Colligative Properties Honors Chemistry Chapter 14

14.4 Colligative Properties Colligative = “depends on the collection” Properties that depend on how many solute particles (concentration) are present ▫Does NOT depend on identity of solute It doesn’t matter what this is, only how many particles are present

Vapor Pressure Lowering Vapor pressure = pressure created by particles going from liquid to gas inside a closed container depend on the escaping tendency of solvent molecules from the liquid phase If you add solute, not as much solvent can escape into the gas phase Solute particles (red) block the solvent molecules (blue) from escaping More solvent escapes when there are fewer solute particles

Vapor Pressure Questions: 1.Which compound will lower the vapor pressure more in a liquid? a)0.1M N 2 O 5 b)0.7M N2 O 5 2. Which compound will lower the vapor pressure more in a liquid? a)1M NaCl b)0.5M NaCl WHY??

Boiling Point Elevation Boiling = liquid to gas The more solute added to a solution, the lower the vapor pressure and therefore the higher the boiling point Must add more energy to get it to boil --- b.p. will be hotter before solution will boil

Boiling Point Question: A solvent has a boiling point of 200°C. When 10 grams of salt is dissolved in the solvent, what is the most likely new boiling point? a. 210°C b. 200°C c. 190°C

Freezing Point Depression Freezing = solvent particles moving into solid crystalline form Solute gets in the way of making crystals preventing the solvent from freezing. Lower temperature is needed to freeze. Solute particles get in the way of allowing the crystalline structure to form Temperature must be lower for freezing to occur

Freezing Point Question A solvent has a freezing point of 10°C. What is the most likely freezing point if 5 grams of salt is mixed with the solvent? a. 5°C b. 10°C c. 15°C

Osmotic Pressure Increase Osmosis-movement of water from low to high concentration. Goal is to balance the concentrations. Osmotic Pressure Increases Water flows toward the side with more solute particles As water flows toward the side with more solute, the pressure increases

A brief overview… All matter has physical and chemical properties that determine its behavior One physical property is that all matter has a particulate nature (is made up of smaller particles such as atoms, molecules, and ions) The arrangement of these particles determines such properties as state, density, polarity, and crystalline structure

The arrangement is not the only thing that affects the behavior of matter… the number of particles can also play a role Colligative Properties are physical properties of solution that depend solely on the number of particles of solute and solvent present in solution. Examples: vapor pressure, boiling point, freezing point, and osmotic pressure

How do colligative properties affect everyday life? Ethylene glycol is the chemical name of a product found in most garages --- antifreeze Most people are aware of the importance of antifreeze when added to the water in the radiator of their cars… ▫It prevents the water in the radiator from boiling over ▫It prevents that same water from freezing in the winter

What the graph means… The graph was a representation of data collected when various concentrations of antifreeze were frozen with dry ice and then allowed to melt. The concentrations that took longer to melt had a higher melting point… thus a higher freezing point

What the graph represented… This graph was of the data obtained when those same antifreeze solutions were brought to a boil. The data graphed is of the boiling points in degrees Celsius of the various concentrations of antifreeze solutions.

So what does this mean in terms of taking care of our cars? When looking at the back of any antifreeze container, the manufacturer recommends using 50% antifreeze solution in your car. Why is this recommended over a 100% antifreeze solution? Does the experimental data support the manufacturer’s recommendations? Discuss why or why not with your class.