Outline for Today Wednesday, Dec. 5 Chapter 11: Intermolecular - - PowerPoint PPT Presentation

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 H2 C C H2 H2 C C H2 H2 C OH

C OH H H H

O H H

hexanol methanol 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 solution x 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 Elevation

Pure Solvent Solution

Boiling Point Elevation

Pure Solvent Solution

∆Tb=Tb(solution)-Tb(pure solvent) =iKbm

Freezing Point Depression

Pure Solvent Solution

Freezing Point Depression

Pure Solvent Solution

∆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)