Chapter 9 Lecture
Fundamentals of General,
Organic, and Biological
Chemistry
7th Edition
McMurry, Ballantine, Hoeger, Peterson
Chapter Nine
Solutions
© 2013 Pearson Education, Inc.
9.1 Mixtures and Solutions
• Solution – homogeneous mixtures of molecules and ions
– Solvent – substance present in largest amount
– Solute(s) – other substance(s) in the solution
– Aqueous solution (aq) – solution with water as the
solvent
• Colloids are homogenous mixtures with particles
ranging in diameter 2-500 nm
– They scatter light
Recall that homogenous implies uniform mixing with the same
composition throughout.
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A colloid example is milk. It has tiny globules of fat dispersed
in the liquid. They are apparent under a microscope.
9.2 The Solution Process
A solution forms when the solvent-solute interaction forces are stronger than (or
at least comparable to) the solute-solute interaction forces.
If the solute-solute interactions are much stronger, the solute will not dissolve.
Tro, Chemistry: A Molecular
Approach
4
“Like Dissolves Like”
• Nonpolar compounds dissolve
in nonpolar solvents
– e.g. hexane or oil solvent
• Polar (and ionic) compounds
dissolve in polar solvents
– e.g. salt and sugar in water
– Solute hydrogen bonding also
contributes to water solubility
• Review polarity from Ch 4!
– Small asymmetric molecules are
polar, and thus water soluble
Recall each water
molecule makes 4
hydrogen bonds to other
water molecules. The oil
is “squeezed out” of the
aqueous phase.
Pure hydrocarbons (C & H only)
• The above large pure hydrocarbons follow their smaller
cousins like methane, in being nonpolar
– Review London dispersion forces and IMFs from Ch 8!
• Large polar molecules typically have hydrogen bonding
sites…
Ethanol is miscible (soluble in any proportion)
with water due to the dominance of it’s own
polar OH bond
– An infinitely soluble substance is called miscible
– Ethanol’s miscibility is caused by the availability
of two hydrogen bonds per ethanol molecule
Glucose (C6H12O6) above is somewhat soluble in
water due to 6 hydrogen bonding sites (-OH). The
hydrocarbon “backbone” is, however, too large to be
[completely]
miscible with water.
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Solubility of Ionic Substances
• Ionic substances like NaCl break up into
individual cations and anions
– Cation (Na+) bonds to d- pole on water
– Anion (Cl-) bonds to d+ pole on water
• Solvation or hydration occurs when water
molecules form a large electrostatic shell around
each ion
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9.4 Solubility
• Miscible: Mutually soluble in all proportions
– Ethyl and methyl alcohols will continue to dissolve in
water no matter how much are added
• But most substances reach a solubility limit
beyond which no more will dissolve
• Solubility: The maximum amount of a substance
that will dissolve in a given amount of solvent at
a specified temperature
• Only 9.6 g baking soda dissolves in 100 mL water at
20 C
• Compared to 206 g sucrose under same conditions
• Saturated solution: Contains the maximum amount
of dissolved solute at equilibrium
– No more than 35.8 g of NaCl will dissolve in 100 mL of
water at 20 C
– Any amount above this limit sinks to the bottom of
the container as a solid
• A saturated solution is in a state of dynamic
equilibrium. Dissolution and crystallization occur at
the same nonzero rates.
9.5 Effect of Temperature on Solubility
• Temperature often has a dramatic effect on solubility,
but is very unpredictable
• In Intro, most solids become more soluble as
temperature rises, while the solubility of gases
always decreases
– but check out NaCl and Ce2(SO4)3
Extra info: supersaturated solutions
• Supersaturated solutions have
solute levels above the
equilibrium solubility level.
• Prepared by heating to increase
solubility and dissolution…
followed by cooling to lower
the equilibrium solubility level.
– Excess solute remains dissolved
(supersaturation)
– And precipitates dramatically
when disturbed
9.6 Pressure and Solubility: Henry’s Law
• c = kP at constant T
– Liquid conc (c) and gas pressure (P)
• It can also be explained using Le Châtelier’s principle
– When the system is stressed by increasing the
pressure of the gas, more gas molecules go into
solution to relieve the increased pressure
– When the pressure of the gas is decreased, more
gas molecules come out of solution to relieve the
decrease
Worked example 9.3
• At a partial pressure of oxygen in the atmosphere of
159 mmHg, the solubility of oxygen in blood is 0.44
g/100 mL.
• What is the solubility of oxygen in blood at 11,000 ft,
where the partial pressure of O2 is 56 mmHg?
• According to Henry’s law, the solubility of the gas
divided by its pressure is constant:
9.7 Units of Concentration
• 1) For solid solutions (eg, brass) concentrations are
typically expressed as mass/mass percent
concentration, (m/m)%:
mass of solute (g)
(m / m)% concentration =
 100%
mass of solution (g)
2) For liquid solutions, concentrations are expressed
as volume/volume percent concentration, (v/v)%:
volume of solute (mL)
(v / v)% concentration =
 100%
volume of solution (mL)
• 3) A third ‘percent’ method is to give the number of
grams of solute as a percentage of the number of
milliliters
– This is mass/volume percent concentration, (m/v)%:
Mass of solute (g)
(m / v)% concentration =
 100%
Volume of solution (mL)
• 4) Molarity (M) is used in chemistry. It represent the
moles of solute dissolved into total solution volume,
which includes both the solvent and the solute.
Moles of solute
Molarity (M) =
Liters of solution
9.8 Dilution
• Many solutions are stored in high concentrations and
then prepared for later use by dilution
• The amount of solute remains constant; only the
volume is changed by adding more solvent
• Because the number of moles remains constant, we
can set up the following dilution equation for
molarity:
M1V1 = M 2V2
Concentrated ammonia solution is available in
a 16.0 M solution. What volume must be used
to prepare 750.0 mL of a 2.0 M solution?
a.
b.
c.
d.
94 mL
43 mL
9.4 mL
4.3 mL
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9.9 Ions in Solution: Electrolytes
• Strong electrolytes are substances that ionize
completely when dissolved in water
– NaCl  Na+ (aq) + Cl- (aq)
– HCl  H+ (aq) + Cl- (aq)
• Weak electrolytes are substances that are only partly
ionized in water
– Eq shifted left toward CH3COOH (acetic acid)
• Nonelectrolytes are substances that do not produce
ions when dissolved in water
– C6H12O6 (Glucose)
– Water is a nonelectrolyte
• Ion levels are small (1 x 10-7 M) for pure water (sec 10.6)
Electrical conductivity of aqueous solutions
Many ions –
large current
Few ions –
weak current
No ions –
no current
9.10 Electrolytes in Body Fluids
• gram-equivalent (g-Eq) is a practical unit
– The amount of ions (in grams) that actually contains that
one mole of charge
• Ion(s) that have a +1 or −1 charge
– so 1 gram-equivalent of Na+ is simply 23.0 g
– so 1 gram-equivalent of Cl− is simply 35.4 g
• Ion(s) that have a +2 or −2 charge
– so 1 gram-equivalent of Mg2+ is (24.2/2) = 12.2 g
– so 1 gram-equivalent of S2− is (32.1/2) = 16.0 g
Note the narrow ranges for these electrolytes critical for
supporting human health.
Significant figures/rounding can have serious implications!!!
Worked Example 9.14
• The normal concentration of Ca2+ in blood is 5.0 mEq/L
– Clinical chemists use milliequivalents (1000 mEq = 1 Eq)
• How many milligrams of Ca2+ are in 1.00 L of blood?
9.12 Osmosis and Osmotic Pressure
• Osmosis: The passage of a solvent through a
semipermeable membrane separating two solutions
of different concentration.
𝜋 = 𝑀𝑅𝑇
– M = molar concentration (mol/L)
– R = universal gas const
– T = Kelvin temperature
• The osmotic pressure of a 0.15 M NaCl
solution at 25 °C is 7.3 atm
– It has units of pressure
• Osmotic pressure depends only on the
concentration of solute particles
• Osmolarity (osmol) is the sum of the
molarities of all dissolved particles in a
solution
• Osmosis is particularly important in living organisms
because the membranes around cells are
semipermeable. Water, but not larger molecules, passes
through the membrane.
– Isotonic: Having the same osmolarity
– Hypotonic: Having an osmolarity less than the surrounding
blood plasma or cells.
– Hypertonic: Having an osmolarity greater than the surrounding
blood plasma or cells.
Hypertonic medium- Isotonic medium- Hypotonic mediumwater exits cell
cell fluid volume water enter cells and
they rupture
const
Low osmolality = good hydration beverage
When dissolved in enough water to make 1.0 liter
of solution, which of the following solutes yields
the solution with the highest osmolarity?
a.
b.
c.
d.
0.10 mole of CaCl2
0.15 mole of NaCl
0.30 mole of glucose
All three of the above solutions have the
same osmolarity.
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