CHEM

• Colligative properties


  Properties that depend solely on the number of particles of solute present but not on the kind and nature of solute
• Colligative properties depend on the amount of the solute and not on their chemical identities
• Nonelectrolyte solute


  Does not ionize in solution, so the number of solute particles will be less than in a solution containing an electrolyte solute
• The effect of an electrolyte solute will be greater than a nonelectrolyte solute in a solution
• Colligative property


  A property that depends only upon the number of solute particles (concentration), and NOT upon their identity
• Four important colligative properties of solutions

  • Vapor-pressure lowering
  • Boiling-point elevation
  • Freezing-point depression
  • Osmotic pressure
• Vapor pressure


  The pressure exerted by a vapor that is in dynamic equilibrium with its liquid
• A solution that contains a solute that is not easily vaporized always has a lower vapor pressure than the pure solvent
• Volatile substance


  A substance that evaporates readily, has a high escaping tendency and high vapor pressure
• Non-volatile substance


  Has a low vapor pressure because it has a low escaping tendency
• A non-volatile solute is dissolved in water


  The solute molecules take up space at the surface and thus preventing the escape of the solvent molecules
• In a solution, the interaction between the solute and the solvent is greater than the solvent-solvent interaction


  This makes it more difficult for the molecules to escape, lowering the vapor pressure of the solution
• The greater the concentration of solute present

  The greater the vapor pressure reduction
• A solution containing an electrolyte solute

  Will have a lower vapor pressure than a solution containing a nonelectrolyte solute
• Freezing-point depression


  The difference in temperature between the freezing point of a solution and the freezing point of the pure solvent (water)
• The presence of a solute in water disrupts the formation of the orderly pattern of ice, requiring more kinetic energy to be withdrawn to cause the solution to solidify
• The magnitude of the freezing-point depression

  Is proportional to the number of solute particles dissolved in the solvent and does not depend upon their identity
• Electrolytes as solutes have a greater effect on freezing-point depression than nonelectrolytes because electrolytes ionize in solution and contain a greater number of particles</b>
• Boiling point


  The temperature at which the vapor pressure of the liquid phase equals atmospheric pressure
• Boiling-point elevation


  The difference in temperature between the boiling point of a solution and the boiling point of the pure solvent
• The boiling point of a solution is higher than the boiling point of the pure solvent
• The magnitude of the boiling-point elevation

  Is proportional to the number of solute particles dissolved in the solvent
• Osmosis


  The movement of solvent through a semipermeable membrane from a region of low concentration to a region of high concentration
• If the semipermeable membrane is placed in between two solutions of different concentrations, the solvent will flow from the less concentrated solution to the more concentrated solution until the concentration on both sides are the same
• Osmotic pressure


  The pressure needed to prevent osmosis, applied to the more concentrated solution so the solvent flows from the more concentrated to the less concentrated solution (reverse osmosis)