colligative properties colligative properties depend only on the number of solute particles present,...
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![Page 1: Colligative Properties Colligative properties depend only on the number of solute particles present, not on the identity of the solute particles. Among](https://reader035.vdocuments.net/reader035/viewer/2022081519/56649e245503460f94b13048/html5/thumbnails/1.jpg)
Colligative Properties
• Colligative properties depend only on the number of solute particles present, not on the identity of the solute particles.
• Among colligative properties areVapor pressure lowering Boiling point elevationMelting point depressionOsmotic pressure
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How many particles?
• All covalent molecules have 1 particle– All nonmetals– Sugar– Ethanol
• Ionic compounds you must count the # of ions.– Has a metal– NaCl=2 particles– BaCl2 =3 particles
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Vapor Pressure
As solute molecules are added to a solution, the solvent become less able to evaporate(=decreased vapor pressure).
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Boiling Point Elevation and Freezing Point Depression
Solute-solvent interactions also cause solutions to have higher boiling points and lower freezing points than the pure solvent.
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Boiling Point ElevationThe change in boiling point is proportional to the molality of the particles in solution:
Tb = Kb m p
where Kb is a constant dependent upon the solvent.
Kb for solutions of water is 0.51
P is particlesTb is added to the normal boiling point of the solvent.
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Freezing Point Depression• The change in freezing
point can be found similarly:
Tf = Kf m p
• Kf is a constant dependant upon the solvent.
• Kf for water is -1.86• Kf and Kb are found on
pg 438. Tf (a negative number) is added to the normal freezing point of the solvent.
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Colligative Properties
• Consider three beakers:– 50.0 g of ice– 50.0 g of ice + 0.15 moles NaCl– 50.0 g of ice + 0.15 moles sugar (sucrose)
• Which will have the lowest freezing point?
• Which will have the lowest boiling point?
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Colligative Properties - Osmosis
• Osmosis: the net movement of a solvent through a semipermeable membrane toward the solution with greater solute concentration.
• Movement of solvent from high solvent concentration to low solvent concentration
Osmosis plays an important role in living systems:
Membranes of red blood cells are semipermeable.