Colligative Properties of Solutions

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Colligative Properties of Solutions

• Boiling Pt Elevation and Freezing Pt Depression

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Colligative Properties

• depend only on the number of solute particles in
  a solution
• does not depend on the identity of particles

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Boiling Point Elevation

• a nonvolatile solute lowers the vapor pressure
• a higher T is required to reach the 1 atm of
  pressure which defines boiling point
• a nonvolatile solute elevates the boiling point
  of the solvent
• the amount of the elevation depends on
  concentration of the solute

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Freezing Point Depression

• vapor pressure of solid and liquid are equal at
  freezing point
• nonvolatile solute lowers the vapor pressure so a
  lower T is needed to decrease the vapor pressure
  to that of the solid
• a nonvolatile solute depresses the freezing point
  of the solvent
• the amount of the depression depends on
  concentration of the solute

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Example 1

• 18.00 g of glucose are added to 150.0 g of water.
  The boiling point of the solution is 100.34 C.
  The boiling point constant is 0.51 Ckg/mol.
• Find the molar mass of glucose.

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Example 1
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Example 1
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Example 2

• What mass of C2H6O2 (M62.1 g/mol) needs to be
  added to 10.0 L H2O to make a solution that
  freezes at -23.3C?
• density is 1.00 g/mL
• boiling point constant is 1.86Ckg/mol

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Colligative Properties of Solutions

• Osmotic Pressure

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Semi-permeable Membrane

• a partition that allows solvent particles to pass
  through but not solute particles
• separates a solution and a pure solvent

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Osmosis

• the flow of solvent through a semi-permeable
  membrane
• when the system has reached equilibrium, the
  water levels are different
• since there is greater hydrostatic pressure in a
  solution

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Osmotic Pressure

• the extra pressure in solution
• ?
• ? MRT
• where
• M is the molarity of the solution
• R is the gas law constant
• T is the temperature in Kelvin

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Example 3

• When 1.00x10-3 g of a protein is mixed with water
  to make 1.00 mL of solution, the osmotic pressure
  is 1.12 torr at 25.0C.
• Find the molar mass of this protein.

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Example 3
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Reverse Osmosis