Colligative Properties

• Non-Colligative Properties

  • Properties that depend on the identity of the dissolved solute and the solvent.
• Colligative Properties

  • Properties that depend on the number of solute particles in a solution (concentration) but not its identity
• Vapor Pressure Lowering

  • is the pressure exerted by a vapor that is in dynamic equilibrium with its liquid in a closed system.
• The relationship between the vapor pressure of the solution and the vapor pressure of the solvent depends on the concentration of the solute in the solution.
• the higher the concentrration of solution, the lower the vapor pressure
• Equilibrium is established between the liquid and vapor in a pure solvent.
• Nonvolatile solutes reduces the ability of solvent molecules to escape, thus lowering the vapor pressure.
• A solution that contains a solute that is nonvolatile always has a lower vapor pressure than the pure solvent.
• Ionic solutes that dissociate have greater effects on vapor pressure than does a non-dissociating solute.
• Boiling Point Elevation

  • is the temperature at which the vapor pressure of the liquid phase equals the atmospheric pressure
• Therefore, a higher temperature is required to boil the solution than the pure solvent.
• The difference in temperature between the boiling point of a solution and the boiling point of the pure solvent is the boiling-point elevation.
• Addition of solute will decrease the vapor pressure and so will decrease the freezing point.
• Osmotic Pressure

  • The minimum pressure that needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane.
• In osmosis, there is net movement of solvent from the area of lower solute concentration to the area of higher solute concentration.
• van’t Hoff factor

  • Depends on the number of electrolytes that can be produced on a single compound