lecture outline: chapter 13 review of solution terms p ti
TRANSCRIPT
Lecture outline: Chapter 13P ti f l tiProperties of solutions
Wh l i f h l l l l•Why solutions form at the molecular level
•Units of solution concentration
•Colligative properties: effects of solutes on BP, MP, and vapor pressure, , a d apo p essu e
•Osmotic pressure
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Review of solution terms• Solution: a homogeneous mixture of 2 or more
substances• Solvent: the component of the solution present in
greatest quantity• Solute: a substance dissolved in the solvent• Solubility: a term that refers to how much of a
solute can dissolve in a given solvent (grams solute dissolved/100 ml solution)Mi ibl t b t th t f l ti• Miscible: two substances that can form a solution at all solute-solvent proportions
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The solution process• “soluble” in water: glucose, NaCl, NaOH,
acetic acid, MgSO4 (“soluble” means aacetic acid, MgSO4 ( soluble means a significant amount can dissolve)
• “Insoluble” in water: CaCO AgCl C H I• Insoluble in water: CaCO3, AgCl, C6H14, I2(“insoluble” means a very little amount dissolves)dissolves)
• “miscible” with water: ethanol, glycerol, formaldehyde (“miscible” means soluble at allformaldehyde (“miscible” means soluble at all proportions)
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The solution processp• Why do some substances dissolve in water
while others don’t? Consider strengths of:while others don t? Consider strengths of:1. Solvent-solvent intermolecular forces (BREAK)2 Solute solute intermolecular forces (BREAK)2. Solute-solute intermolecular forces (BREAK)3. Solvent-solute intermolecular forces (solvation,
hydration) (FORM)hydration) (FORM)
Remember, it takes energy to break a bond or intermolecular attraction, while the formation of a new bond or intermolecular attraction releases energy
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Solvent (e.g. water)
5Solute (e.g. glucose)
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Sodium chloride dissolves in water to form hydrated sodium and choride ionsy
+
-
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Hydrated chloride and sodium ions: ion-di l tt tidipole attractions
Na+Cl-
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The dissolving process can be exothermic, endothermic, or “isothermic”,
• NaCl in water: ΔT ~ 0
• NaOH in water: ΔT > 0
• (NH )(CH COO) in water: ΔT < 0• (NH4)(CH3COO) in water: ΔT < 0
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Another term important in dictatingAnother term important in dictating whether a reaction occurs
“Entropy”
Thermodynamics chemistry 2: chemical reactionsThermodynamics, chemistry 2: chemical reactions that occur with an increase in the “disorder” (randomness) of the system are favored(randomness) of the system are favored
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Dynamic equilibrium: when two opposing processes occur at the same rate, so that there is no net change in the state of the system
Example 1: vapor pressure inExample 1: vapor pressure in a sealed container of water
rateescape = ratereturn
Example 2: a saturated psolution containing undissolved solute
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ratesolute dissolving = ratesolute crystallizing
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Factors affecting solubilityg y
•Nature of solute-solvent interactions•Nature of solute-solvent interactions
•Pressure
•Temperature
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Factors affecting solubilityg y
•Nature of solute-solvent interactions•Nature of solute-solvent interactions
•Pressure
•Temperature
“like dissolves like”polar + polarpolar + polarnonpolar + nonpolar
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What molecules dissolve in water? • soluble salts (ion-dipole interactions)
• polar moleculesH b di– H-bonding
– polar but no H-bonding
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Some polar molecules in water
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Solubility of alcohols in waterH
C O HH
H
C O H
H
C
H
H C O HC
HH
H
C O H
H
C
H
C
H
H
HHH
HHHH
15C O HC
HH
CC
H
H
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Small compounds with hydroxyl groups tend to dissolve in water Htend to dissolve in water• Glycerol (nontoxic) C O HH
C OH H
C
H
OH H
• Propylene glycol (nontoxic)C O H
H
H
C
C
H
OH
HH
H
• Ethylene glycol (highly toxic) H
C O H
H
H
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C OH H
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Glucose, C6H12O6
C
OH H
C
C OHOC
C
H
H
O
HH
C HO
C OHC
COO
OHHC
CH
H
H
H
C OH
C
H OH HH
H O HCH
H
O H
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nonpolar + nonpolar
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nonpolar + nonpolar
Cl H H H H H
CCl
ClCl
H C C
H H
C
H
C
H
C
H
H
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Mix solutions of CCl4 and H2O together:density, H2O ~ 1 g/ml
density, CCl4 ~ 1.6 g/mldensity, CCl4 1.6 g/ml
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Mix solutions of CCl and H OCCl4 and H2O together:
density, H2O ~ 1 g/ml
CC /density, CCl4 ~ 1.6 g/ml
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Mix solutions of CCl4 and H2O together:
density, H2O ~ 1 g/ml
density CCl ~ 1 6 g/mldensity, CCl4 ~ 1.6 g/ml
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If you added CuSO4 to the separatory funnel, thenseparatory funnel, then shook it, where would the CuSO end up?CuSO4 end up?
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If you added I2 to the separatory funnel, thenseparatory funnel, then shook it, where would the I2end up?end up?
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Gases in water
• N2
• CO• O2
• ArK• Kr
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Solubility data for some gases in water at 298 K
Molecule Mr structure Predominant intermolecular attraction with water
Solubility (g solute/kg H2O)
H2 2.02 H H London 0.0015
CH4 16.1 C
H
London 0.021CH4 16.1 CH
HH
London 0.021
N2 28 N N London 0.018
O2 32 O O London 0.039
CO2 44 C OO London 1.5
H2S SH
H
Dipole-dipole 3.3
SO2
OS
O
Dipole-dipole and hydrogen bonding 94
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NH3 NH
HH
Hydrogen bonding 470
Factors affecting solubilityg y
•Nature of solute-solvent interactions•Nature of solute-solvent interactions
•PressureHenry’s law constant for the gas sol ent pair
•Temperature
F C kP
gas-solvent pair at a defined temperature
For gases: Cg = kPg
Partial pressure of gas over
Solubility of gas in solution phase
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solution
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Dynamic equilibrium: when two i t thopposing processes occur at the
same rate, so that there is no net h i th t t f th tchange in the state of the system
•Example 1: vapor pressure in p p pa sealed container of water
E l 2 t t d•Example 2: a saturated solution containing ndissol ed sol teundissolved solute
•Example 3: the solubility of a
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p ygas in water
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Air: ~78% N2, 21% O2 by volume
Rateescape = rate return,O2 ,O2
Rateescape = rate return,N2 ,N2
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What is the concentration of dissolved oxygen in a fresh-water stream in equilibrium with air at 25°C and 1 atm. P?k 1 66 10 6 M/ HkO2
= 1.66 x 10-6 M/mm HgXO2
= 0.21Cg = kPg
P1 = X1PT
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Examples of Henry’s law• Bottle of soda pop
• Scuba diving
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Examples of Henry’s law• Scuba diving
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Factors affecting solubilityg y
•Nature of solute-solvent interactions•Nature of solute-solvent interactions
•Pressure
•Temperature
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In general, but not always, the solubility of solid solutes increases with increasing temperature
The solubility of gases decreases with increasing temperature
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Units of solution concentration• Molarity molsolutemols• Molarity
• Molality
M==l
molsolution literssolute mols
l tl• Molality
M l f ti
m=solvent kg
solute mols
• Mol fraction
M %• Mass %
• Volume %
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• Parts per millionS. Ensign, solutions
The density of water changes as a f ti f t tfunction of temperature
Density of water at different temperatures
1.000
1.001
ty (g
/ml)
0.998
0.999
dens
it
0.997
0 5 10 15 20 25 30 350.995
0.996
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temperature (°C)
0 5 10 15 20 25 30 35
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Density of water at different temperatures
Solution prepared at 25° C….Density of water at different temperatures
1.000
1.001
(g/m
l)
0 998
0.999
dens
ity
0.997
0.998 1.00 l
0 5 10 15 20 25 30 350.995
0.996
temperature (°C)
0 5 10 15 20 25 30 35
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Density of water at different temperatures
Solution cooled to 25° C….Density of water at different temperatures
1.000
1.001
(g/m
l)
0 998
0.999
dens
ity
0.997
0.998 1.00 l
0 5 10 15 20 25 30 350.995
0.996
temperature (°C)
0 5 10 15 20 25 30 35
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Units of solution concentration• Molarity molsolutemols• Molarity
• Molality
M==l
molsolution literssolute mols
l tl• Molality
M l f ti
m=solvent kg
solute mols
• Mol fraction
M %t
11 n
nx =
Af• Mass % 100 x mass total
Aof massA % mass =
• Volume % v/v; m/v
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• Parts per million 610 x mass total
A of massA ppm =S. Ensign, solutions
Units of solution concentration (cont.)• Parts per million• Parts per million
610A of massAppm x= 10 mass total
A ppm x=
⎞⎛ 610 totalg
A g x⎟⎟⎠
⎞⎜⎜⎝
⎛
⎠⎝
⎟⎞
⎜⎛
⎟⎞
⎜⎛
⎟⎞
⎜⎛ g 1000mg 1000A g
⎟⎟⎠
⎜⎜⎝
⎟⎟⎠
⎜⎜⎝
⎟⎟⎠
⎜⎜⎝ kg 1
g 1g
g totalgg xx
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Units of solution concentration (cont.)• When the units of a solution are expressed in units of• When the units of a solution are expressed in units of
“mg/kg”, they are already expressed in units of ppm, so you don’t have to multiply by 106 anymore!y p y y y
610 totalg
A gA ppm x=solutionkg
A mg A ppm = totalg solutionkg
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Units of solution concentration (cont.)• In dilute aqueous solutions• In dilute aqueous solutions,
density, H2O ~ 1g/ml = 1 kg/l
solutionmlA g
solutionliterA mg
solutionkgA mg A ppm μ
===solution mlsolutionliter solution kg
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What is the mass % (w/w) composition of a solution prepared by mixing 46 1of a solution prepared by mixing 46.1 grams ethanol with 162 grams water??
100 x mass total
A of massA % mass =
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What is the volume % (v/v) composition of a solution prepared by mixing 46.1 grams ethanol p p y g gwith 162 grams water?? dH2O = 1.0 g/ml
d = 0 79 g/mldethanol = 0.79 g/ml
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Sodium hydrogen sulfite, NaHSO3, is used to adjust the pH of swimming pools. What is the concentration of Na+ ion in ppm in a 110,000 gallon (4.5 x 105 liter) swimming pool to which 560 grams NaHSO3 was added?
solution mlA g
solutionliter A mg
solution kgA mg A ppm μ
===
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Colligative properties: the effects of solute concentration on the properties of a solution•Vapor pressure lowering
•Boiling point elevation (raising)•Boiling point elevation (raising)
•Freezing point depression (lowering)
•Osmosis and osmotic pressure
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Vapor pressure lowering
Add solute
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47Equilibrium in pure water Equilibrium
reestablishedratecapture > rateescape
The extent of vapor pressure lowering is proportional to the concentration of solute particlesthe concentration of solute particles
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Vapor pressure loweringMol fraction of solvent
Raoult’s law: PA = XAP°ARaoult s law: PA XAP A
VaporVapor pressure of pure solvent
Vapor pressure of solution
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What is the vapor pressure at 25°C above a solution that contains 46 grams of sucrose in 355 ml of water? The vapor pressure of pure water at 25°C is 23 8 torrThe vapor pressure of pure water at 25 C is 23.8 torr.
Raoult’s law: PA = XAP°A
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Colligative properties: the effects of solute concentration on the properties of a solution•Vapor pressure lowering
•Boiling point elevation (raising)•Boiling point elevation (raising)
•Freezing point depression (lowering)
•Osmosis and osmotic pressure
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Boiling point elevation (raising)
Molal conc. of solute
ΔTb = Kbm
of solute particles
ΔTb KbmMolal-boiling pointChange in boiling
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point elevation constant
point from pure solvent
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Boiling point elevation
For H2O, Kb = 0.52° C/m
Molal conc.
ΔT = K m
of solute particles
ΔTb = KbmMolal-boiling
Ch i b ilig
point elevation constant
Change in boiling point from pure solvent
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Colligative properties: the effects of solute concentration on the properties of a solution•Vapor pressure lowering
•Boiling point elevation (raising)•Boiling point elevation (raising)
•Freezing point depression (lowering)
•Osmosis and osmotic pressure
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Freezing point depression (lowering): molecular explanationp
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Equilibrium between ice and liquid water at 0 °C
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Ratemelting = ratefreezing
Addition of a solute to ice and liquid water at 0 °C
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Ratemelting > ratefreezing
The ice dissolves if temperature stays 0 °C
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Ratemelting > ratefreezing
Lowering the temperature below 0 °C slows rate of melting allowing equilibrium to be reestablishedg g q
Melting is endothermic,freezing is exothermicfreezing is exothermic
Δ
solidliquid
Δoutfreezing
solidliquid
Δinmelting
59S. Ensign, solutionsRatemelting = ratefreezing
Freezing point depression (lowering)
For H2O, Kf = 1.86° C/m
Molal conc. of solute
ΔTf = Kfm
of solute particles
ΔTf KfmMolal-boiling pointChange in
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point elevation constant
freezing point from pure solvent
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Colligative properties: the effects of solute concentration on the properties of a solution•Vapor pressure lowering
•Boiling point elevation (raising)•Boiling point elevation (raising)
•Freezing point depression (lowering)
•Osmosis and osmotic pressure
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Osmosis: The net movement of solvent across a semi-permeable membrane from the side with lower solute concentration to the side with higher solute concentration
The key to osmosis isThe key to osmosis is the semi-permeable membrane:
62S. Ensign, solutionswater solute
Separation of water on the sides of two glass tubes by the semi-permeable membraney p
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Water levels are equal on both sides
Addition of solute molecules to the left side slows rate of water movement from left to right, but not g ,
right to left
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Water levels become uequal
Equilibrium is established when sufficient pressure on the left side causes water to move p
between sides at the same rate
ΔhΔh
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Water levels at equilibrium dicated by osmotic pressure
Osmotic pressure: The pressure that must be applied on the side with higher solute pp g
concentration in order to prevent net movement of solvent molecules
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The membranes of cells are semipermeable membranessemipermeable membranes
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Figure Credit: LadyofHats, (Mariana Ruiz Villarreal )http://commons.wikimedia.org/wiki/File:Osmotic_pressure_on_blood_cells_diagram.svg
Some more solution terms•HydrophilicHydrophilic
•Hydrophobic
•Amphipathic
S /d t t•Soap/detergent
•MicelleMicelle
•Colloidal suspension
•macromolecule
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