Why do you put antifreeze in your car radiator?
Can you cook spaghetti faster in salt water?
Why is salt placed on roads to keep ice from
forming?
All of these questions can be answered by
colligative properties.
Properties that depend on the concentration
(numbers) of solute particles but not on their
identity are called colligative properties.
•The presence of solutes affects the properties
of solutions.
•Some of these properties are not dependent on
the nature of the dissolved substance but only
on how many dissolved particles are present.
•Explains the value of putting
antifreeze in your radiator to keep a
car from overheating.
Remember vapor pressure is the pressure caused by
molecules in the gas phase that are in equilibrium
with the liquid phase.
The vapor pressure of a solvent containing a
nonvolatile solute (doesn’t want to form a gas) is lower
than the vapor pressure of the pure solvent (same
temp.).
Increase number of solute particles
Decreased opportunities for solvent particles to escape solution
Result: Fewer solvent particles to evaporate and lower
vapor pressure.
More solute particles = Decreasing vapor pressure
Remember colligative properties based
on numbers of solute particles!!!!
Explains why salt is placed on roads to keep ice
from forming.
Freezing-point depression is a colligative property
of a liquid solution by which the freezing point of
the solution is lower than that of the pure solvent.
Remember with a solution, the vapor pressure is lower. This
means the solution remains liquid over a larger temperature
range.
In other words, impurities in a substance cause a change in
its phase diagram by making the liquid region bigger.
Explains how you can cook spaghetti faster in
salt water.
Boiling point elevation is a colligative property of
a solution by which the solution’s boiling point is
higher than that of the pure solvent.
Impact of solute on a colligative property.
1 mol of sugar = 1 mol Na+ = 1 mol O2- = 1 mol urea
= 1 mol pickles
All do the exact same thing!!!
Same number of solute particles!!!
Create a Colligative Properties
Foldable
Be sure to include:
• Definition of
colligative properties
• 3 Examples of
colligative properties
with explanation
• Creativity & Neatness
Use your notes & pages
446 – 451 to help
you.