Science & engineering
Boiling & freezing point shifts
Estimate ideal boiling-point elevation and freezing-point depression from molality.
A clear answer. Here’s how.
Uses ΔTb=iKb m and ΔTf=iKf m for an ideal dilute solution with a non-volatile solute. Adds the boiling shift and subtracts the freezing shift from the supplied pure-solvent values. Defaults illustrate water at approximately 1 atm; constants and pressure conditions are your inputs. Dissociation, association and non-ideal behaviour are not inferred. Results below absolute zero are rejected.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Formula-unit molality (mol/kg solvent)
- 0.5
- Effective particle factor i
- 1
- Solvent boiling elevation constant (K·kg/mol)
- 0.512
- Solvent freezing depression constant (K·kg/mol)
- 1.86
- Pure solvent boiling point at stated pressure (°C)
- 100
- Pure solvent freezing point at stated pressure (°C)
- 0
Example result
- Boiling-point elevation
- 0.256 K
- Freezing-point depression
- 0.93 K
- Estimated solution boiling point
- 100.256 °C
- Estimated solution freezing point
- -0.93 °C