Properties of Solutions

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Properties of Solutions

• Chapter 11

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Solutions

• . . . the components of a mixture are uniformly
  intermingled (the mixture is homogeneous).

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Solution Composition

• 1. Molarity (M)
• 2. Mass (weight) percent
• 3. Mole fraction (?A)
• 4. Molality (m)

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Molarity Calculations
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Mass Calculations
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Mole Fraction
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Molality Calculations
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Molarity Molality

• For dilute solutions, molarity (M) and
  molality(m) are very similar.
• In previous example, M 0.215 M and m 0.217 m.

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Normality

• Acid-Base Equivalents (moles) (total ()
  charge)
• Redox Equivalents (moles)( e- transferred)

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Normality Calculations

• .250 M H3PO4 ______N
• N M(total() charge)
• N (0.250)(3)
• N 0.750 N H3PO4

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Concentration Density Calculations

• See Example 11.2 on pages 517-518.
• Know how to do this problem!!

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Steps in Solution Formation

• Step 1 - Expanding the solute (endothermic)
• Step 2 - Expanding the solvent (endothermic)
• Step 3 - Allowing the solute and solvent to
  interact to form a solution (exothermic)
• ?Hsoln ?Hstep 1 ?Hstep 2 ?Hstep 3

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Three steps of a liquid solution 1) expanding
the solute, 2) expanding the solvent, 3)
combining the expanded solute and solvent to form
the solution.
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a) ?Hsoln is negative and solution process is
exothermic. b) ?Hsoln is positve and solution
process is endothermic.
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Processes that require large amounts of energy
tend not to occur. Solution process are favored
by an increase in entropy.
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Structure Solubility

• Like dissolves like.
• Hydrophobic --water-fearing. Fat soluble
  vitamins such as A, D, E, K.
• Hydrophilic --water-loving. Water soluble
  vitamins such as B C.
• Hypervitaminosis--excessive buildup of vitamins
  A, D, E, K in the body.

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Henrys Law
The amount of a gas dissolved in a solution is
directly proportional to the pressure of the gas
above the solution.

• P kC
• P partial pressure of gaseous solute above the
  solution
• C concentration of dissolved gas
• k a constant

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Solubility of several solids as a function of
temperature.
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The solubility of various gases at
different temperatures.
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When an aqueous solution and pure water are in a
closed environment, the water is transferred to
the solution because of the difference in vapor
pressure.
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Raoults Law
The presence of a nonvolatile solute lowers the
vapor pressure of a solvent.

• Psoln ?solventP?solvent
• Psoln vapor pressure of the solution
• ?solvent mole fraction of the solvent
• P?solvent vapor pressure of the pure solvent

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Raoults Law Calculations

• Sample Exercise 11.6 on page 532.
• Na2SO4 forms 3 ions so the number of moles of
  solute is multiplied by three.
• Psoln ?waterP?water
• Psoln (0.929)(23.76 torr)
• Psoln 22.1 torr

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Vapor pressure for a solution of two volatile
liquids. a) Ideal(benzene toluene) -- obeys
Raoults Law, b) Positive deviation (ethanol
hexane) from Raoults Law, c) Negative
deviation (acetone water). Negative deviation
is due to hydrogen bonding.
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Liquid-Liquid Solutions

• Ptotal PA PB
• ?APoA ?BPoB

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Raoults Law Calculations

• Sample Exercise 11.7 on page 535.
• ?A nA/(nAnC)
• ?A 0.100 mol/(0.100 mol 0.100 mol)
• ?A 0.500 ? ?C 0.500
• Ptotal ?APoA ?CPoC
• Ptotal (0.500)(345 torr) (0.500)(293 torr)
• Ptotal 319 torr

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Colligative Properties

• Depend only on the number, not on the identity,
  of the solute particles in an ideal solution.
• Boiling point elevation
• Freezing point depression
• Osmotic pressure

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Phase diagrams for pure water and for an aqueous
solution containing a nonvolatile solute --
liquid range is extended for the solution.
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Boiling Point Elevation

• A nonvolatile solute elevates the boiling point
  of the solvent. The solute lowers the vapor
  pressure of the solution.
• ?T Kbmsolutei
• Kb molal boiling point elevation constant
• m molality of the solute
• i vant Hoff factor ( ions formed)

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Boiling Point Calculations

• Sample Exercise 11.8 on page 537.
• ?T Kbmsolutei
• msolute ?T/(Kbi)
• msolute (0.34 Co)/(0.51 Cokg/mol)(1)
• msolute 0.67 mol/kg

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Boiling Point Calculations(Continued)

• msolute nsolute/ kgsolvent
• nsolute msolute kgsolvent
• nsolute (0.67 mol/kg)(0.1500 kg)
• nsolute 0.10 mol

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Boiling Point Calculations(Continued)

• n m/M
• M m/n
• M 18.00 g/0.10 mol
• M 180 g/mol

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Freezing Point Depression

• A nonvolatile solute depresses the freezing point
  of the solvent. The solute interferes with
  crystal formation.
• ?T Kfmsolutei
• Kf molal freezing point depression constant
• m molality of the solute
• i vant Hoff factor ( ions formed)

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Freezing Point Calculations

• Sample Exercise 11.10 on page 539.
• ?T Kfmsolutei
• msolute ?T/(Kfi)
• msolute (0.240 Co)/(5.12 Cokg/mol)(1)
• msolute 4.69 x 10-2 mol/kg

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Freezing Point Calculations(Continued)

• msolute nsolute/ kgsolvent
• nsolute msolute kgsolvent
• nsolute (4.69 x 10-2 mol/kg)(0.0150 kg)
• nsolute 7.04 x 10 -4 mol

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Freezing Point Calculations(Continued)

• n m/M
• M m/n
• M .546 g/7.04 x 10-4 mol
• M 776 g/mol

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Osmotic Pressure

• Osmosis The flow of solvent into the solution
  through the semipermeable membrane.
• Osmotic Pressure The excess hydrostatic
  pressure on the solution compared to the pure
  solvent.

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Due to osmotic pressure, the solution is diluted
by water transferred through the semipermeable
membrane. The diluted solution travels up the
thistle tube until the osmotic pressure is
balanced by the gravitational pull.
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Osmosis

• The solute particles interfere with the passage
  of the solvent, so the rate of transfer is slower
  from the solution to the solvent than in the
  reverse direction.

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a) The pure solvent travels at a greater rate
into the solution than solvent molecules can
travel in the reverse direction. b) At
equilibrium, the rate of travel of solvent
molecules in both directions is equal.
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Osmotic Pressure

• ? MRT
• ? osmotic pressure (atm)
• M Molarity of solution
• R 0.08206 Latm/molK
• T Kelvin temperature

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Osmotic Pressure Calculations

• Sample Exercise 11.11 on pages 541-542.
• ? MRT
• M ?/RT
• M (1.12 torr)(1 atm/760 torr)/(0.08206
  Latm/molK)(298K)
• M 6.01 x 10-5 mol/L

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Osmotic Pressure CalculationsContinued

• Molar Mass (1.00 x 10 -3g/1.00 mL)(1000 mL/1
  L)(1 L/6.01 x 10-5 mol)
• 1.66 x 104 g/mol protein

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Crenation Lysis

• Crenation-solution in which cell is bathed is
  hypertonic (more concentrated)-cell shrinks.
  Pickle, hands after swimming in ocean. Meat is
  salted to kill bacteria and fruits are placed in
  sugar solution.
• Lysis-solution in which cell is bathed is
  hypotonic (less concentrated)-cell expands.
  Intravenous solution that is hypotonic to the
  body instead of isotonic.

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• If the external pressure is larger than the
  osmotic pressure, reverse osmosis occurs.
• One application is desalination of seawater.

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Colligative Properties of Electrolyte Solutions
vant Hoff factor, i, relates to the number of
ions per formula unit. NaCl 2, K2SO4 3

• ?T mKi
• ? MRTi

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Electrolyte Solutions

• The value of i is never quite what is expected
  due to ion-pairing. Some ions stay linked
  together--this phenomenon is most noticeable in
  concentrated solutions.

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Osmotic Pressure Calculation for Electrolyte

• Sample Exercise 11.13 on page 548.
• Fe(NH4)2(SO4)2 produces 5 ions.
• ? MRTi
• i ? /MRT
• i 10.8 atm/(0.10 mol/L)(0.08206
  Latm/molK)(298 K)
• i 4.4

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Colloids

• Colloidal Dispersion (colloid) A suspension of
  tiny particles in some medium.
• aerosols, foams, emulsions, sols
• Coagulation The addition of an electrolyte,
  causing destruction of a colloid. Examples are
  electrostatic precipitators and river deltas.

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The eight types of colloids and examples of each.
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Tyndall Effect

• The scattering of light by particles of a colloid
  is called the Tyndall Effect. Which of the
  glasses below contains a colloid?

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Calorimeter Problem

• Add this problem to the Chapter 11 set of
  problems. KNOW how to work this problem--show
  the appropriate formula!!
• When 8.50 g of sodium nitrate is dissolved in
  600. g of water, the temperature of the solution
  rises 0.817 Co. What is the molar heat of
  solution for sodium nitrate?