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Colligative Properties. Physical properties affected by dissolved solute particles Type of solute doesn’t matter. Number of particles does matter. Colligative means “depending on the collection”. Colligative Properties.

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colligative properties
Colligative Properties
  • Physical properties affected by dissolved solute particles
  • Type of solute doesn’t matter.
  • Number of particles does matter.
  • Colligative means “depending on the collection”
colligative properties1
Colligative Properties
  • Occur with nonvolatile solutes – ones that have little tendency to become a gas
  • 4 colligative properties:
    • Vapor pressure lowering
    • Boiling point elevation
    • Freezing point depression
    • Osmotic pressure
colligative properties2
Colligative Properties
  • Electrolytes are molecules that ionize or fall apart when in solution; nonelectrolytes do not fall apart or ionize
  • Electrolytes will have a greater impact on the 4 colligative properties
  • Why?
    • Sugar (C12H22O12) remains as one molecule when dissolved.
    • Salts like MgCl2 dissociate in water so one mole of MgCl2 actually forms 3 moles of ions.
vapor pressure lowering
Vapor Pressure Lowering
  • Pressure in a CLOSED container exerted by the particles of liquid that have escaped and become gas particles
  • Greater number of escaped particles = greater vapor pressure
  • The addition of a solute LOWERS the vapor pressure – WHY?
  • The solute molecules get in the way of the solvent molecules trying to escape at the surface of the liquid.
boiling point elevation
Boiling Point Elevation
  • A liquid boils when it’s particles can escape as a gas (or when the vapor pressure is equal to the atmospheric pressure)
  • Ex: salt in water when cooking pasta

antifreeze in radiators

  • When a solute is added, the boiling point is driven higher – WHY?
  • The solute molecules get in the way of the solvent molecules trying to escape at the surface of the liquid.
freezing point depression
Freezing Point Depression
  • A liquid freezes when its particles do not have enough energy to overcome the intermolecular forces between them.
  • So the molecules are pulled closer together and take on a defined shape.
  • When a solute is added, the freezing point is driven lower – WHY?
  • The solute molecules get in the way and make it harder for the solvent molecules to move closer and become a solid
  • Ex: salt & sand on icy roads

ethylene glycol on icy airplanes

calculating b p elevation and f p depression
Calculating b.p. elevation and f.p. depression
  • Because the type of solute doesn’t matter, you only need to know the amount of solute
  • Elevation & depression happen at a constant rate depending on the amount of solute added (number of moles)
    • Tb = Kbm (where Kb & Kf are the constants)
    • Tf = Kfm
try it
Try It
  • If you have .625 m aqueous solution with a nonvolatile, nonelectrolyte solute, what would the boiling point and freezing point be?
try it1
Try It
  • Calculate the freezing point and boiling point of a solution that contains 105.4 g NaCl dissolved in 750.3 ml H2O.
osmotic pressure
Osmotic Pressure
  • Osmosis is a natural process where the solvent flows across a membrane – always flows from where there is more solvent to where there is less solvent.
  • Adding solute to one side of the membrane will cause more solvent to flow that way.
  • This increases the osmotic pressure on that side of the membrane.
  • Ex: kidney dialysis

uptake of nutrients by cells