Boiling Point Elevation Calculator
Calculate how much the boiling point of a solvent increases when a solute is dissolved in it. Uses the colligative property formula ΔTb = i × Kb × m, where i is the van't Hoff factor, Kb is the ebullioscopic constant, and m is molality.
Boiling point elevation is a colligative property, meaning it depends on the number of solute particles in solution, not their identity. When a non-volatile solute is dissolved in a solvent, the boiling point of the solution is higher than that of the pure solvent.
The Formula: ΔTb = i × Kb × m
- i = van't Hoff factor (number of particles per formula unit). For non-electrolytes like sugar, i = 1. For NaCl, i = 2 (Na⁺ + Cl⁻). For CaCl₂, i = 3.
- Kb = ebullioscopic constant, a property of the solvent. Water has Kb = 0.512 °C·kg/mol.
- m = molality, moles of solute per kilogram of solvent.
Why It Happens
Adding solute lowers the vapor pressure of the solvent (Raoult's law). Since the liquid must reach a higher temperature to achieve a vapor pressure equal to atmospheric pressure, the boiling point increases. The elevation is directly proportional to the concentration of solute particles.
Practical Applications
Antifreeze mixtures (ethylene glycol in water) raise the boiling point and lower the freezing point of engine coolant. Cooking with salted water results in a slightly higher boiling point, though the effect is small at typical cooking concentrations.