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Outline for Today Wednesday, Dec. 5
• Chapter 11: Intermolecular Forces and Liquids
• Phase Changes
• Chapter 13: Properties of Solutions
• Solubility of Gases
• Colligiative Properties
!1
Example Problem
• Why is methanol (CH3OH) miscible in water but hexanol (CH3CH2CH2CH2CH2CH2OH) is not?
H3C
H2C
CH2
H2C
CH2
H2C
OHC OHH
HH
OH H
hexanolmethanol
water
Saturated Solutions
• Saturated solution: A solution that is at equilibrium with undissolved solute.
Additional solute will not dissolve.
solute + solvent solution
• The rate of dissolving is equal to the rate of crystalizing.
dissolve
crystalize
Supersaturated Solutions
Example Problem: Saturated solutions
Using the graph, will the addition of 40.0 g of potassium chloride to 100.0 g of water at 80oC lead to a saturated solution or unsaturated solution?
Solubility of gases• Henry’s Law Solubility of a gas increases directly with
increasing pressure
More collisions with the surface of the liquid increases dissolving.
Sg=kPg
Temperature Effects• Solubility of (most) solids increases with increasing temperature.
• Solubility of gases decreases with increasing temperature.
• Why?
• The best answer involves entropy!
• Higher the temperature, the higher the kinetic energy of all substances.
• The higher the kinetic energy, the more likely for the dissolved gas to escape the solution and become a gas.
Let’s try it!
Units of Concentration
• Molarity (M) =
• Molality (m) =
• Mole Fraction (X) =
Moles of Solute
Liters of Solution
Moles of Solute
Kilograms of Solvent
Moles of Solute
Total Moles
Units of Concentration
• Mass Percent =
• parts per million (ppm) =
• parts per billion (ppb) =
mass of solute
total mass of solution
mass of solute
total mass of solution
x 100
x 106
mass of solute
total mass of solutionx 109
Colligative Properties Depend on the Concentration (not identity) of Solute
Particles
• The lowering of Vapor Pressure depends on the mole fraction of the solvent.
• The increase of Osmotic Pressure increase depends on the molarity (M) of the ions.
• Freezing Point Depression depends on molality (m)
• Boiling Point Elevation depends on molality (m).
Vapor Pressure• Vapor Pressure Lowering depends on mole fraction.
• Raoult’s Law:
Osmotic Pressure• Osmotic Pressure: Net movement of solvent (water) from
low concentration areas to high concentration areas across a semipermeable membrane.
Osmotic Pressure• Osmotic Pressure increases as MOLARITY increases
Boiling Point ElevationPure Solvent
Solution
Boiling Point ElevationPure Solvent
Solution
∆Tb=Tb(solution)-Tb(pure solvent) =iKbm
Freezing Point DepressionPure SolventSolution
Freezing Point DepressionPure SolventSolution
∆Tf=Tf(solution)-Tf(pure solvent) =iKfm
Example Problem: Freezing Point Depression
• Below is a table of van’t Hoff Factors (Kb and Kf) but water is missing!
• What is Kb if the freezing point of 500.0 g of water with 25.0 g of calcium chloride dissolved in it is 2.5 oC?
∆Tf=Tf(solution)-Tf(pure solvent) =iKfm
Example Problem: Boiling Point Elevation
• How many grams of salt (NaCl) would you have to add to 2.0 kg of pasta water to raise the boiling point 5oC?
• 1 tablespoon of NaCl is 25 g. How many tablespoons is that?
∆Tb=Tb(solution)-Tb(pure solvent) =iKbm
Example Problem: Osmotic Pressure
• What molarity of sodium chloride would a solution have to be to have an osmotic pressure equal to the osmotic pressure of blood which is 7.7 atm at 25 oC?
Example Problem: Vapor Pressure
• Sort the following by increasing vapor pressure of water:
• A) A solution 10.0 g of glucose (C6H12O6)
• B) A solution of 10.0 g of sucrose (C12H22O11)
• C) A solution of 10.0 g of methanol (CH3OH)