Colligative properties

Colligative properties are solution properties determined primarily by the number concentration of dissolved particles, rather than their chemical identity. They arise from the effect of solute particles on the solvent’s chemical potential.

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. It quantifies the vapor-pressure lowering that underlies several colligative effects.
Mole fraction: The ratio of a component’s amount of substance to the total amount of all components in a mixture. Ideal vapor-pressure relations use solvent mole fraction to connect composition with vapor pressure.
Cryoscopy: A method that determines a solution’s properties by measuring its freezing-point depression. The freezing-point shift can reveal the concentration or molar mass of a dissolved substance.
Constitutive properties: Properties whose values depend on the chemical identity or structure of a substance, not merely the number of dissolved particles. They contrast with colligative properties, which chiefly track particle concentration.
Vapor-pressure lowering: The reduction in a solvent’s vapor pressure when a nonvolatile solute is dissolved in it. It is the direct vapor-phase consequence of fewer solvent molecules at the liquid surface.
Molality: The amount of solute, in moles, per kilogram of solvent. Freezing-point and boiling-point formulas commonly express particle concentration using molality.
Ebullioscopy: A method for studying solutions by measuring their boiling-point elevation. The boiling-point change can be used to estimate solute concentration or molar mass.
Osmolality: The number of osmoles of solute particles per kilogram of solvent. It counts effective dissolved particles directly, while colligative formulas may require corrections for nonideality.
Boiling-point elevation: The increase in a solvent’s boiling temperature caused by dissolving a nonvolatile solute. The solution must be heated further for its vapor pressure to reach the external pressure.
Van 't Hoff factor: The ratio of the actual number of dissolved particles to the number expected from the amount of solute added. It corrects particle-count predictions when solutes dissociate or associate.

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