1. Colligative Properties

2. C11-1-12 MOLECULAR PROPERTIES
OUTCOME QUESTION(S):
C MOLECULAR PROPERTIES
Define normal boiling point temperature in terms of vapour pressure.
Include: volatility, dynamic equilibrium
Interpolate and extrapolate information from pressure versus temperature graphs and heating/cooling curves.
Explain colligative properties like freezing-point depression and boiling-point elevation at the molecular level.
Vocabulary & Concepts

3. We will focus on the effects of solute on the first three properties
Colligative Properties:
Physical properties of solutions that are affected by the concentration (not identity) of solute dissolved.
Vapour Pressure
Boiling Point
Freezing Point
Osmotic Pressure
We will focus on the effects of solute on the first three properties

4. Vapour pressure:
Predict how a solute might affect this…
Pressure of vapour at equilibrium is reduced with addition of a solute (independent of temperature).
solute takes up space at the surface and prevents solvent particles from vaporizing
Remember: particles experience less IMF at the surface
VAPOUR
LIQUID

5. Boiling Point:
Prediction?
Boiling point of a solvent is elevated with addition of a solute – higher temperature at boiling.
Remember: boiling point is when vapour equals air pressure - allowing internal vapour to form
solute takes up space and prevents solvent particles vaporizing enough to equalize air pressure

6. Freezing Point:
Prediction?
Freezing point of a solvent is depressed with addition of a solute – lower temperature at freezing.
solute takes up space and prevents IMF from pulling particles into crystalline structure
Difficult to organize – particles must lose more kinetic energy (slow down) to phase change Na Cl Cl Na
0oC
0oC

7. Line B must be the solution - it has lower vapour pressure
Which line on this vapour pressure graph would represent the effects of adding a solute?
Solutes lower the ability of a solvent to vaporize (at any temperature)
Line B must be the solution - it has lower vapour pressure

8. From the heating curve below:
Draw how this graph would change with the addition of a solute?
Solutes interfere with phase changes
The plateau and boiling point would happen at a higher temperature
And the melting point would lower too…

9. C11-1-12 MOLECULAR PROPERTIES
CAN YOU / HAVE YOU?
C MOLECULAR PROPERTIES
Define normal boiling point temperature in terms of vapour pressure.
Include: volatility, dynamic equilibrium
Interpolate and extrapolate information from pressure versus temperature graphs and heating/cooling curves.
Explain colligative properties like freezing-point depression and boiling-point elevation at the molecular level.
Vocabulary & Concepts