; Chapter 14 Ions in Aqueous Solutions and Colligative Properties
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Chapter 14 Ions in Aqueous Solutions and Colligative Properties

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									         Chapter 14:
Ions in Aqueous Solutions and
    Colligative Properties

 Section 2:
 Colligative Properties of Solutions
   Overview

• We will examine what colligative properties
  are.
• We will define the main colligative properties.
   What Are They?

• Colligative Properties – Properties that
  depend on the concentration of solute
  particles, but not on their identity.
• Non-volatile Substance – One that has little
  tendency to become a gas under existing
  conditions.
  Vapor-Pressure Lowering

• By adding certain
  solutes the vapor
  pressure of some
  solvents can be
  lowered.
Freezing Point Depression

• The solution also lowers the freezing point of the
  solvent alone.
• Molal Freezing Point Constant – (Kf) It is for one
  molal (m) of a nonvolitile, nonelectrolyte solute.
• To calculate the freezing point depression we use
  the following equation:
• Δtf = Kf m
• Kf = oC/m
• m = molality
   Boiling Point Elevation

• By adding solute it causes the boiling point of
  the solvent to rise.
• Molal Boiling Point Constant – (Kb) It is for one
  molal (m) of a nonvolitile, nonelectrolyte
  solute.
• Δtb = Kb m
• Kb = oC/m
• m = molality
   Osmotic Pressure

• Semipermeable Membrane – A membrane
  that allows the movement of some particles
  while blocking the movement of others.
• Osmosis – The movement of solvent through
  a semipermeable membrane from the side of
  lower solute concentration to the side of higher
  solute concentration.
• Osmotic Pressure – The external pressure
  that must be applied to stop osmosis.
 Electrolytes
• Electrolytes tend to depress the
  freezing point greatly.
• They also tend to elevate the boiling
  point greatly as well.
• That is why we use salt to get rid of ice
  or to prevent the formation of ice.

								
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