1. Colligative properties

2. Colligative property- a property of a solution that depends on concentration of solute (the number of solute particles dissolved) but NOT on type of solute Colligative property- a property of a solution that depends on concentration of solute (the number of solute particles dissolved) but NOT on type of solute 3 colligative properties: 3 colligative properties: Vapor pressure reduction Vapor pressure reduction Boiling point elevation Boiling point elevation Freezing point depression Freezing point depression

3. Vapor pressure The pressure DIRECTLY above the surface of a liquid exerted by the molecules that have evaporated The pressure DIRECTLY above the surface of a liquid exerted by the molecules that have evaporated LOW vapor pressure = not much evaporation occurring LOW vapor pressure = not much evaporation occurring HIGH vapor pressure = lots of evaporation HIGH vapor pressure = lots of evaporation http://www.youtube.com/watch?v=re9r0kzQp_ M http://www.youtube.com/watch?v=re9r0kzQp_ M

4. Vapor pressure reduction Solute interferes with vaporization of water, therefore LOWERS the pressure of the vapor pressing down on surface Solute interferes with vaporization of water, therefore LOWERS the pressure of the vapor pressing down on surface

5. How does this influence boiling point & freezing point? Boiling Point: The temperature at which the vapor pressure of the liquid phase equals atmospheric pressure. Boiling Point: The temperature at which the vapor pressure of the liquid phase equals atmospheric pressure.

6. Boiling-Point Elevation Boiling point elevation: The difference in temperature between the boiling point of a SOLUTION and the boiling point of the pure solvent (). Boiling point elevation: The difference in temperature between the boiling point of a SOLUTION and the boiling point of the pure solvent (water). When a solute is dissolved in a solvent, the boiling point of the solvent will elevate (become higher) than the normal boiling point (will need more heat to boil) When a solute is dissolved in a solvent, the boiling point of the solvent will elevate (become higher) than the normal boiling point (will need more heat to boil)

7. Boiling point Elevation Because the bp is higher, the vapor pressure will be lowered Because the bp is higher, the vapor pressure will be lowered

8. Application: Adding salt to water while cooking pasta Water does not boil faster Water does not boil faster Water is boiling at a higher temperature so pasta cooks faster Water is boiling at a higher temperature so pasta cooks faster

9. More Examples – BP Elevation Antifreeze =a liquid added to the cooling system of a car to increases the BP of the water in it so it doesn’t overheat as fast in summer. Antifreeze =a liquid added to the cooling system of a car to increases the BP of the water in it so it doesn’t overheat as fast in summer.

10. Freezing-Point Depression Freezing-Point Depression: The difference in temperature between the freezing point of a solution and the freezing point of the pure solvent (). Freezing-Point Depression: The difference in temperature between the freezing point of a solution and the freezing point of the pure solvent (water). The presence of a solute in water disrupts the formation of the orderly pattern of ice. Therefore more kinetic energy must be transferred from the solution (into the surroundings) compared to the pure solvent to cause the solution to solidify. The presence of a solute in water disrupts the formation of the orderly pattern of ice. Therefore more kinetic energy must be transferred from the solution (into the surroundings) compared to the pure solvent to cause the solution to solidify.

11. Freezing Point Depression

12. Freezing point depression

13. Example – FP Depression Salt (solute) is added to melt ice (water = solvent) Salt (solute) is added to melt ice (water = solvent) Works by lowering the freezing point of water. Ex: 32° F normal freezing point of water, now it could be 15° F and still be in a liquid state. Works by lowering the freezing point of water. Ex: 32° F normal freezing point of water, now it could be 15° F and still be in a liquid state. Solid to liquid

14. Freezing-Point Depression The magnitude of the freezing-point depression is proportional to the number of solute particles dissolved in the solvent and does not depend upon their identity. The magnitude of the freezing-point depression is proportional to the number of solute particles dissolved in the solvent and does not depend upon their identity. Which would be a better salt for putting on icy roads, NaCl or CaCl 2 ? Which would be a better salt for putting on icy roads, NaCl or CaCl 2 ?

15. More Examples – FP Depression Antifreeze =a liquid added to the cooling system of a car to lower the FP of the water in it so it doesn’t freeze solid. Antifreeze =a liquid added to the cooling system of a car to lower the FP of the water in it so it doesn’t freeze solid. Some animals are able to survive freezing temperatures by producing natural antifreezes. Some animals are able to survive freezing temperatures by producing natural antifreezes. ▫ Natural antifreezes are just higher levels of alcohols (ex. glycerol) and sugars (ex. glucose) in the cells. Examples are box turtles, painted turtles and garter snakes, sugar maples and white spruce. Examples are box turtles, painted turtles and garter snakes, sugar maples and white spruce. http://videos.howstuffworks.com/discovery/52100-frozen-planet-caterpillar-survives-frozen-death-video.htm http://videos.howstuffworks.com/discovery/52100-frozen-planet-caterpillar-survives-frozen-death-video.htm http://videos.howstuffworks.com/discovery/52100-frozen-planet-caterpillar-survives-frozen-death-video.htm

16. Therefore… Because freezing point of water goes down, we can make things like Because freezing point of water goes down, we can make things like ICE CREAM!!!! ICE CREAM!!!!