1. Colligative Properties

2. Explain freezing-point depression and boiling-point elevation at the molecular level.
Additional KEY Terms
Colligative Properties

3. Vapour Pressure / Boiling point / Freezing point
Colligative Properties:
Physical properties of solutions that are affected by the number (not identity) of solute particles dissolved.
Vapour Pressure / Boiling point / Freezing point

4. Remember: particles at the surface have fewer IMFs.
Vapour pressure: Pressure of vapour at equilibrium with its liquid in a closed container.
evaporation = condensation
Remember: particles at the surface have fewer IMFs.

5. Fewer particles evaporate = LESS V. PRESSURE
solutes take up space and prevent solvent particles from reaching surface.
Fewer particles evaporate = LESS V. PRESSURE

6. More energy needed to boil = HIGHER BP
Boiling point: temperature needed for vapour particles to have pressure equal to air pressure for escape.
solutes take up space and prevent solvent particles from getting close to the heat source.
More energy needed to boil = HIGHER BP

7. Freezing point: temperature needed for liquid particles to lose energy and phase change to solid.Na Na Cl
solutes take up space and prevent solvent particles from forming crystalline structure.
Difficult to form solids = LOWER FP
Particles must ‘slow down’ more to connect to each other.

8. CAN YOU / HAVE YOU?
Explain freezing-point depression and boiling-point elevation at the molecular level.
Additional KEY Terms
Colligative Properties