Transcript Chapter 13 Properties of Solutions

Properties of Solutions
SC 132 CHEM 2
Chemistry: The Central Science
CM Lamberty
Homework

Chapter 13
14, 16, 18, 20
 22a, 24, 28, 30, 32, 34
 36, 38, 40, 42, 44, 46, 48, 50, 52, 54
 60, 64, 66, 68, 70, 72, 74, 76, 78, 86,
 89, 91, 98, 112
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The Solution Process
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The Effect of Intermolecular Forces
The Solution Process
LIKE DISSOLVES LIKE
Substances with similar types of intermolecular forces dissolve in each
other.
When a solute dissolves in a solvent, solute-solute interactions and solvent-solvent
interactions are being replaced with solute-solvent interactions. The forces must be
comparable in strength in order to have a solution occur.
Solvation: Interactions between solute and solvent molecules.
Hydration: when solvent is water
Intermolecular Forces in Solution
Predicting Solubilities in Different
Solvents
The Solution Process
DHsoln = DHsolute + DHsolvent + DHmix
in ionic salt-aqueous solutions:
DHsoln = DHlattice + DHhydration of ions
DHsoln < 0 means that solution formation is favored!
Why Oil and Water do not mix

Give an explanation for this phenomena
based on what we have just learned.
Sol’n Formation, Spontaneity & Entropy
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CCl4 and C6H14 dissolve at all proportions
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Similar bp, both nonpolar, similar forces
Spontaneity determined by
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Energy
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Distribution of each component
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generally if E content decreases, or exothermic
generally greater entropy
Entropy: the randomness or dispersal in
space of the system
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System is no longer ordered substances
Practice
Saturated Solutions and Solubility
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Crystallization
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Saturated
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Max. amt of solute that will dissolve in given amt of
solvent at specific temperature
Unsaturated
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Solution in equilibrium w/ undissolved solute
Solubility
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Solute particles reattaching to each other
Less solute than needed for saturated solution
Supersaturated
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More solute than needed for saturated solution
Factors Affecting Solubility
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Solute-Solvent Interactions
The stronger the attractions between solute
and solvent the greater the solubility
 Like dissolves like
 Miscible: mix in all proportions
 Immiscible: do not dissolve in one another
 Table 13.3 Sol of alcohols in water and hexane
 solute-solute, solute-solvent and solventsolvent
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Factors Affecting Solubility
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Pressure Effects
Solubilities of solids/liquids not affected
 Great effect on gases
 Solubility of gas increases in direct proportion
to is partial pressure above the solution
 Henry’s Law: Sg = kPg
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Sg is solubility of gas
K is Henry’s constant (solvent-solute pair dependent)
Pg is partial pressure of gas over the solution
Carbonated Beverages
Factors Affecting Solubility in Liquid
Solvents
Pressure
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Only relevant to Sgas
Sgas = kHPgas
Practice
Factors Affecting Solubility
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Temperature Effects
Solubility of most solid solutes in water
increases as the temperature of the solution
increases
 Solubility of gases in water decreases with
increasing temperature
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
Decreased O2 solubility result of thermal pollution
Factors Affecting Solubility in Liquid
Solvents
Temperature
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Ssolids increase w/temp
increase
Sgases decrease w/temp
increase
Solution Concentration
•
Measure of the proportion of a substance
in a mixture
–
–
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Units can always be expressed in fractions
Solute quantity is in numerator,
solvent/solution quantity is in denominator
When solving problems involving solution
concentration, use fraction representation
of concentration unit
UNITS, UNITS, UNITS!!!!
Ways of Experessing Concentration
Concentration Term
Mass percent (m %)
Parts per million
Parts per billion
Ratio
Mass of component in soln
Total mass of soln
Mass of component in soln
Total mass of soln
Mass of component in soln
Total mass of soln
X 100
X 106
X 109
Ways of Experessing Concentration
Concentration Term
Molarity (M)
Molality (m)
Parts by mass
Parts by volume
Mole fraction 
Ratio
amount (mol) of solute
volume (L) of solution
amount (mol) of solute
mass (kg) of solvent
mass of solute
mass of solution
volume of solute
volume of solution
amount (mol) of component
Total moles of all component
Interconverting Concentration Terms

To convert a term based on amount (mol) to one
based on mass, you need the molar mass. These
conversions are similar to mass-mole
conversions.
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To convert a term based on mass to one based
on volume, you need the solution density.

Molality involves quantity of solvent, whereas the
other concentration terms involve quantity of
solution (solvent + solute).
Practice
Practice
PROBLEM:
Hydrogen peroxide is a powerful oxidizing agent used in
concentrated solution in rocket fuels and in dilute solution a a hair
bleach. An aqueous solution H2O2 is 30.0% by mass and has a
density of 1.11 g/mL. Calculate its
(a) Molality
PROBLEM:
(b) Mole fraction of H2O2
(c) Molarity
A sample of commercial concentrated hydrochloric acid is 11.8M and
has a density of 1.190g/mL. Calculate its
(a) Molality
(b) Mole fraction of H2O2
(c) Mass %
Colligative Properties of Solutions
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4 properties for which only the amount of
solute particles affect values, not
chemical identity of solute
Vapor pressure lowering → DP = XAP°A
 Boiling point elevation → DTb = kbm
 Freezing point depression → DTf = kfm
 Osmotic pressure →  = MRT
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UNITS, UNITS, UNITS!!!!!
Colligative Properties of Electrolyte
Solutions
DP, DTf, DTb, and  are always greater for
an electrolyte solution with the same
concentration as a nonelectrolyte one
 This is because electrolyte solutions
dissociate into separate pieces making the
apparent solution concentration greater
 Deviations from expected values can be
quantified by the van’t Hoff factor, i
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Practice
PROBLEM: Calculate the vapor pressure lowering, DP, of a solution of 2.00g of
aspirin (MM-180.15 g/mol) in 50g of methanol (CH3OH) at 21.2°C.
Pure methanol has a vapor pressure of 101 torr at this temperature.
PROBLEM: You add 1.00 kg of ethylene glycol (C2H6O2) antifreeze to your car
radiator which contains 4450g H2O. What are the boiling points and
freezing points of the solution? (kf = 1.86°C/m and kb = 0.512°C/m for
water)
PROBLEM: How many grams of NaCl must be added to a 5.00 gallon bucket filled
with water (d = 1.00g/mL) to prevent the water from freezing at -10°C
(kf = 1.86°C/m for water)
PROBLEM: A physician studying a particular variant of hemoglobin associated
with sickle cell anemia must first determine its molar mass, which
she will do by measuring its osmotic pressure. She dissolves 21.5mg
of hemoglobin in water at 5.0°C to make 1.50mL of solution and
measures an osmotic pressure of 3.61 torr. What is the molar mass
of this variety of hemoglobin
Practice
PROBLEM:
A 0.952-g sample of magnesium chloride is dissolved in 100. g of
water in a flask.
(a) Which scene depicts the solution best?
(b) What is the amount (mol) represented
by each green sphere?
(c) Assuming the solution is ideal, what is its freezing point (at 1 atm)?
PROBLEM:
The MgCl2 in the above problem has a density of 1.006g/mL at
20.0°C. What is the osmotic pressure of the solution?
Colloids
Intermediate type of dispersion or
suspension
 Dividing line between solutions and
heterogeneous solutions
 Size of dispersed particle 5-1000nm
 May be several atoms/ions or one large
one
 Scatter light
 Homogenized milk
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Colloids
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Hydrophilic and Hydrophobic Colloids
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Hydrophilic (water loving)
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Hemoglobin, enzymes and antibodies
Molecules fold so that hydrophobic groups on inside
away from water
Hydrophobic (water fearing)
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Must be stabilized in water
Adsorption of ions on sfc
Oil slick on water
Bile from gallbladder helps digest fats (emulsify the
fat)
Colloids
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Removal
Filtration will not work
 Coagulation: process by which the particles
clump together
 Semipermeable membranes
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Dialysis