Role of Disorder in Solutions

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Role of Disorder in Solutions
Ch 13 Solutions

• Disorder (Entropy) is a factor
• Solutions mix to form maximum disorder

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Two Ways to Form Solutions

• 1. Physical Dissolving (Solvation)
• NaCl(s) ? Na(aq) Cl-(aq)
• C12H22O11(s) ? C12H22O11(aq)
• Particles are surrounded by solvent molecules
• Can evaporate water/solvent to get original
  compound back

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Types of Reactions
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• Chemical reaction
• Ni(s) 2HCl(aq) ? NiCl2(aq) H2(g)
• Evaporating solvent gives the products

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• Solubility Maximum amount of a solute that can
  dissolve in 100 mL of a solution
• Ex NaCl 35.7 g/100mL
• Saturated solution Contains the max. amount of
  solute with some undissolved solid,
• Unsaturated more solute will dissolve.

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• Supersaturated More than the max is dissolved
  by heating and slowly cooling.

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Like Dissolves Like Miscibility

• Polar dissolves polar (dipole-dipole Forces) and
  ionic (iondipole)
• Water and Ammonia
• Non-Polar dissolves non-polar (London Forces)
• Soap and grease

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• Would acetone (shown below) dissolve in water?

O CH3CCH3
Acetone
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• Using you knowledge of like dissolves like,
  explain the following trends in solubility.

Alcohol Solubility in H2O (mol/100 g H2O at 20oC)
CH3OH 8
CH3CH2OH 8
CH3CH2CH2OH 8
CH3CH2CH2CH2OH 0.11
CH3CH2CH2CH2CH2OH 0.030
CH3CH2CH2CH2CH2CH2OH 0.0058
CH3CH2CH2CH2CH2CH2CH2OH 0.0008
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Pressure Effects

• Solubilty of a gas increases with pressure of gas
  over the liquid (soda bottle)
• Henrys Law
• Sgas kPgas

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Henrys Law

• The Henrys law constant for CO2 is 0.031
  mol/L-atm.
• Calculate the concentration of CO2 in a soda
  bottle pressurized to 4.00 atm of CO2.
• After the bottle has been opened, the
  concentration drops to 9.3 X 10-6 M. Calculate
  the partial pressure of CO2 over the soda.

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Temperature Effects

• Solubility of most solids increases with
  temperature
• Solubility of most gases decreases with
  temperature (warm soda)
• Warm water is deoxygenated
• Problem with thermal pollution of lakes

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Ways of Expressing Concentration

• Mass mass of compound in soln X 100
• total mass of soln
• Parts Per Million
• ppm mass of component X 106
• total mass of soln

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Concentration Ex 1

• 13.5 g of C6H12O6 is dissolved in 0.100 kg of
  water. Calculate the mass percentage.
• mass 13.5 g X 100 11.9
• (100 g 13.5 g)

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Concentration Ex 2

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

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Concentration Ex 2

• A 2.5 g sample of groundwater is found to contain
  5.4 mg of Zn2. What is the concentration of the
  Zn2 ion in ppm.
• 5.4 mg 1X10-6g 5.4 X 10-6 g
• 1 mg
• ppm mass of component X 106
• total mass of soln
• ppm 5.4 X 10-6 g X 106 2.2 ppm
• 2.5g

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Concentration Ex 3

• Calculate the mass percentage of NaCl in a
  solution containing 1.50 g of NaCl in 50.0 g of
  water.
• ANS 2.91

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Concentration Ex 4

• Bleach is 3.62 NaOCl. What mass of NaOCl is
  contained in 2500 g of bleach?
• ANS 90.5 g NaOCl

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Mole Fraction

• Mole Fraction
• X moles of component
• total moles of all components
• What is the mole fraction of HCl if 36.5 grams is
  dissolved in 144 grams of water?
• ANS 0.111

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Molality

• Molality moles of solute
• kilograms of solvent
• Why not use Molarity?
• Molarity varies with temperature
• Total volume of a solution changes with
  temperature (liquid expands)
• Mass does not change with temperature

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Molality Ex 1

• A solution is made by dissolving 4.35 grams of
  C6H12O6 in 25.0 mL of water. Calculate the
  molality of the glucose.
• 4.35 g 1 mol 0.0241 mol
• 180.2 g
• Molality 0.0241 mol 0.964 m
• 0.0250 kg

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Molality Ex 2

• Calculate the molality of a solution made by
  dissolving 36.5g C10H8 in 425 grams of toluene
  (solvent).
• ANS 0.671 m

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Molality Ex 3

• A solution of HCl contains 36 percent HCl by
  mass. Calculate the mole fraction and molality
  of HCl.
• Pretend 100 g
• 36 g HCl
• 64 g H2O

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• 36 g HCl 1 mol HCl 0.99 mol HCl
• 36.5 g HCl
• 64 g H2O 1 mol H2O 3.6 mol HCl
• 18 g H2O
• XHCl 0.99 mol HCl 0.22
• 0.99 mol 3.6mol
• Molality 0.99 mol HCl 15 m
• 0.064 kg H2O

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Molality Ex 4

• A commercial bleach solution contains 3.62
  percent NaOCl by mass. Calculate the mole
  fraction and molality of NaOCl.
• ANS XNaOCl 0.00900, 0.505 m

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Molality Ex 5

• The density of a solution of 5.0 g of toluene
  (C7H8) and 225 g of benzene (C6H6) is 0.876 g/mL.
  Calculate the molality and molarity of the
  toluene.

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Molality Ex 5

• The density of a solution of 5.0 g of toluene
  (C7H8) and 225 g of benzene (C6H6) is 0.876 g/mL.
  Calculate the molality and molarity of the
  solution.
• Molality
• 5.0 g 1 mol 0.054 mol
• 92.0 g
• m 0.054 mol/ 0.225 kg 0.24 m

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• Molarity
• D mass/V
• V mass/D
• V 230 g 263 mL
• 0.876 g/ml
• M 0.054 mol 0.21 M
• 0.263 L

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Molality Ex 6

• A solution containing equal masses of glycerol
  (C3H8O3) and water has a density of 1.10 g/mL.
  Calculate
• molality (10.9 m)
• mole fraction (XC3H8O3 0.163)
• molarity of glycerol in the solution (5.97 M)

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Colligative Properties Vapor Pressure Lowering

• Non-volatile solutes lower the vapor pressure of
  the solvent
• Raoults law
• PA XAPoA
• PA Vapor pressure
• XA Mole fraction of solvent
• PoA Pressure of pure solvent

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Raoults Law Ex 1

• What is the vapor pressure of a solution made by
  adding 50.0 mL of glycerin (C3H8O3) to 500.0 mL
  of water? The density of glycerin is 1.26 g/mL
  and the vapor pressure of pure water is 23.8
  torr.
• MassC3H8O3 (50.0 mL)(1.26 g/mL ) 63.0 g
• MolesC3H8O3 63.0 g/92.1 g/mol 0.684 mol
• MolesH2O 500.0 g/18 g/mol 27.8 mol

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• XH2O 27.8 mol 0.976
• (27.8 mol 0.684 mol)
• PA XAPoA
• PA (0.976)(23.8 torr) 23.2 torr

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Raoults Law Ex 2

• The vapor pressure of water at 110oC is 1070
  torr. A solution of ethylene glycol and water
  has a vapor pressure of 1 atm at 110oC. What is
  the mole fraction of ethylene glycol in the
  solution?
• ANS 0.290

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Colligative Properties Boiling Point Elevation

• Non-volatile solute raises the boiling point of a
  solution
• Shifts the phase diagram
• The pressure of the solution reaches atmospheric
  pressure at a higher temp.
• DTb iKbm

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Colligative Properties Freezing Point Depression

• Solutions freeze at a lower temperature than pure
  solvent
• Salt water freezes lower (-2oC) than distilled
  water (0oC)
• DTf iKfm
• i Vant Hoff factor
• m molality of the nonvolatile solute

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• The more ions produced, the greater the freezing
  point depression or boiling point elevation
• C12H22O11 (i1)
• NaCl Produces two ions (i2)
• CaCl2 Produces three ions (i3)

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Pure Solvent Solution
Boiling Point
Boiling Point
Freezing Point
Freezing Point
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Colligative Ex 1

• Ethylene Glycol, C2H6O2, is used in antifreeze.
  What will be the freezing and boiling point of a
  25.0 mass percent solution of ethylene glycol and
  water?
• Pretend 100 grams of solution
• 25 grams of C2H6O2
• 75 grams of H2O (0.075 kg)

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• 25 grams of C2H6O2 0.403 moles
• m 0.403 moles 5.37 m
• 0.075 kg H2O
• DTb iKbm (1)(0.52oC/m)(5.37 m) 2.8oC
• DTf iKfm (1)( 1.86oC/m)(5.37 m) 10.0oC
• Boiling Point 102.8oC
• Freezing Point -10.0oC

o
o
o
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Colligative Ex 2

• Calculate the freezing point of a solution
  containing 0.600 kg of CHCl3 and 42.0 g of
  C10H18O. Kf for CHCl3 is 4.68oC/m and the normal
  freezing point is -63.5 oC.
• ANS -65.6oC

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Colligative Ex 3

• Rank the following aqueous solutions in order of
  their expected freezing points
• 0.050 m CaCl2
• 0.15 m NaCl
• 0.10 m HCl
• 0.050 m HC2H3O2 (acetic acid)
• 0.10 m C12H22O11 (sugar)

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• 0.050 m CaCl2 (0.15 m in particles)
• 0.15 m NaCl (0.30 m in particles)
• 0.10 m HCl (0.20 m in particles)
• 0.050 m HC2H3O2 (just above 0.05 m)
• 0.10 m C12H22O11 (0.10 m in particles)
• Lowest FP Highest FP
• NaCl lt HCl lt CaCl2 lt C12H22O11 lt HC2H3O2

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Colligative Ex 4

• Rank the following in order of the increase in
  boiling point that they will produce in 1 kg of
  water
• 1 mol Co(NO3)2
• 2 mol KCl
• 3 mol C2H6O2 (a very, very weak
  electrolyte(acidic))

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• 1 mol Co(NO3)2 (3 mol particles)
• 2 mol KCl (4 mol of particles)
• 3 mol C2H6O2 (3 mol of particles)
• Lowest BP Highest BP
• Co(NO3)2 lt C2H6O2 lt KCl

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Freezing Pt Depression Ex 5

• What would be the molality of salt water if it
  freezes at 0 oF? Kf 1.86 oC/m.
• ANS 4.78 m

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Colligative Properties Osmotic Pressure

• Osmosis movement of solvent from high
  concentration to low concentration
• semipermeable membrane allows to passage of
  some particles but not others
• Cucumber Skin cell after
• in salt water soaking in a tub

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• Note that solvent moves both ways
• Solute too large to pass through membrane
• Net movement is to try to dilute the side with
  solutes

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• Osmotic Pressure (p) pressure required to
  prevent osmosis
• PV inRT
• V inRT
• p inRT
• V
• p iMRT
• M molarity

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Osmotic Pressure Ex 1

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

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Osmotic Pressure Ex 2

• What is the osmotic pressure at 20oC of a 0.0020
  M sucrose, C12H22O11, solution? Express your
  answer both in atmosphere and in torr.
• ANS 0.048 atm, 37 torr

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Molar Mass Ex 1

• A solution of an unknown nonelectrolyte was
  prepared by dissolving 0.250 g in 40.0 g of CCl4.
  The boiling point of the resulting solution was
  0.357oC higher than that of the pure solvent. Kb
  for CCl4 is 5.02 oC/m. Calculate the molar mass
  of the unknown.

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• DTb iKbm
• m DTb /iKb
• m (0.357oC)/(1 X 5.02 oC/m) 0.0711 m
• m mol of solute
• kilograms of solvent
• molsolute (m)(kg of solvent)
• molsolute (0.0711 m)(0.0400 kg) 0.00284 mol
• Molar Mass 0.250 g 88.0 g/mol
• 0.00284 mol

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Molar Mass Ex 2

• Camphor, C10H16O, melts at 179.8oC and has a Kf
  of 40.0 oC/m. When 0.186 g of an unknown
  substance is dissolved in 22.01 g of liquid
  camphor, the freezing point is 176.7oC. What is
  the molar mass of the solute?
• ANS 110 g/mol

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Molar Mass Ex 3

• A solution contains 3.50 mg of protein dissolved
  in water to form 5.00 mL of a solution. The
  osmotic pressure at 25oC was found to be 1.54
  torr. Calculate the molar mass of the protein.
• 1.54 torr 1 atm 0.00203 atm
• 760 torr

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• p iMRT
• M p/iRT
• M 0.00203 atm 8.28X10-5 M
• (1)(0.0821 L-atm/mol-K)(298)
• M moles
• liter
• moles (M)(liters) (8.28X10-5 M)(0.00500L)
• moles 4.14 X 10-7 mol
• Molar mass 3.50 X 10-3 g 8454 g/mol
• 4.14 X 10-7 mol

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Molar Mass Ex 4

• A 2.05 g sample of a plastic was dissolved in
  enough toluene to form 100 mL of solution. The
  osmotic pressure of this solution is 1.21 kPa at
  25oC. Calculate the molar mass of the plastic.
  (1 atm 101.325 kPa).
• ANS 42,000 g/mol

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Colloids
Solutions/ Homogeneous Colloids Suspensions/ Heterogeneous Mixture
Ions/Molecular size solute particles Medium particles (10 to 2000 Å) Larger particles (like dirt in water) 2 or more separate phases
Never separate Separates quickly
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• Examples
• Fog
• Smoke
• Whipped Cream
• Milk
• Tyndall effect scattering of light

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Stabilization of Colloids

• Hydrophobic/hydrophilic imf
• Biomolecules

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• Emulsifying agents
• Soap
• Sodium stearate(used to digest fats)

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• 6. Larger Noble gases have greater London Forces
  (greater dipole induced dipole forces)
• a) IonDipole b) Dipole induced dipole
• c) Hydrogen bonding
• (weakest) b lt c lt a (strongest)
• a) glucose (OHs allow h-bonding)
• b) sodium propionate (has an ion)
• c) HCl (small and polar)

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• S kP k S/P 1.38 X 10-3M/0.21 atm
• k 6.57 X 10-3 M/atm
• Partial Pressure of O2 at the higher elevation
• 650 torr 0.855 atm
• PO2 (0.855 atm)(0.21)
• PO2 0.180 atm
• S kP S(6.57 X 10-3 )(0.180 atm)
• S 1.18 X 10-3 M

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• 36a) 7.2 I2 b) 7.9 ppm Sr2
• 38a) 0.0285 b) 5.66 c) 0.638 m
• 40a) 0.125 M b) 0.140 M c) 0.630 M
• 42a) 4.34 m b) 3.1 g S8
• 44a) 27.7 b) 0.0377 c) 2.18 m
• d) 1.92 M
• 46a) 0.0439 b) 0.498 m c) 0.417 M
• 48a) 0.278 mol b) 6.25X10-5 mol c) 0.00329 mol
• 50a) 21.8 g b) 7.7 g/112.3g c) 209 g
• d) 11 mL of 6.0 M HCl
• 52) 15 M NH3

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• a) 222 torr b) 150 g
• 64. a) 0.75 b) 0.47
• 66. 10 sucrose lt 10 glucose lt 10 NaNO3
• 68. 0.030 m phenol lt KBr 0.040 m glycerin
• a) -115.2, 78.8 b) -78, 72.4
• c) -9.3, 102.6
• -18 oC
• 2.8 atm
• 180 g/mol
• 78. 380 g/mol

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• Write Net Ionic Equations for
• MgCO3(s) HNO3(aq) ?
• H2SO4(aq) 2KOH(aq) ?
• NaHCO3(aq) HCl(aq) ?
• A solution of nickel(II)sulfate is stored in a
  zinc coated bucket.
• Write the net ionic reaction that occurs.
• Suppose the nickel(II)sulfate was stored in a
  copper bucket. Would this be a better choice?
• Write the net ionic reaction that occurs between
  nickel(II)sulfate and barium nitrate.

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1. Lots of ice, little water
2. Stir and take temperature (2 min)
3. Add medicine cup of rock salt
4. Stir and take temperature (2 min)
5. Clean Up
6. Rinse Foam cup, medicine cup, and thermometer
7. Place in drying rack

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• A 80.5 g sample of ascorbic acid (C6H8O6) is
  dissolved in 210.0 grams of water. The resulting
  solution has a density of 1.22 g/mL.
• Calculate the molarity of the solution
• Calculate the molality of the solution.
• Calculate the freezing point of the solution.
  (Assume ascorbic acid is a very weak electrolyte,
  Kf 1.86 oC/m)
• Would you expect the solution to have a higher or
  lower vapor pressure than pure water?
• Calculate the vapor pressure of the solution if
  the vapor pressure of pure water is 17.5 torr.

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• Benzene (C6H6) freezes at 5.50 oC and has a Kf of
  5.12 oC/m. 50.0 grams of an unknown solute is
  dissolved in 100.0 g of benzene. The resulting
  solution freezes at -8.72 oC.
• Calculate the molality of the solution. (2.78 m)
• Calculate the molar mass of the solute. (180)
• Why is benzene a good choice for this experiment?
• Comment on the polarity of the unknown molecule.
• What is the hybridization of the carbon atoms in
  benzene?