Chapter 20 PPT

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Heterogeneous
Mixtures
matter
pure
substances
mixtures
matter
pure
elements
substances
compounds
mixtures
iron
gold
lead
uranium
sodium chloride
glucose
calcium carbonate
water
matter
pure
substances
elements
compounds
iron
gold
lead
uranium
sodium chloride
glucose
calcium carbonate
water
mixtures
homogeneous
mixtures
heterogeneous
mixtures
mixtures
air
gasoline
14 karat gold
seawater
granite
soil
blood
chocolate cake
matter
pure
substances
elements
iron
gold
lead
uranium
compounds
mixtures
homogeneous
mixtures
sodium chloride
air
glucose
gasoline
calcium carbonate 14 karat gold
water
seawater
heterogeneous
mixtures
granite
soil
blood
chocolate cake
Mixtures
• All matter is either a pure
substance or a mixture.
• Most of the “stuff” in this world
is in the form of a mixture.
Properties of Mixtures
1. Particles are physically
combined, not chemically
combined; so they can be
separated by physical means.
2. A mixture can be made in any
proportion.
3. The parts of a mixture keep
their own properties.
Six Phases of Mixtures
1.
2.
3.
4.
5.
6.
Gel
Sol
Emulsion
Foam
Aerosol
Heterogeneous Alloy
Classifying Mixtures
by Phase
• A homogeneous mixture has
one phase.
 Another word for this is
solution.
Classifying Mixtures
by Phase
• A heterogeneous mixture has
distinct phases.
 If only the word mixture is
used, it is understood to be
heterogeneous.
What is a solution?
1.
2.
3.
4.
Homogeneous mixture
Heterogeneous mixture
Compound
Pure Substance
Question
Classifying Mixtures
by Phase
• Continuous phase—an
unbroken phase in which the
other phases are mixed
 Ex: the sand in a sand-androcks mixture
Classifying Mixtures
by Phase
• Dispersed phase—scattered
throughout the continuous
phase
 Ex: the rocks in a sand-androcks mixture
Classification by Phase
• Gel—a solid dispersed in a
liquid that has some rigidity
 Ex: dessert gelatin
Classification by Phase
• Sol—a solid-in-liquid mixture
that is more “liquidy”
 Ex: paints and inks
Classification by Phase
• Emulsions—contain two or more
phases in the liquid state
 The liquids will not mix
(immiscible).
 Sometimes a liquid is made
of such small particles that
it is not visible as a separate
substance.
Classification by Phase
 Over time the liquids will
separate.
 Homogenization, a
thorough mixing process,
can slow the separation.
 Ex: cream cheese, milk,
mayonnaise, and butter
Classification by Phase
• Foam—gas dispersed in a
liquid
 Ex: whipped cream,
shaving foams
• Aerosols—solid or liquid
dispersed in a gas
 Ex: dust in air, water in air
Classification by Phase
• Heterogeneous alloys—solidsolid mixture; usually metal
 Ex: fuel plate in nuclear
reactors
Ink is an example of a(n) ______.
1.
2.
3.
4.
gel
sol
emulsion
dispersed phase
Question
Classifying Mixtures
by Particle Size
1. Colloidal Dispersion
2. Suspension
Colloidal Dispersions
• Colloidal dispersions consist of
particles too small to see.
• Therefore the dispersion can
look like a homogeneous
mixture.
• The dispersed particles are
called colloids.
Colloidal Dispersions
• The colloidal particles are too
small to settle out.
• The thermal vibrations of the
continuous phase particles keep
the dispersed phase mixed.
• Many gels, sols, emulsions,
foams, and aerosols are colloidal
dispersions.
Suspensions
• Suspension particles are larger
than colloids and will eventually
settle out.
Solutions
• Solutions have the tiniest
particles.
Classifying Mixtures
by Particle Size
• The particles in a colloidal
dispersion or suspension are
large enough to scatter light.
 This scattering is called the
Tyndall effect.
• The particles dissolved in a
solution are too small and do not
scatter the light.
suspensions/
dispersions
solutions
Which of the following contains
particles that settle out?
1.
2.
3.
4.
solution
colloidal dispersion
suspension
homogeneous mixture
Question
Homogeneous
Mixtures
Homogeneous Mixtures
• Homogeneous mixtures
(solutions) are uniform mixtures
with a single phase, but two
substances are involved.
• The solute is the substance
being dissolved.
• The solvent is the substance
doing the dissolving.
Homogeneous Mixtures
• There is always less solute than
solvent in the mixture.
• Although the solute is
completely mixed in the solvent,
there is no chemical
combination.
• No new substance is formed.
Types of Solutions by Solvent
• Liquid solutions
 most common
 solute: solids, liquids, and/or
gases
 Ex: salt + water, sugar +
water, carbon dioxide +
water
Types of Solutions by Solvent
• Solid solutions
 solute: solids, liquids, and/or
gases
• gas-in-solid: H2 into platinum
• liquid-in-solid: mercury into
gold (called an amalgam)
• solid-in-solid: alloys (metals
mixed in a liquid state and
then cooled)
Types of Solutions by Solvent
• Gas solutions
 solute: only gases
 Ex: air (nitrogen + oxygen)
Water
• Water is the most common
solvent in liquid solutions.
• It is such a good solvent
that it is nearly impossible
to find 100% pure water.
Water
• Its structure (bent) makes it
an effective solvent.
• Since water is polar, it
attracts ionic and polar
covalent substances.
The Solution Process
• For an ionic solid such as salt
to dissolve, the bonds
between the sodium and
chloride ions must be broken.
• This process generally is
called dissociation.
• The specific term for
dissociation of polar covalent
or ionic solids is ionization.
The Solution Process
• Then other water molecules
attach to the separated ions in
a process called hydration.
• If the solvent is not water, the
second process is called
solvation.
The Solubility Rule
Like dissolves like.
This means that polar solvents
dissolve polar and ionic
solutes, and nonpolar solvents
dissolve nonpolar solutes.
“Like dissolves like” means:
1.
2.
3.
4.
what you like dissolves
polar dissolves polar
polar dissolves nonpolar
a substance eats
whatever it likes
Question
Solubility
• A few liquid solutes are
infinitely soluble in some
liquid solvents.
• This means that they can
freely mix in any proportion.
• The term for this property is
miscible.
Solubility
• Ex: alcohol and water
Solubility
• The opposite of miscible is
immiscible.
• Liquid solutes that cannot mix
with liquid solvents are
immiscible.
Solubility
• Most solvents have a limit as
to how much solute they can
dissolve.
• That limit is called solubility.
• Solubility is stated in grams of
solute that can be dissolved
into 100 mL of water.
Factors Affecting Solubility
• There are two factors that
affect solubility:
1. Temperature
2. Pressure
Solubility and Temperature
• When dissolving liquids or
solids, an increase in
temperature equals an
increase in solubility.
• When dissolving gases, an
increase in temperature
equals a decrease in
solubility.
Solubility and Pressure
• When dissolving liquids or
solids, pressure has no
noticeable effect on
solubility.
• When dissolving gases, an
increase in pressure equals
an increase in solubility.
Henry’s Law
Solubility of gases
increases with the partial
pressure of the gas above
the solution.
Saturation
• When a solute is at the
solubility limit, the solution is
said to be saturated.
• If less than the maximum
amount of solute is dissolved,
the solution is unsaturated.
Saturation
• If a saturated solution is cooled,
it can become supersaturated.
• Supersaturated means it has
more than the usual maximum
amount of solute dissolved.
• If the supersaturated solution is
disturbed, the excess solute will
quickly fall out of the solution
(precipitate).
When the solubility limit is
exceeded, a ______ results.
1.
2.
3.
4.
solution
precipitate
solvent
solute
Question
If you are trying to dissolve a
solid into a liquid and increase
the temperature, the solid will
1. not dissolve.
2. fully dissolve.
3. dissolve less.
4. dissolve more.
Question
If you are trying to dissolve a
gas into a liquid and increase
the temperature, the gas will
1. not dissolve.
2. fully dissolve.
3. dissolve less.
4. dissolve more.
Question
The harder you push a gas into
solution,
1.
2.
3.
4.
the more it will dissolve.
the less it will dissolve.
the hotter it will become.
the colder it will become.
Question
Rate of Solution
• The rate of solution is affected
by two factors:
1. inherent solubility
2. the number of effective
solute-solvent collisions
Number of Collisions
• The number of collisions can be
changed by:
• changing the
temperature
• stirring
• changing
the surface
area
Solution
Concentration
Concentration
• Concentration is the amount of
solute that is dissolved.
• Dilute and concentrated are too
vague.
Percentage by Mass
g solute
× 100
g solution
This is comparing different
concentrations of the same
solution.
Sample Problem
If 5.81 g of salt is dissolved in
water to make 56.3 g of solution,
what is the percent by mass?
5.81 g solute
× 100 = 10.3%
56.3 g solution
If 10 g of sugar is added to 90 g
of water, what is the percent by
mass?
1.
2.
3.
4.
10%
11%
5%
20%
10 g sugar
= 10%
100 g total
Question
When 25 g of salt is dissolved to
make a 125 g solution, what is
the percent by mass?
1.
2.
3.
4.
10%
25 g salt
20%
= 20%
16.7% 125 g total
25%
Question
Molarity
• Molarity is a measure of the
number of solute particles
dissolved rather than the mass
of dissolved particles.
• Since the size of the particles
is so small, the number is
tremendously large.
Molarity
• The unit used to measure the
number of particles is the mole.
• A mole of solute has
6.022 × 1023 particles.
moles of solute
molarity =
L of solution
Colligative Properties
Colligative properties
depend only on the number
of solute particles dissolved
in the solution.
Colligative Properties
• Colligative properties affect
 boiling point
 freezing point
 osmotic pressure
Boiling Point
• An increase in solute raises
the boiling point.
• Solute interferes with boiling,
so the temperature must be
increased in order to reach the
boiling point.
Freezing Point
• An increase in solute lowers
the freezing point.
• Solute interferes with freezing,
so the temperature must be
lowered in order to reach the
freezing point.
Osmosis
• Osmosis is the movement of
solvent (often water) from a
high concentration to a low
concentration through a semipermeable membrane.
• Water moves from a region of
high concentration to a region
of low concentration of water.
Osmosis
• Osmosis can also be described
as water going from a diluted
solution to a concentrated
solution.
Semi-permeable membrane
Water
Sugar
Water
Osmotic Pressure
Osmotic pressure is the
amount of pressure
required to stop osmosis.
Reverse Osmosis
• Reverse osmosis also requires
a semi-permeable membrane,
which can be used to separate
seawater from freshwater in
order to make it drinkable.
• The process of removing salt
from seawater is called
desalination.
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