Colligative Properties

• Electrolyte


  Substance that forms when dissolved in water, which is then able to conduct a current (conductivity)
• In an aqueous solution, a strong electrolyte is considered to be completely ionized or dissociated in water, meaning it is soluble
• Ionic compound that are not completely dissociated or ionized in water are classified as weak electrolyte
• Major Positive Ions (Cations)

  A) Major Positive Ions (Cation)

  B) Sodium

  C) Potassium

  D) Calcium

  E) Magnesium

  
• Major Negative Ions (Anions)

  A) Chloride

  B) Bicarbonate

  C) Phosphate

  D) Sulfate

  
• Nonelectrolytes

  Compound that does not ionize in solution at all

  ✓ Will not conduct electricity

  ✓ Such as sugar and ethanol: which are primarily held

  together by covalent rather than ionic compounds

  are Nonelectrolytes
• Strong electrolytes have greater effect on the

  properties of solution
• Colligative Properties

  Depend only on the number of solute particles present

  (concentration), not on the identity of the solute

  particles.
• COLLIGATIVE PROPERTIES

  Vapor pressure lowering

  Boiling point elevation

  Freezing point depression

  Osmotic pressure
• Vapor Pressure Lowering


  The vapor pressure of a liquid is determined by how easily its molecules overcome the attractive forces and are able to escape the surface of the liquid then enter the gaseous phase
• Vapor Pressure Lowering

  • Nonvolatile solutes reduce the ability of surface solvent molecules to escape the liquid. Therefore, vapor pressure is lowered

  The amount of vapor pressure lowering depends upon the number of solute particles
• Boiling Point Elevation


  The boiling point is the temperature at which the vapor pressure of a liquid is equal to the atmospheric pressure
• Boiling point elevation is a colligative property related to vapor pressure lowering

  Due to the lowering of the vapor pressure of the solvent when a solution forms, a solution will require a higher temperature than the pure solvent to reach its boiling point.
• Freezing Point Depression

  • The freezing point of a liquid is the temperature at which a liquid becomes a solid.

  Presence of a solute interferes with solid formation, requires more kinetic energy be withdrawn for solution to freeze
• Phase diagram illustrating the boiling point elevation and freezing point depression of aqueous solution

  A) Liquid

  B) Vapor

  C) Solid

  
• Osmotic Pressure


  the osmotic pressure of a solution is the difference in pressure between the solution and the pure liquid solvent when the two are in equilibrium across a semipermeable membrane
• Osmosis is the diffusion of a solvent through a semipermeable membrane
• ISOTONIC

  If two solutions are of equal concentration and, hence, have the same osmotic pressure

  
• HYPOTONIC


  If two solutions are of unequal osmotic pressures and the more dilute solution (low osmotic pressure)

  
• HYPERTONIC


  If two solutions are of unequal osmotic pressures and the more concentrated solution (high osmotic pressure)

  
• BOILING POINT ELEVATION

  
• MELTING POINT ELEVATION

  
• OSMOTIC PRESSURE

  
• What is “i ”?

  
• Van’t hoff factor (i)


  The reason is that electrolytes dissociate into ions in solution, and so one unit of an electrolyte compound separates into two or more particles when it dissolves Thus i for nonelectrolytes is 1 and for electrolytes is greater than 1
• BOILING POINT ELEVATION

  
• MELTING POINT DEPRESSION

  
• BOILING POINT ELEVATION AND MELTING POINT DEPRESSION OF DIFFERENT SOLVENT