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1. Chapter 13 Section 5: Colligative Properties Colligative properties depend on quantity of solute molecules.
Boiling Point Elevation
When a solute is dissolved in a solvent, the solute reduces the ability of the surface solvent molecules to escape the liquid.
The vapor pressure of the solvent is lowered, therefore the temperature at which the solution will boil will be higher than before.
Example: Sugar water will boil at a temperature above 100 šC.
Why?
The sugar lowers the vapor pressure of water. So the water molecules near the surface of the liquid have a more difficult time escaping into the vapor phase and the temperature has to be higher in order for them to break away.
2. Vapor Pressure of Solutions