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Boiling point elevation with a partially dissociated solute: finding the mole percent dissociated

Type the data from the question into the instrument panel, press Run experiment, and watch the bench boil the pure solvent, dissolve B, fall short of your measurement, and then break B apart until the flask matches - the mole percent dissociated is the outcome of the run, not a printed calculation.

Sub-topics covered

• Elevation of boiling point
• Ebullioscopic constant from enthalpy of vaporisation
• van't Hoff factor from dissociation stoichiometry
• Molality from a mass percentage
• Degree of dissociation
• Cancellation of an unknown molar mass

What it teaches

• Kb is not a table value here - it follows from the solvent's boiling point and enthalpy of vaporisation
• Quoting the enthalpy of vaporisation as 10R makes the gas constant cancel out of Kb entirely
• Kb is proportional to the solvent's molar mass and the molality is inversely proportional to it, so their product is independent of the solvent
• A colligative property counts particles, so B giving 2C + 2D contributes four particles for every one that dissociates
• i = 1 + 3(alpha) for B into 2C + 2D, bounded by 1 and 4
• The rise in boiling point is measured from the pure solvent, not the boiling point itself

Simulation ID

• ADV-2026-P2-CHE-Q12 · revision 2

See this simulation in the library →  ·  open the simulation file on its own