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.