COLLIGATIVE PROPERTIES

COLLIGATIVE PROPERTIES

1. Physical properties of solutions that depend on the number of solute particles and not on the nature of the solute particles.

2. Depend on the particles in the solution...

   • Soluble vs Non-soluble substance
   • Electrolyte vs Non electrolyte

3. Properties

   • Vapor pressure lowering
     • Vapor pressure
       • The pressure exerted by the particles of vapor above a liquid
     • If a solute is non volatile, the vapor pressure of its solution is always less than that of the pure solvent.
     • Less volatile molecules in the surface of the solution make the vapor pressure to decrease.
   • Boiling point elevation
     • Because the presence of a non volatile solute lowers the vapor pressure of a solution, more temperature is needed to evaporate it. Then, the boiling point increases….
   • Freezing point depression
     • When a solute is added to water, the freezing point of the solution decreases.
     • A solution must be cooled to a lower temperature than the pure solvent in order for freezing to occur
   • Osmotic pressure
     • Net movement of solvent molecules (water) through a semipermeable membrane from a diluted solution to a more concentrated solution.
     • The osmotic pressure of a solution is the pressure required to stop osmosis.
     • The greater the number of particles disolved in a solution, the higher its osmotic pressure.
     • Water purification: Reverse osmosis
       • Pressure is applied to overcome the osmotic pressure of the polluted water.