Boiling-point elevation

Boiling-point elevation is the rise in a solvent’s boiling temperature when a nonvolatile solute is dissolved in it. For dilute solutions, the increase depends on solute-particle concentration rather than chemical identity.

Raoult’s law: A relation stating that a component’s partial vapor pressure in an ideal solution equals its mole fraction times its pure vapor pressure. A nonvolatile solute lowers the solvent’s vapor pressure, the change that leads to boiling-point elevation.
Molality: A concentration unit equal to moles of solute per kilogram of solvent. The dilute-solution equation expresses boiling-point elevation using molality.
Molecular mass determination by boiling-point elevation: A method for estimating a solute’s molar mass from the boiling-point increase it produces in a solvent. A measured elevation can be converted into particle concentration and, with sample mass, molar mass.
Freezing-point depression: The lowering of a solvent’s freezing temperature when a solute is dissolved in it. It is the best-known colligative counterpart: the same particle presence shifts a phase-change temperature downward.
Vapor pressure: The pressure exerted by a vapor in equilibrium with its liquid at a given temperature. A solution must reach atmospheric pressure to boil, and the solute lowers its vapor pressure at a given temperature.
Van ’t Hoff factor: The ratio of the actual number of dissolved particles to the number of formula units dissolved. Electrolytes can produce multiple particles per formula unit, magnifying the temperature shift.
Antifreeze: A substance added to a liquid to lower its freezing point and often raise its boiling point. Ethylene glycol in engine coolant illustrates a practical use of colligative temperature shifts.
Osmotic pressure: The pressure required to prevent solvent flow across a semipermeable membrane into a more concentrated solution. It is another colligative effect, expressed as a pressure rather than a boiling-temperature shift.
Colligative properties: Solution properties that, in dilute solutions, depend chiefly on the number of dissolved particles rather than their chemical identity. Boiling-point elevation is one of this family’s particle-count-dependent effects.
Electrolyte: A substance that forms mobile ions when dissolved in a solvent or melted. Dissociation makes many electrolytes produce more solute particles than their formula-unit count suggests.

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