15-4 Colligative Properties

Colligative property: A property that depends on the concentration of solute particles, but is independent of their nature A property that depends on the concentration of solute particles, but is independent of their nature The four colligative properties are: The four colligative properties are: 1. Vapor pressure reduction 2. Boiling point elevation 3. Freezing point depression 4. Osmotic pressure

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 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. Related directly to the conc. of a soln. Double conc., double vpr effect Double conc., double vpr effect Raoult’s Law: magnitude of vapor reduction is proportional to solution concentration Raoult’s Law: magnitude of vapor reduction is proportional to solution concentration

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

BPE – real life examples 1. Making candy: use a lot of sugar and a little flavoring, as water is boiled away, the conc. of sugar goes up. 2. Making maple syrup 3. Need for antifreeze even in the summer

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

FPR – real life examples 1. Salt on winter roads 2. Antifreeze in your car 3. Making homemade ice cream

Osmotic Pressure Semi-permeable: a membrane that allows some particles to pass, but not others 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 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 Osmotic pressure: the pressure required to prevent osmosis

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

Osmotic Pressure Real life examples: Real life examples: 1. Feeling bloated when you eat salty foods – salt solutions in your body are more concentrated that usual 2. Pickles: cucumbers that have been soaked in a salt solution – they lose water through osmosis 3. Country ham: the salt on the ham causes bacteria on it to shrivel and die 4. Plants: movement of water from soil to plant roots