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CHEMISTRY
The Central Science
8th Edition
Chapter 13
Properties of Solutions
P. Hatch
The Solution Process
• Solution: a homogeneous mixture of solute (present in
smallest amount) and solvent (present in largest amount).
• Solute and solvent are components of the solution.
• In the process of making solutions with condensed
phases, intermolecular forces become rearranged.
Types of Solutions
The Solution Process
• Consider NaCl (solute) dissolving in water (solvent):
–
–
–
–
–
the water H-bonds have to be interrupted,
NaCl dissociates into Na+ and Cl-,
ion-dipole forces form: Na+ … -OH2 and Cl- … +H2O.
We say the ions are solvated by water.
If water is the solvent, we say the ions are hydrated.
The Solution Process
Ion-dipole
Saturated Solutions and
Solubility
• Dissolve: solute + solvent  solution.
• Crystallization: solution  solute + solvent.
• Solubility: maximum amt. of solute dissolved in a given
amt. of solvent; amount of solute required to form a
saturated solution.
• Saturation: maximum amt. of solute dissolved;
crystallization and dissolution are in equilibrium.
• Supersaturated: a solution formed when more solute is
dissolved than in a saturated solution.
Solution Composition
• Qualitative composition: sol’ns are dilute or concentrated
• Quantitative composition: amount of solute per amount of
solvent (or sol’n).
Mass Percent: percent by mass of solute in a sol’n
Mole Fraction (X): ratio of moles of given component
to total moles in sol’n
Molarity (M): moles of solute per L sol’n
Molality (m): moles of solute per kg solvent
Ways of Expressing
Concentration
mass of component in solution
mass % of component 
100
total mass of solution
moles of component in solution
Mole fraction of component 
total moles of solution
moles solute
Molarity 
liters of solution
moles solute
Molality, m 
kg of solvent
Converting between molarity (M) and molality (m)
requires density.
Solution Composition
A solution is prepared by mixing 30.0 mL of butane (C4H4,
d = 0.600 g/mL) with 65.0 mL of octane (C8H18, d = 0.700
g/mL). Assuming that the volumes are additive, calculate
the following for butane:
a.
b.
c.
d.
Molarity
Mass percent
Mole fraction
Molality
Factors Affecting
Solubility
Structural effects
• Number of carbon atoms in a chain
• Number of –OH groups in a molecule
• Type of solid
Pressure effects
Temperature effects
The Solution Process
Energy Changes and Solution
Formation
• Step 1: separate solute into individual particles
Endothermic, DH > 0
• Step 2: separate solvent’s intermolecular forces
Endothermic, DH > 0
• Step 3: solvent-solute interact to form intermolecular
forces
Mostly Exothermic, DH < 0
When not exothermic, solution forms due to
increase in entropy, DS > 0
The Solution Process
Energy Changes and Solution
Formation
• Rule: “like dissolves like”
• solubility is favored if solute and solvent have similar
properties
• polar solvents dissolve polar solutes.
• non-polar solvents dissolve non-polar solutes.
• Why?
Factors Affecting
Solubility
Solute-Solvent Interaction
• Miscible liquids: mix in any proportions.
• Immiscible liquids: do not mix.
• The number of carbon atoms in a chain affect solubility:
the more C atoms the less soluble in water.
• The number of -OH groups within a molecule increases
solubility in water.
Factors Affecting
Solubility
Solute-Solvent Interaction
Factors Affecting
Solubility
Solute-Solvent Interaction
Factors Affecting
Solubility
Solute-Solvent Interaction
Discuss the solubility of each of the following solutes in
carbon tetrachloride:
a. Ammonium nitrate
b. 1-pentanol (CH3CH2CH2CH2CH2OH)
c. Pentane (CH3CH2CH2CH2CH3)
Factors Affecting
Solubility
Solute-Solvent Interaction
• Covalent-network solids, like sand and diamond, do
not dissolve!
• Why not?
Factors Affecting
Solubility
Pressure Effects
•Solubility of a gas in a
liquid is a function of
the pressure of the gas.
•Higher the P, the greater
the solubility.
•Lower the P, the lower
the solubility.
•WHY?
Factors Affecting
Solubility
Pressure Effects
• Carbonated beverages are bottled with a partial pressure
of CO2 > 1 atm.
• As the bottle is opened, the partial pressure of CO2
decreases and the solubility of CO2 decreases.
• Therefore, bubbles of CO2 escape from solution.
Factors Affecting
Solubility
Temperature Effects
• Experience tells us that sugar dissolves better in warm
water than cold.
• As temperature increases, solubility of solids generally
increases.
• Sometimes, solubility decreases as temperature increases
(e.g. Ce2(SO4)3).
Factors Affecting
Solubility
Temperature Effects
• Experience tells us that carbonated beverages go flat as
they get warm.
• Therefore, gases get less soluble as temperature
increases.
• Thermal pollution: if ponds and lakes get too warm,
CO2 and O2 become less soluble and are not available for
aquatic plants or animals.
Colligative Properties
• Colligative properties: physical properties of a sol’n that
depend on the number of solute particles but NOT the
identity of those particles.
Vapor pressure lowering
Boiling point elevation
Freezing point depression
Osmotic pressure
Colligative Properties
Lowering Vapor Pressure
• Non-volatile solutes reduce the ability of the surface
solvent molecules to escape the liquid.
• Therefore, vapor pressure is lowered.
• The amount of vapor pressure lowering depends on the
amount of solute.
• The more solute particles present, the greater the
vapor pressure lowering.
Colligative Properties
Lowering Vapor Pressure
Raoult’s Law: the vapor pressure of a sol’n (PA) is directly
proportional to the mole fraction of the solvent (XA)
present.
PA   A P A
• PA = vapor pressure of sol’n
• PA = vapor pressure of pure solvent
• A = the mole fraction of solvent.
Colligative Properties
Lowering Vapor Pressure
The vapor pressure of a sol’n containing 53.6 g of glycerin,
C3H8O3, in 133.7 g of ethanol, CH3CH2OH, is 113 torr at
40oC. Calculate the vapor pressure of the pure ethanol at
40oC assuming that glycerin is a nonvolatile solute in
ethanol.
PA   A P A
Colligative Properties
Lowering Vapor Pressure
• Ideal solution: one that obeys Raoult’s law.
• Raoult’s law breaks down when the solvent-solvent and
solute-solute intermolecular forces are greater than
solute-solvent intermolecular forces.
Colligative Properties
Boiling-Point Elevation
• A non-volatile solute increases the boiling point of a
solvent.
• At 1 atm (normal boiling point of pure liquid) there is a lower
vapor pressure of the solution. Therefore, a higher
temperature is required to reach a vapor pressure of 1 atm for
the solution (DTb).
• Molal boiling-point-elevation constant, Kb, expresses
how much DTb changes with molality, m:
DTb  Kb m
Colligative Properties
Freezing Point Depression
• A non-volatile solute decreases the freezing point of a
solvent.
• Decrease in freezing point (DTf) is directly proportional
to molality (Kf is the molal freezing-point-depression
constant):
DT f  K f m
Colligative Properties
Colligative Properties
How does the presence of a non-volatile solute affect the
phase diagram for a solvent?
a.
b.
c.
d.
Vapor pressure curve is lowered
Melting curve is lowered
Boiling Point is increased (Temp of VP curve at 1 atm)
Melting Point is decreased (Temp of MP curve at 1 atm)
Colligative Properties
Osmosis
• Osmosis: the flow of a pure solvent into a sol’n through
a semipermeable memebrane.
• Semipermeable membrane: permits passage of some
components of a solution. Example: cell membranes and
cellophane.
• There is movement in both directions across a
semipermeable membrane.
Colligative Properties
Osmosis
• As solvent moves across the membrane, the fluid levels in
the arms becomes
uneven.
Eventually the
pressure difference
between the arms
stops osmosis.
Colligative Properties
Osmosis
Osmotic pressure, : the pressure required to stop osmosis:
V  nRT
n

    RT
V 
 MRT
•
•
•
•
 = osmotic pressure in atm
M = molarity of sol’n, mol/L
R = gas law constant, 0.0821 L.atm/mol.K
T = temperature in Kelvin
Colligative Properties
Osmosis
• An aqueous solution of 10.00 g of catalase, an enzyme
found in liver, has a volume of 1.00 L at 27oC. The
solution’s osmotic pressure at 27oC is 0.745 torr.
Calculate the molar mass of the catalase.
 = MRT; M = molarity
Colligative Properties
•
•
•
•
Osmosis
Isotonic solutions: two solutions with the same 
separated by a semipermeable membrane.
Hypotonic solutions: a solution of lower  than a
hypertonic solution.
Osmosis is spontaneous.
Red blood cells are surrounded by semipermeable
membranes.
Colligative Properties
Osmosis
• Crenation:
– red blood cells placed in hypertonic solution (relative to
intracellular solution);
– there is a lower solute concentration in the cell than the
surrounding tissue;
– osmosis occurs and water passes through the membrane out of
the cell.
– The cell shrivels up.
Colligative Properties
Osmosis
Colligative Properties
Osmosis
• Hemolysis:
–
–
–
–
red blood cells placed in a hypotonic solution;
there is a higher solute concentration in the cell;
osmosis occurs and water moves into the cell.
The cell bursts.
• To prevent crenation or hemolysis, IV (intravenous)
solutions must be isotonic.
Colligative Properties
Osmosis
– Cucumber placed in NaCl solution loses water to shrivel up and
become a pickle.
– Limp carrot placed in water becomes firm because water enters
via osmosis.
– Salty food causes retention of water and swelling of tissues
(edema).
– Water moves into plants through osmosis.
– Salt added to meat or sugar to fruit prevents bacterial infection
(a bacterium placed on the salt will lose water through osmosis
and die).
Colligative Properties
Osmosis
• Active transport is the movement of nutrients and waste
material through a biological system.
• Active transport is not spontaneous.
Colloids
• Colloids are suspensions in which the suspended particles
are larger than molecules but too small to drop out of the
suspension due to gravity.
• Particle size: 10 to 2000 Å.
• There are several types of colloid:
–
–
–
–
aerosol (gas + liquid or solid, e.g. fog and smoke),
foam (liquid + gas, e.g. whipped cream),
emulsion (liquid + liquid, e.g. milk),
sol (liquid + solid, e.g. paint),
Colloids
– solid foam (solid + gas, e.g. marshmallow),
– solid emulsion (solid + liquid, e.g. butter),
– solid sol (solid + solid, e.g. ruby glass).
• Tyndall effect: ability of a Colloid to scatter light. The
beam of light can be seen through the colloid.
Colloids
End of Chapter 13
Properties of Solutions