaCl in water to a molality of 1 mol/kg. NaCl splits into Na⁺ and Cl⁻, so i ≈ 2, Kb = 0.512, m = 1.
Kb Constants and van't Hoff Factors
Boiling point elevation is a colligative property described by the equation:
where i is the van't Hoff factor (the number of dissolved particles per formula unit of solute), K_b is the ebullioscopic (molal boiling point elevation) constant of the solvent in °C·kg/mol, and m is the molality of the solution in mol/kg. The elevated boiling point of the solution is then the pure solvent's boiling point plus Δ T_b.
Ebullioscopic Constants (Kb) of Common Solvents
Each solvent has a characteristic K_b value that depends only on the solvent, not on the solute. Larger K_b values produce greater elevation per unit molality.
| Solvent | Kb (°C·kg/mol) | Normal Boiling Point (°C) |
|---|---|---|
| Water | 0.512 | 100 |
| Ethanol | 1.22 | 78.4 |
| Benzene | 2.53 | 80.1 |
| Chloroform | 3.63 | 61.2 |
| Acetic acid | 3.07 | 118 |
Typical van't Hoff Factors (i)
The van't Hoff factor reflects how many particles a solute releases when dissolved. Non-electrolytes such as sugar do not dissociate (i = 1), while ionic compounds dissociate into multiple ions, raising i. The values below are the ideal (theoretical) factors; real measured values are often slightly lower due to ion pairing.
| Solute | Dissociation | van't Hoff factor (i) |
|---|---|---|
| Sugar / glucose (non-electrolyte) | does not dissociate | 1 |
| Sodium chloride (NaCl) | Na⁺ + Cl⁻ | 2 |
| Calcium chloride (CaCl₂) | Ca²⁺ + 2 Cl⁻ | 3 |
| Potassium sulfate (K₂SO₄) | 2 K⁺ + SO₄²⁻ | 3 |
| Aluminum chloride (AlCl₃) | Al³⁺ + 3 Cl⁻ | 4 |
As a quick reference, dissolving 1 mol/kg of NaCl in water elevates the boiling point by 1.024 °C, giving a solution boiling point of about 101.024 °C.
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