Chapter 13: Solutions and Their Properties

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Chapter 13 Solutions and Their Properties
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Chapter 13 Outline

• The Solution Process
• Energy changes
• Saturated Solutions and Solubility
• Factors Affecting Solubility
• Ways of Expressing Concentration
• Colligative Properties
• Vapor Pressure Lowering, BP Elevation, FP
  Depression, Osmosis
• Fractional Distillation of Liquid Mixtures

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Solutions

• Solution
• mixture of two or more substances
• components are the solute and the solvent
• Solvent
• component of the mixture present in greater
  quantity
• often retains its physical characteristics
• Solute
• component of the mixture present in smaller
  quantity

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Solution Process

• Intermolecular Forces
• must be overcome in both the solvent solute
  before the mixture can be formed
• forces between the solute solvent must be
  similar in nature and strength
• hydration
• interaction between water (the solvent) solute
  is termed hydration
• solvation
• interaction between any solvent the solute

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Ion-Dipole
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Hydration of NaCl
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05_09.jpg
A
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Energy Changes And Solution Formation
NaCl dissolves in water because water has
sufficient attraction for the Na and Cl- ions to
overcome the attraction for one another in the
crystal
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Energy Relationships

• DHsolution DH1 DH2 DH3
• DH1 energy required to separate solute
  particles
• DH2 energy required to separate solvent
  particles
• DH3 energy produced by interaction of
  solute/solvent
• DHsolution is exothermic only if
• DH3 is larger than DH1 DH2

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Solubility

• General Rule -- like dissolves like
• polar substances will dissolve other polar
  substances
• non-polar substances will dissolve other
  non-polar substances
• polar substances will not dissolve non-polar
  substances

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Solubility
Processes in which the order of the system
increases tend to occur spontaneously
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Solubility

• Polar/Polar solutions
• driven by energy relationships -- DH3 is larger
  than DH1 DH2
• Non-polar/Non-polar solutions
• driven by disorder -- DH3 is about the same as
  DH1 DH2

I2 in hexane
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Cell Membrane
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Conceptual Question

• The dissolution of water in octane (C8H18) is
  prevented by__________?
• London dispersion forces between octane molecules
• Hydrogen bonding between water molecules
• Dipole-dipole attraction between octane molecules
• Ion-dipole attraction between water and octane
  molecules
• Repulsion between like-charged water and octane
  molecules

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Conceptual Question

• When two nonpolar organic liquids are mixed, a
  solution forms and the enthalpy of solution is
  quite small. Label the two organic liquids as A
  (solvent) and B (solute). The formation of
  solution is favored by__________
• Hydration of the solute, B
• The equal enthalpy of the solvent and solute
• The highly negative enthalpy of the solution
  process
• Solvation of the solvent, A
• An increase in disorder, since A-A, B-B, and A-B
  interactions are similar

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Saturated Solutions Solubility

• Process
• solute solvent solution
• Solubility
• quantity of solute necessary to produce a
  saturated solution
• generally in grams of solute per 100 grams or mL
  of water

Solution formation
crystallization
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Saturated Solutions Solubility

• Saturated Solution
• solution is in equilibrium with undissolved
  solute
• solution contains the maximum amount of solute
  possible
• Unsaturated Solution
• solution contains less than the maximum amount of
  solute
• there is no undissolved solute present
• Supersaturated Solution
• solution contains more than the maximum amount of
  solute
• there is no undissolved solute present
• solution is unstable

A
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05_25.jpg
35.7 g/100 ml At 0 C
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Factors Affecting Solubility

• Solute-Solvent Interactions
• types of solute/solvent -- polar or non-polar
• like dissolves like
• pairs of liquids which are soluble in all
  proportions are miscible
• pairs which are not soluble are immiscible
• The stronger the attractions between solute and
  solvent the, greater the solubility

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Conceptual Question

• Which of the following is the most soluble in
  water?
• a. CH3CH2OH
• b. CH3CH2CH2OH
• c. CH3CH2CH2CH2OH
• d. CH3OH

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Factors Affecting Solubility
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Solubilities of some Alcohols in Water
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Factors Affecting Solubility
The number of -OH groups within a molecule
increases solubility in water.
Glucose
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Factors Affecting Solubility

• Pressure
• solubility of gases increase with
• increasing pressure
• increasing mass

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Factors Affecting Solubility

• Henrys Law relationship between pressure and
  solubility of a gas Å
• Sg kPg
• Sg is solubility of the gas
• Pg is partial pressure of gas
• k is a constant
• Carbonated beverages are bottled under gt 1
  atm. As the bottle is opened,
  decreases and the solubility of CO2 decreases.
  Therefore, bubbles of CO2 escape from solution.

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Calculation

• Calculate the concentration of CO2 in a soft
  drink after the bottle is opened and equilibrates
  at 25 C under a CO2 partial pressure of 3.0 x
  10-4 atm. (Henrys Law constant 3.1 x 10-2
  mol/L-atm)

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Factors Affecting Solubility

• Temperature
• generally, solubility of solids increases with
  increasing temperature

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Factors Affecting Solubility

• solubility of gases
• decreases with
• increasing
• temperature

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Conceptual Question

• The lowest value of the Henrys Law constant for
  methane (CH4) will be obtained with _________ as
  the solvent and a temperature of ___________ K?
• a. C5H12, 301
• b. C6H6, 322
• c. H20, 301
• d. H2O, 301

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Concentration

• Dilute - not a lot of solute
• Concentrated - a large amount of solute.
• strong solution - as in a strong cup of tea
• Concentration can be expressed quantitatively is
  many ways
• Molarity, Molality, percentage, mole fraction,
  etc

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Molarity

• The molarity is the number of moles of solute in
  1 litre of solution
• M moles of solute
• liters of solution
• 1M solution is fairly concentrated
• Millimolar 0.001M 1?10-3moles/L
• 1 millimole/L
• 1mM

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Mole fraction

• If a solution consists of mA moles of A, mB moles
  of B, mC moles of C, etc.
• Mole fraction of A
• XA mA / (mA mB mC)
• XA XB XC 1

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Mass percentage

• A solution that is 36 HCl by mass, contains 36 g
  HCl in 100 g of solution.
• Milk is not a true solution, but 2 milk refers
  to 2 g of milk fat in 100 g of milk.
• You may see figures on packing such as
• 3 w/w where w is short for weight (mass)

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Calculation

• Calculate the mass percentage of NaCl in a
  solution containing 1.50 g of NaCl in 50.0 g of
  water.

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You Try

• A Commercial bleaching solution contains 3.62
  mass sodium hypochlorite, NaOCl. What is the
  mass of NaOCl in a bottle containing 2500 g of
  bleaching solution?

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Parts per million

• Percentage refers to parts in 100. Thus 3 means
  3 parts solute in 100 parts of solution.
• Parts per million 1 ppm contains 1 gram of
  solute per 1 million grams solution.

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Parts per million

• A solution has a Ag ion concentration of 3 ppm
• 3 g Ag in 1,000,000 g of solution
• 3 mg Ag in 1,000 g of solution
• 1,000 g of water solution has a volume of
  approximately 1 litre
• So, our solution has 3 mg Ag / litre
• ppm is approximately the same as mg/L

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Calculation

• A 2.5 g sample of groundwater was found to
  contain 5.4 ?g of Zn2. What is the concentration
  of Zn2 in ppm?

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Molality

• Molality (m) moles of solute per kilogram of
  solvent

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Molality
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Molarity
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Calculation

• A solution is made containing 7.5 g CH3OH in 245
  g H2O.
• Calculate the mole fraction
• Calculate the molality
• Calculate the mass

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Calculation

• Ascorbic Acid, (vitamin C, C6H8O6) is a
  water-soluble vitamin. A solution containing 80.5
  g of ascorbic acid dissolved in 210 g of water
  has a density of 1.22 g/ml at 55 C. Calculate a)
  mass percentage
• b) mole fraction
• c) molality
• d) molarity

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Calculation

• The density of toluene (C7H8) is 0.867 g/ml, and
  the density of thiophene (C4H4S) is 1.065 g/ml. A
  solution is made by dissolving 10.0 g of
  thiophene in 250.0 ml of toluene.
• a) Calculate the mole fraction of thiophene
• b) calculate the molality of thiophene

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Calculation

• Caffeine (C8H10N4O2) is a stimulant found in
  coffee and tea. If a solution of caffeine in
  chloroform (CHCl3) as a solvent has a
  concentration of 0.0750 m calculate
• a) caffeine by mass
• b) mole fraction of caffeine

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Colligative Properties

• Properties that depend on solute concentration
  (quantity) not the kind of solute
• Lowering the vapor pressure
• Freezing Point Depression
• Boiling-Point Elevation
• Osmosis

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09_10.jpg
Lowering the Vapor Pressure
Why do you think the liquid levels in the two
beakers change over time?
Seawater
Distilled Water
Seawater
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Lowering the Vapor Pressure

• Addition of a nonvolatile solute lowers the vapor
  pressure of the solvent
• Extent of lowering depends on concentration of
  solute, described by Raoults Law
• Raoults Law The equilibrium vapor pressure of
  the solvent over the solution is directly
  proportional to the mole fraction of the solvent
  in the solution
• Psolvent XsolventPsolvent

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Lowering the Vapor Pressure

• Glycerin (C3H8O3) is a nonvolatile
  non-electrolyte with a density of 1.26 g/ml at 25
  C. Calculate the vapor pressure at 25 C of a
  solution made by adding 50.0 ml of glycerin to
  500.0 ml of water. (The vapor pressure of pure
  water at 25 C is 23.8 torr.)

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Conceptual Question

• A 0.100 m solution of which one of the following
  solutes in water will have the lowest vapor
  pressure?
• KClO4
• Ca(ClO4)2
• Al(ClO4)3
• Sucrose
• NaCl

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What does this say about the boiling point of the
soltuion?
At the Normal Boiling Point of a pure liquid,
vapor pressure of solution is lt 1 atm.
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Boiling-Point Elevation
The boiling point of a solution is higher than
that of a pure liquid
Animation
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Freezing Point Depression

• The freezing point of a solution is lower than
  that of a pure solvent

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Boiling-Point Elevation and Freezing Point
Depression

• Boiling Point Elevation
• dircetly proportional to the molality of the
  solute
• DTb Kb msolute
• Kb is a constant, m is molality
• Freezing Point Depression
• DTf Kf msolute
• Kf is a constant, m is molality

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Calculations

• The concentration of table sugar in a sucrose
  solution is 0.50 m. Calculate the freezing-point
  for this solution. (Kf of water is 1.86 C/m)

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More Calculations

• An environmentally concerned graduate student
  adds the more earth-friendly coolant, propylene
  glycol (C3H3O2, density 1.038) to her cars
  radiator, resulting in a final composition of her
  radiator fluid equaling 30 (v/v) ethylene glycol
  (C2H6O2, d1.114 g/ml) and 20 (v/v) propylene
  glycol in water. At what temperature will her
  engine boil over? (Kb 0.50 C/m)

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Conceptual Question

• Which of the following will have the lowest
  freezing point?
• Pure H2O
• Aqueous glucose (0.60 m)
• Aqueous sucrose (0.60 m)
• Aqueous FeI3 (0.24 m)
• Aqueous KF (0.50 m)

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Osmosis

• Why do red blood cells sometimes either shrivel
  or rupture?

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Osmosis

• The net movement of solvent through a
  semi-permeable membrane from a dilute to a more
  concentrated solution.

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Osmosis

• Eventually the pressure difference between the
  arms stops osmosis.

Animation
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Osmosis

• Osmotic pressure(?) - The pressure required to
  stop osmosis
• M - molarity of the solution
• R - gas constant (0.08206 L(atm)/mol(K))
• T - temperature in Kelvin

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Osmosis through the semi-permeable membrane of a
red blood cell
having the same osmotic pressure
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Osmosis through the semi-permeable membrane of a
red blood cell
having a higher osmotic pressure
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Osmosis through the semi-permeable membrane of a
red blood cell
having a lower osmotic pressure
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Osmosis

• The average osmotic pressure of blood is 7.7 atm
  at 25 C. What concentration of glucose (C6H12O6)
  will be isotonic with blood?

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Fractional Distillation of Benzene and Toluene
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Fractional Distillation of Benzene and Toluene
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Fractional Distillation of Benzene and Toluene
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