Boiling Point Elevation Calculator
Boiling Point Elevation (°C)
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Understanding Boiling Point Elevation
Boiling point elevation is a colligative property: adding a solute raises the boiling point of a solvent. The formula is ΔTb = i × Kb × m, where i is the van't Hoff factor (number of particles the solute dissociates into), Kb is the ebullioscopic constant, and m is molality.
For water, Kb = 0.512 °C·kg/mol. Salt (NaCl) has i = 2 (dissociates into Na⁺ and Cl⁻). So 1 molal NaCl solution boils at 100 + 2(0.512)(1) = 101.024°C. Sugar (non-electrolyte) has i = 1.
This phenomenon explains why salting pasta water slightly raises the boiling point, why antifreeze raises the boiling point of engine coolant, and why seawater boils at a slightly higher temperature than pure water.
Frequently Asked Questions
What is boiling point elevation?
The increase in a solvent's boiling point when a solute is dissolved: ΔTb = i × Kb × m. It's a colligative property depending only on particle count.
What is the van't Hoff factor?
The number of particles a solute produces in solution. NaCl → Na⁺ + Cl⁻, so i = 2. Glucose doesn't dissociate, so i = 1. CaCl₂ → Ca²⁺ + 2Cl⁻, so i = 3.
What is Kb for water?
Kb = 0.512 °C·kg/mol. Each mole of non-electrolyte solute per kg of water raises the boiling point by 0.512°C.
Does adding salt significantly raise boiling point?
Not much for cooking. A typical pinch of salt raises the boiling point by only about 0.04°C. You'd need very large amounts for a noticeable effect.