Colligative Properties

C11-1-12 MOLECULAR PROPERTIES OUTCOME QUESTION(S): C11-1-12 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

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

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

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

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

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

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…

C11-1-12 MOLECULAR PROPERTIES CAN YOU / HAVE YOU? C11-1-12 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