Colligative propertiesColligative properties

Colligative propertiesColligative properties

Colligative property- a property of a Colligative property- a property of a solution that depends on concentration of solution that depends on concentration of solute (the number of solute particles solute (the number of solute particles dissolved) but NOT on type of solutedissolved) but NOT on type of solute

3 colligative properties:3 colligative properties:Vapor pressure reductionVapor pressure reductionBoiling point elevationBoiling point elevationFreezing point depressionFreezing point depression

Vapor pressureVapor pressure

The pressure DIRECTLY above the The pressure DIRECTLY above the surface of a liquid exerted by the surface of a liquid exerted by the molecules that have evaporatedmolecules that have evaporated

LOW vapor pressure = not much LOW vapor pressure = not much evaporation occurringevaporation occurring

HIGH vapor pressure = lots of evaporationHIGH vapor pressure = lots of evaporation http://www.youtube.com/watch?v=re9r0kzQp_M

Vapor pressure reductionVapor pressure reduction

Solute interferes with vaporization of Solute interferes with vaporization of water, therefore LOWERS the pressure of water, therefore LOWERS the pressure of the vapor pressing down on surfacethe vapor pressing down on surface

How does this influence boiling How does this influence boiling point & freezing point?point & freezing point?

Boiling Point: The temperature at which Boiling Point: The temperature at which the vapor pressure of the liquid phase the vapor pressure of the liquid phase equals atmospheric pressure.equals atmospheric pressure.

Boiling-Point ElevationBoiling-Point Elevation

Boiling point elevation: The Boiling point elevation: The difference in temperature between difference in temperature between the boiling point of a SOLUTION the boiling point of a SOLUTION and the boiling point of the pure and the boiling point of the pure solvent (solvent (water).).

When a solute is dissolved in a When a solute is dissolved in a solvent, the boiling point of the solvent, the boiling point of the solvent will elevate (become solvent will elevate (become higher) than the normal boiling higher) than the normal boiling point (will need more heat to boil)point (will need more heat to boil)

Boiling point ElevationBoiling point Elevation

Because the bp is higher, the vapor Because the bp is higher, the vapor pressure will be loweredpressure will be lowered

Application: Adding salt to water Application: Adding salt to water while cooking pastawhile cooking pasta

Water does not Water does not boil fasterboil faster

Water is boiling Water is boiling at a higher at a higher temperature so temperature so pasta cooks pasta cooks fasterfaster

More Examples – BP ElevationMore Examples – BP ElevationAntifreeze =a liquid added to the cooling Antifreeze =a liquid added to the cooling

system of a car to increases the BP of the system of a car to increases the BP of the water in it so it doesn’t overheat as fast in water in it so it doesn’t overheat as fast in summer. summer.

Freezing-Point DepressionFreezing-Point Depression

Freezing-Point Depression: The difference Freezing-Point Depression: The difference in temperature between the freezing point in temperature between the freezing point of a solution and the freezing point of the of a solution and the freezing point of the pure solvent (pure solvent (water).).The presence of a solute in water disrupts the The presence of a solute in water disrupts the

formation of the orderly pattern of ice. formation of the orderly pattern of ice. Therefore more kinetic energy must be Therefore more kinetic energy must be transferred from the solution (into the transferred from the solution (into the surroundings) compared to the pure solvent to surroundings) compared to the pure solvent to cause the solution to solidify.cause the solution to solidify.

Freezing Point DepressionFreezing Point Depression

Freezing point depressionFreezing point depression

Example – FP DepressionExample – FP DepressionSalt (solute) is added to melt ice (water = Salt (solute) is added to melt ice (water =

solvent) solvent) Works by lowering the freezing point of water. Works by lowering the freezing point of water.

Ex: 32° F normal freezing point of water, now it Ex: 32° F normal freezing point of water, now it could be 15° F and still be in a liquid state.could be 15° F and still be in a liquid state.

Solid to liquid

Freezing-Point DepressionFreezing-Point Depression

The magnitude of the The magnitude of the freezing-point depression freezing-point depression is proportional to the is proportional to the number of solute particles number of solute particles dissolved in the solvent dissolved in the solvent and does not depend upon and does not depend upon their identity.their identity.Which would be a better salt Which would be a better salt

for putting on icy roads, for putting on icy roads, NaCl or CaClNaCl or CaCl22??

More Examples – FP DepressionMore Examples – FP Depression• Antifreeze =a liquid added to the cooling system of Antifreeze =a liquid added to the cooling system of

a car to lower the FP of the water in it so it doesn’t a car to lower the FP of the water in it so it doesn’t freeze solid. freeze solid.

• Some animals are able to survive freezing Some animals are able to survive freezing temperatures by producing natural antifreezes.temperatures by producing natural antifreezes.▫ Natural antifreezes are just higher levels of alcohols (ex. Natural antifreezes are just higher levels of alcohols (ex.

glycerol) and sugars (ex. glucose) in the cells.glycerol) and sugars (ex. glucose) in the cells.• Examples are box turtles, painted turtles and Examples are box turtles, painted turtles and

garter snakes, sugar maples and white spruce.garter snakes, sugar maples and white spruce.• http://videos.howstuffworks.com/discovery/52100-frozen-planet-caterpillar-survives-frozen-death-video.htm

Therefore…Therefore…

Because freezing point of water goes Because freezing point of water goes down, we can make things likedown, we can make things like

ICE CREAM!!!!ICE CREAM!!!!