Colligative PropertiesHonors ChemistryChapter 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 soluteIt 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 N2O5

b) 0.7M N2O5

2. Which compound will lower the vapor pressure more in a liquid?

c) 1M NaCld) 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°Cb. 200°Cc. 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°Cb. 10°Cc. 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.