Boiling Point Elevation Calculator
Determine the boiling point elevation caused by a dissolved solute using the colligative property relationship.
Water at 1 atm boils at 100 C.
Water has Kb near 0.512 C kg per mol.
For electrolytes, use the expected dissociation count.
Boiling point elevation
0.77 C
Solution boiling point
100.77 C
How to Use This Calculator
Gather solvent data
Record the pure solvent boiling point and its ebullioscopic constant.
Measure solute amount
Compute or measure the solution molality (moles solute per kilogram solvent).
Identify van't Hoff factor
Estimate the number of particles produced per solute formula unit (use 1 for non-electrolytes).
Review elevation and new boiling point
The calculator multiplies i, Kb, and m to give DeltaTb and adds it to the pure solvent boiling point.
Formula
DeltaTb = i * Kb * m
Solution boiling point Tb(solution) = Tb(solvent) + DeltaTb. Units: Kb in C kg per mol, m in mol per kg, i dimensionless.
Example
For a 1.5 molal sucrose solution in water: DeltaTb = 1 * 0.512 * 1.5 = 0.768 C, so boiling point becomes 100.768 C.
Full Description
Boiling point elevation is a colligative property that depends on the number of dissolved particles, not their identity. Dissolved solutes lower vapor pressure, requiring a higher temperature to reach boiling.
The magnitude scales with the ebullioscopic constant, the solution molality, and the van't Hoff factor. This calculator assumes dilution where the linear relationship holds.
Frequently Asked Questions
Why use molality instead of molarity?
Molality is mass based and does not change with temperature, making it appropriate for boiling point calculations.
How do electrolytes affect the result?
Electrolytes dissociate into multiple ions, increasing the van't Hoff factor and thus the boiling point elevation.
Can I use this for concentrated solutions?
The linear relationship holds best for dilute solutions. Highly concentrated solutions require activity coefficients.
Where do I find Kb values?
Chemistry handbooks list ebullioscopic constants for common solvents and temperatures.
Does pressure matter?
The ebullioscopic equation assumes constant pressure. Large pressure changes need additional corrections.