Chapter 6: Solutions, Acids, And Bases Goss

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SOLUTIONS
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Solutions (ch.16)

• Solution a homogeneous mixture of pure
  substances
• The SOLVENT is the medium in which the SOLUTES
  are dissolved. (The solvent is usually the most
  abundant substance.)
• Example
• Solution Salt Water
• Solute Salt
• Solvent Water

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READ ONLY SECTION

• HOW DO SUBSTANCES DISSOLVE?
• According to the kinetic theory, the water
  molecules in each glass of tea are always moving.
  Some moving water molecules collide with sugar
  crystals. When this happens, energy is
  transferred to the sugar molecules at the surface
  of the crystal. (Holt, p. 192)

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The process of dissolution is favored by

• A decrease in the energy of the system
  (exothermic)
• 2) An increase in the disorder of the system
  (entropy)

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Liquids Dissolving in Liquids

• Liquids that are soluble in one another (mix)
  are MISCIBLE.
• LIKE dissolves LIKE
• POLAR liquids are generally soluble in other
  POLAR liquids.
• NONPOLAR liquids are generally soluble in other
  NONPOLAR liquids.

LIKE DISSOLVES LIKE demo
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Factors affecting rate of dissolution think iced
tea vs. hot tea the type of sugar you use
cubes or granulated

• 1) Surface area / particle size
• Greater surface area, faster it dissolves
• 2) Temperature
• Most solids dissolve faster _at_ higher temps
• 3) Agitation
• Stirring/shaking will speed up dissolution

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Saturation a solid solute dissolves in a solvent
until the soln is SATURATED

• Unsaturated solution is able to dissolve more
  solute
• Saturated solution has dissolved the maximum
  amount of solute
• Supersaturated solution has dissolved excess
  solute (at a higher temperature). Solid crystals
  generally form when this solution is cooled.

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ROCK CANDY, YUM!!

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Applying Concepts QUESTION

• When the crystallization has stopped, will the
  solution be saturated or unsaturated?
• ? answer

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ANSWER SATURATED

• Solution has the maximum amount of solute for a
  given quantity of solvent at a constant
  temperature and pressure.

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SOLUBILITY

• Solubility the amount of solute that will
  dissolve in a given amount of solvent

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Factors Affecting Solubility

• The nature of the solute and solvent different
  substances have different solubilities
• Temperature many solids substances become more
  soluble as the temp of a solvent increases
  however, gases are less soluble in liquids at
  higher temps.
• Pressure Only affects the solubility of gases.
  As pressure increases, the solubility of gases
  increases.

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Gases solubility

• Temp and Pressure (think flat soda)
• DEMO mentos in Diet Coke
• Nucleation site the following factors that
  contribute to the
  bubble formation
• Diet coke
• carbon dioxide is what makes the
  bubbles form in the
  first place
• in synthetic mixtures aspartam, caffeine
  and potassium
  benzoate where shown
  give better fountains
• Mentos
• the most important property is the rough surface
  which provides plenty of nucleation sites for
  bubble formation
• the density makes them sink which is ideal as the
  bubbles formed at the bottom of the bottle help
  expel much more soda
• mentos contains gelatin and gum arabic which
  could also reduce surface tension

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STOP
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Concentration of Solution

• Concentration refers to the amount of solute
  dissolved in a solution.

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MOLARITY
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Example Describe how you would prepare 2.50 L of
0.665 M Na2SO4 solution starting witha) solid
Na2SO4b) 5.00 M Na2SO4
Dissolve 236 g of Na2SO4 in enough water to
create 2.50 L of solution.
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MOLARITY BY DILUTION

• When you dilute a solution, you can use this
  equation

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Example Describe how you would prepare 2.50 L of
0.665 M Na2SO4 solution starting witha) 5.00 M
Na2SO4
Add 0.333 L of Na2SO4 to 2.17 L of water.
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Example Describe how you would prepare 2.50 L of
0.665 M Na2SO4 solution starting withb) solid
Na2SO4
Dissolve 236 g of Na2SO4 in enough water to
create 2.50 L of solution.
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MASS PERCENT
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MASS PERCENT

• Example What is the percent of NaCl in a
  solution made by dissolving 24 g of NaCl in 152 g
  of water?

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MOLALITY
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MOLALITY

• Example What is the molality of a solution that
  contains 12.8 g of C6H12O6 in 187.5 g water?

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MOLALITY

• Example How many grams of H2O must be used to
  dissolve 50.0 g of sucrose to prepare a 1.25 m
  solution of sucrose, C12H22O11?

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Colligative Properties of Solutions (chapter 16)

• Colligative properties physical properties of
  solutions that depend on the of particles
  dissolved, not the kind of particle.

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Colligative Properties

• Lowering vapor pressure
• Raising boiling point
• Lowering freezing point
• Generating an osmotic pressure

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2 to focus on

• Lowering vapor pressure
• Raising boiling point
• Lowering freezing point
• Generating an osmotic pressure

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Boiling Point Elevation

• a solution that contains a nonvolatile solute has
  a higher boiling pt than the pure solvent the
  boiling pt elevation is proportional to the of
  moles of solute dissolved in a given mass of
  solvent.

Like when adding salt to a pot of boiling water
to make pasta ?
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Boiling Point Elevation

• ?Tb kbm
• where ?Tb elevation of boiling pt
• m molality of solute (mol solute/kg solvent)
• kb the molal boiling pt elevation constant
• kb values are constants see table 16.3 pg. 495
• kb for water 0.52 C/m

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Ex What is the normal boiling pt of a 2.50 m
glucose, C6H12O6, solution?

• normal implies 1 atm of pressure
• ?Tb kbm
• ?Tb (0.52 ?C/m)(2.50 m)
• ?Tb 1.3 ?C
• Tb 100.0 ?C 1.3 ?C 101.3 ?C

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Freezing/Melting Point Depression

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

Like when salting roads in snowy places so the
roads dont ice over or when making ice cream ?
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Freezing/Melting Point Depression

• ?Tf kfm
• where ?Tf lowering of freezing point
• m molality of solute
• kf the freezing pt depression constant
• kf for water 1.86 C/m
• kf values are constants
• see table 16.2 pg. 494

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Ex Calculate the freezing pt of a 2.50 m glucose
solution.

• ?Tf kfm
• ?Tf (1.86 ?C/m)(2.50 m)
• ?Tf 4.65 ?C
• Tf 0.00?C - 4.65 ?C -4.65?C

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Textbook pg. 495 34

• Calculate the freezing-point depression (?Tf) of
  a benzene solution containing 400. g of benzene
  and 200. g of acetone, C3H6O (solute).
• Kf for benzene is 5.12 C/m

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Answer

• ?Tf Kf x m
• ?Tf (5.12 C/m) x (m)
• m

So, ?Tf (5.12 C/m) x (8.61 m) 44.1 C
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Do the following on your paper

• 1. What is the boiling point of each solution?
• a) 0.50 mol glucose in 1000. g water
• b) 1.50 mol NaCl in 1000. g water
• 2. What is the freezing point of each solution?
• a) 1.40 mol Na2SO4 in 1750 g water
• b) 0.060 mol MgSO4 in 100. g water
• 
  ? answers

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ANSWERS

• 1a) 100.26 C
• 1b) 100.78 C
• 2a) -1.49 C
• 2b) -1.1 C

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More calcs.
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Ex When 15.0 g of ethyl alcohol, C2H5OH, is
dissolved in 750 grams of formic acid, the
freezing pt of the solution is 7.20C. The
freezing pt of pure formic acid is 8.40C.
Determine Kf for formic acid.

• ?Tf kfm
• 1.20 ?C (kf)( 0.4340 m)
• kf 2.76 ?C/m

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EXTRA NOTES

• Important info for lab, etc.

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Electrolytes and Colligative Properties

• Colligative properties depend on the of
  particles present in solution.
• Because ionic solutes dissociate into ions,
  they have a greater effect on freezing pt and
  boiling pt than molecular solids of the same
  molal conc.

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Electrolytes and Colligative Properties

• For example, the freezing pt of water is lowered
  by 1.86C with the addition of any molecular
  solute at a concentration of 1 m.
• Such as C6H12O6, or any other covalent compound
• However, a 1 m NaCl solution contains 2 molal
  conc. of IONS. Thus, the freezing pt depression
  for NaCl is 3.72Cdouble that of a molecular
  solute.
• NaCl ? Na Cl- (2 particles)

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Electrolytes - Boiling Point Elevation and
Freezing Point Depression

• The relationships are given by the following
  equations
• ?Tf kf mn or ?Tb kbmn
• ?Tf/b f.p. depression/elevation of b.p.
• m molality of solute
• kf/b b.p. elevation/f.p depression constant
• n particles formed from the dissociation of
  each formula unit of the solute

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Ex What is the freezing pt of a 1.15 m sodium
chloride solution?

• NaCl ? Na Cl- n2
• ?Tf kfmn
• ?Tf (1.86 ?C/m)(1.15 m)(2)
• ?Tf 4.28 ?C
• Tf 0.00?C - 4.28 ?C -4.28?C