1. COLLIGATIVE PROPERTIES

2. Colligative Properties
- Properties that depend upon the number of solute particles in solution rather than the properties of the solute itself.
1)osmotic pressure
2)vapor pressure reduction
3)boiling point elevation
4)freezing point depression

3. Colligative Properties
1) In osmosis, solvent molecules move through a semi-permeable membrane from the less concentrated solution to the more concentrated solution. As a result the liquid levels become uneven. Eventually the pressure difference resulting from the different liquid levels become so large that the net flow of the solvent ceases.
The pressure required to prevent osmosis is
known as the osmotic pressure of the
solution.

4. Colligative Properties
2) If nonvolatile solute particles are added to a pure solvent, they will prevent some of the volatile solvent particles from leaving the liquid.
This results in a shift toward
more molecules in the liquid phase from
the gas phase, which causes a
reduction in vapor pressure.

5. Colligative Properties
3) Because the addition of nonvolatile solute reduces the vapor pressure of a liquid, a higher temperature is necessary to get the vapor pressure of the solution up to atmospheric pressure so that the solution boils.
The amount by which the boiling
temperature is raised is the
boiling point elevation.

6. Colligative Properties
The boiling point elevation is
directly proportional to the
molality and the number of particles
per formula unit of the solute.

7. Colligative Properties
Tb = Kb m n
Tb => boiling point elevation
Kb => molal boiling point elevation constant (0.52°C/m)
m => molality of solution (moles solute / kg solution)
n => number of particle per formula unit

8. Colligative Properties
Dissolution of ionic and
dissolving of covalent substance.
Look at example problems.
Why does salt melt ice?

9. Colligative Properties
4) The freezing point of a substance is the temperature at which the vapor pressures of the solid and the liquid phases are the same. If the solute is nonvolatile the vapor pressure of the solution is reduced. So the temperature at which the solution and the solid phase have the same vapor pressure is reduced.

10. Colligative Properties
This colligative property is known as
freezing point depression.
Like the boiling point elevation, the decrease in
the freezing point is directly proportional to the
molality and the number of particles per
formula unit of the solute.

11. Colligative Properties
 Tf = Kf m n
Tf => freezing point dpression
Kf => molal freezing point depression constant (1.86°C/m)
m => molality of solution (moles solute / kg solution)
n => number of particle per formula unit

12. COLLIGATIVE PROPERTIES
water & sugar-water evaporation animation
Boiling-Point Elevation and Freezing-Point Depression
Look at table of example substances.