Chapter 13
Pages 395 - 418
Types of Mixtures
 Solutions
 Suspensions
 Colloids
Solutions
Solution: a homogeneous mixture of 2 or more
substances in a single phase
-atoms, molecules, or ions are
thoroughly mixed, resulting in a
mixture that has the same composition
and properties throughout
Soluble: capable of
being dissolved
Particle Model for a Solution
Components of Solutions
Solvent – the dissolving medium in a
solution
Solute – the substance dissolved in a
solution (usually the component that
is lesser quantity)
Types of Solutions
-exist as gases, liquids, or solids
Alloy – solutions of solids
uniformly mixed (brass, sterling
silver)
Particle Models for Gold and Gold
Alloy
Properties of Solutions
•Particle size: 0.01 – 1 nm; can be atoms, ions,
molecules
•Do not separate on standing
•Cannot be separated by filtration
•Do not scatter light
•Homogeneous
Suspensions
Suspension: a mixture in which the
particles of a solvent are so large that they
settle out unless the mixture is constantly
stirred or agitated
Examples: muddy water,
Italian salad dressing
Particle Model for a Suspension
Properties of Suspensions
•Particle size: over 1000 nm, suspended; can
be large particles or aggregates
•Particles settle out
•Can be separated by filtration
•May scatter light, but are not transparent
•heterogeneous
Colloids
Colloids: particles that are intermediate in
size between those in solutions and
suspensions form mixtures known as colloidal
dispersions
-particles are small and suspended
by constant movement
-dispersed phase: colloidal particles
-dispersing medium: water
Examples: emulsions (mayonnaise), foam
(shaving cream), gelatin, aerosols
Tyndall Effect
-occurs when light is scattered by colloidal
particles dispersed in a transparent medium.
This property can be used to distinguish
between a solution and a colloid.
Properties of Colloids
•Particle size: 1-1000 n, dispersed; can be
aggregates or large molecules
•Do not separate on standing
•Cannot be separated by filtration
•Scatter light (Tyndall effect)
•heterogeneous
Solutes: Electrolytes vs.
Nonelectrolytes
•Substances that dissolve
in water are classified
according to whether
they yield molecules or
ions in solution.
•Ionic compounds
dissolve to yield + and
– ions surrounded by
water molecules.
•Ions are free to move and
therefore conduct
electricity.
Particle Models for
Electrolytes/Nonelectrolytes in Solution
Definitions
Electrolyte: a
substance that
dissolves in water to
give a solution that
conducts electric
current
Examples:
NaCl, HCl
(highly polar)
Nonelectrolyte: a
substance that
dissolves in water
to give a solution
that does not
conduct an electric
current
Example:
sugar
solution
Factors Affecting the Rate of
Dissolution
•Increasing the surface area of the
solute
•Agitating the solution
•Heating the solvent
Increasing the Surface Area
To dissolve:
•Molecules or ions of the solute are attracted
by the solvent
•Dissolution occurs at the surface of the
solute
•Increasing surface area of solute speeds up
the process
•The more finely divided a substance is, the
greater the surface area per unit mass and
the more quickly it dissolves
Agitating a Solution
•Concentration of dissolved solute is high
near surface of a solute
•Stirring or shaking disperses solute
particles and brings fresh solvent in contact
with the solute surface
•Stirring is similar to crushing a solid –
contact between solvent and solute surface is
increased
Heating a Solvent
•With increase in solvent temperature,
solvent molecules move faster and KE
increases
•At higher temperatures, collisions
between solvent and solute molecules are
more frequent and of higher energy
•This separates solute molecules from one
another and disperses them among the
solvent molecules
Solubility
Saturated
Unsaturated
Supersaturated
Solubility
-for every
combination of
solvent and solid
solute at a given
temperature, there is
a limit to the amount
of solute that can be
dissolved
-the point at which
this limit is reached
depends on the
nature of the solute,
the nature of the
solvent, and the
temperature
Model
-sugar dropped in water
-sugar molecules leave
solid and move at
random in solvent
-some may collide with
solid and remain there
-as more solid dissolves,
collisions increase
-eventually, molecules
are returning to the
crystal at the same rate
at which they are going
into solution
Solution equilibrium: the physical state in which
the opposing processes of dissolution and
crystallization of a solute occur at equal rates
Saturated
Saturated solution: a solution that contains
the maximum amount of dissolved solute
How to tell a solution is saturated –
when more solute is added it falls to the
bottom and does not dissolve
Unsaturated
Unsaturated solution: a solution
that contains less solute than a
saturated solution under the
existing conditions
Supersaturated
-if solubility increases w/temperature, the
excess solute usually comes out of solution,
leaving the solution saturated at the lower
temp
-sometimes, if the solution cools undisturbed,
the excess solute does not separate
Supersaturated solution: a solution that
contains more dissolved solute than a saturated
solution contains under the same conditions
-dropping a small crystal of the solute into a
supersaturated solution (seeding) or disturbing
the solution causes a rapid formation of crystals by
the excess solute
-once crystals begin to form, the process
continues until equilibrium is established at the
lower temp
Solubility: of a substance is the amount of that
substance required to form a saturated solution
with a specific amount of solvent at a specified
temperature
-temperature must be specified because
solubility varies with temperature (for gases,
pressure must also be specified)
-the maximum amount of solute that dissolves
and reaches equilibrium is always the same
under the same conditions
Solute-Solvent Interactions
Rule of Thumb: “like
dissolves like”
-substances are alike
when similar in type of
bonding, the polarity or
nonpolarity of molecules,
and the intermolecular
forces between solute
and solvent
Dissolving Ionic Compounds in
Aqueous Solution
-polarity of water plays important role
-charged ends attract ions in ionic compounds
and surround them to keep them separated from
other ions in the solution
-attraction is strong enough to draw ions away
from crystal surface and into solution
Hydrated: the solution process with water as
the solvent
-ions are said to be “hydrated”
-entire crystal dissolves and hydrated ions are
uniformly distributed
-as crystals reform they retain specific ratios of
water molecules and are known as hydrates
(CuSO4 . 5H2O)
-a hydrate’s behavior is just like that of the
anhydrous form; dissolving results in hydrated
ions and water
-ions and polar molecules are linked to water
with dipole-dipole attractions
Nonpolar Solvents
-generally, ionic
compounds are not soluble
in nonpolar solvents
-nonpolar solvent molecules
do not attract ions strongly
enough to overcome the
forces holding the crystal
together
-nonpolar molecules are
linked to nonpolar solvents
with London dispersion
forces
Examples:
CCl4
C6H5CH3
(toluene)
gasoline
Liquid Solutes and
Solvents
Immiscible: liquid
solutes and solvents
that are not soluble in
each other
Examples: nonpolar
with polar, toluene
with water, gasoline
with water, oil and
water
Miscible: liquids that
dissolve freely in one
another in any
proportion
-the nonpolar molecules of
these substances exert no
strong forces of attraction
or repulsion, and the
molecules mix freely
Examples: nonpolar
w/nonpolar, gas with
fats, oils, and greases
Effects of Pressure on Solubility
-pressure changes have very little effect on the
solubilities of liquids
-increases in pressure increase gas solubilities
in liquids
-equilibrium eventually reached between rates at
which gas molecules enter and leave the gas
phase
gas + solvent
solution
-increasing the pressure of the solute gas above
the solution puts stress on the equilibrium
-an increase in gas pressure causes the
equilibrium to shift so that fewer molecules are
in the gas phase
Example: gas escapes immediately when
pressure is reduced by opening a soda bottle.
The soda effervesces when the bottle is opened
and the pressure is reduced.
Henry’s
Law
Henry’s Law: the solubility of a gas in a liquid is
directly proportional to the partial pressure of
that gas on the surface of the liquid
-named after English chemist,
William Henry
-in a mixture of gases, each gas exerts a pressure.
Assuming they don’t react, each gas will dissolve
to the same extent it would if no other gases
were present.
Application of Henry’s Law
In sodas, the
solubility of CO2 is
increased by increasing
the pressure. It’s raised to
5-10 atm. When the cap is
removed, the pressure is
reduced to 1 atm and some
of the CO2 escapes.
Effervescence – the rapid escape of
a gas from a liquid in which it is
dissolved
Effects of Temperature on
Solubility
On Gases
-increasing temperature
usually decreases gas
solubility
-increase in temperature;
increase in KE
-therefore, more molecules
overcome attraction and
return to gas phase
-at higher temps,
equilibrium is reached with
fewer gas molecules in
solution
On Solids
-more difficult to predict
-often, increase in temp
increases solubility of solids
-sometimes the increase in
solubility is large and
sometimes only slight (see
solubility table )
-in some cases, solubility
decreases with an increase
in temp
Temperature – Solubility
Heats of Solution
-formation of a solution means an energy change
-dissolving some solids results in heat formation –
exothermic (hot)
-dissolving others results in the absorption of
heat – endothermic (cold)
-both solvent and solute must undergo changes in
the forces holding them together
-energy is required to separate solute molecules
and solvent molecules
-solvated: a solute particle that is surrounded by
solvent molecules
Heat of Solution: net amount of heat energy
absorbed or released when a specific amount of
solute dissolves in a solvent
-since heating decreases solubility of a gas,
dissolution of gases is exothermic (negative values)
Energy Changes in the Solution
Process