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15-4 Colligative Properties

15-4 Colligative Properties. Colligative property:. A property that depends on the concentration of solute particles, but is independent of their nature The four colligative properties are: Vapor pressure reduction Boiling point elevation Freezing point depression Osmotic pressure.

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15-4 Colligative Properties

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  1. 15-4 Colligative Properties

  2. Colligative property: • A property that depends on the concentration of solute particles, but is independent of their nature • The four colligative properties are: • Vapor pressure reduction • Boiling point elevation • Freezing point depression • Osmotic pressure

  3. Vapor Pressure Reduction (VPR) • Occurs when the pressure of the vapor over a solvent is reduced when a nonvolatile solute is dissovled in the solvent • Related directly to the conc. of a soln. • Double conc., double vpr effect • Raoult’s Law: magnitude of vapor reduction is proportional to solution concentration

  4. Boiling Point Elevation (BPE) • The amount to which the dissolved solute raises the boiling point of its soln. • Related directly to the conc. of a soln. • Double conc., double boiling point elevation

  5. BPE – real life examples • Making candy: use a lot of sugar and a little flavoring, as water is boiled away, the conc. of sugar goes up. • Making maple syrup • Need for antifreeze even in the summer

  6. Freezing Point Reduction (FPR) • The amount to which the dissolved solute lowers the freezing point of its soln. • Related directly to the conc. of a soln. • Double conc., double freezing point depression

  7. FPR – real life examples • Salt on winter roads • Antifreeze in your car • Making homemade ice cream

  8. Osmotic Pressure • Semi-permeable: a membrane that allows some particles to pass, but not others • Osmosis: the net flow of solvent molecules from the less concentrated solution to the more concentrated solution • Osmotic pressure: the pressure required to prevent osmosis

  9. Osmotic Pressure • Isotonic: identical osmotic pressure results in no osmosis • Hypotonic: lower osmotic pressure than another (cells burst) • Hypertonic: higher osmotic pressure than another (cells shrivel)

  10. Osmotic Pressure • Real life examples: • Feeling bloated when you eat salty foods – salt solutions in your body are more concentrated that usual • Pickles: cucumbers that have been soaked in a salt solution – they lose water through osmosis • Country ham: the salt on the ham causes bacteria on it to shrivel and die • Plants: movement of water from soil to plant roots

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