File - Olson Chemistry

SECTION 12.1
Types of Mixtures
Teacher Notes and Answers
SECTION 1 Types of Mixtures
1.solution, colloid, suspension
2.The solute will remain in solution, even after
several days.
3.Examples include metal alloys, oxygen dissolved
in water, and air.
4.water; gelatin
5.nonelectrolyte; electrolyte
Review
1a.Orange juice is a heterogeneous mixture
because the pulp and aqueous components
together constitute a suspension.
1b.Tap water is a homogeneous mixture because
the solutes and water constitute a solution that
is uniform throughout.
2a.Student drawings should show ions dispersed in
a solvent.
2b.Student drawings should show a cubical crystal
lattice with solid bonds that do not allow
movement of particles.
3.Sand in water can settle or be filtered out,
proving that it is not a solution. Dissolved
sugar cannot be removed from the water
through settling or filtration; the water must be
evaporated.
4a.silver, copper; gold
4b.sugar; water
4c.carbon dioxide; water
5.Water, the solvent, is evaporating, leaving behind
the dissolved salts, or solutes, as solids.
Solutions
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SECTION 12.1
Types of Mixtures
The chapter “Matter and Change” discussed the various
types of matter. One type of matter is a mixture. Some
materials are easy to identify as mixtures, because the
different components are visible. For example, soil is a
mixture of rock debris, clay, and decomposed animal and
plant matter.
Key Terms
solution
suspension
colloid
soluble
solvent
solute
electrolyte
nonelectrolyte
Other mixtures are less obvious. Milk is a mixture of
water, fats, proteins, and sugar. Both milk and soil are
heterogeneous mixtures, because their composition is not
uniform. Salt water is a mixture of salt and water, but it has
a uniform composition. Salt water is an example of a
homogeneous mixture.
This section will discuss three types of mixtures. A
solution is a homogeneous mixture of two or more
substances in a single phase. The other two types of
mixtures are heterogeneous: suspension and colloids. A
suspension is a mixture in which the particles are so large
that they settle out unless the mixture is constantly stirred
or agitated. Colloids form when the particle size is in
between those of solutions and suspensions.
Both milk and salt water look like
homogeneous mixtures, but milk is
a heterogeneous mixture called a
colloid.
Properties of Solutions, Colloids, and Suspensions
Solutions
Colloids
Suspensions
Homogeneous
Heterogeneous
Heterogeneous
Particle size:
0.01–1 nm; can
be atoms, ions,
molecules
Particle size:
1–1000 nm,
dispersed; can be
aggregates or
large molecules
Particle size: over
1000 nm, suspended;
can be large particles
or aggregates
Do not separate
on standing
Do not separate
on standing
Particles settle out
Cannot be
separated by
filtration
Cannot be
separated by
filtration
Can be separated by
filtration
Do not scatter
light
Scatter light
(Tyndall effect)
May scatter light, but
are not transparent
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CHAPTER 12
READING CHECK
1. Order the three types of mixtures from those with the smallest
to largest in particle size.
Solutions are homogeneous mixtures.
When a sugar cube is dropped in water, it dissolves. The cube
gradually disappears as sugar molecules leave the surface of
the cube and mix with water molecules. Eventually, all of the
sugar molecules become spread out evenly among the water
molecules. None of the original sugar cube will be visible. If
you taste the sugar water after it is completely dissolved, then
every sip will have the same proportion of sugar and water.
The sugar is soluble, which means that it can dissolve.
Components of Solutions
In a solution, all of the molecules, atoms, or ions are
thoroughly mixed. The solution has the same composition and
properties throughout. The medium that dissolved the other
substance is called the solvent. In the sugar-water example,
water is the solvent. The substance that was dissolved is called
the solute. The sugar is the solute in a sugar water solution. In
general, the component with the smaller amount in the
solution is called the solute.
In a solution, the dissolved particles are so small they
cannot be seen. They also remain mixed with the solvent
indefinitely, as long as the conditions do not change. If a
solution is poured through filter paper, it will remain a
solution. This is because the particles in a solution are less
than a nanometer in diameter.
Water
molecule, H2O
(a)
Ethanol molecule,
C2H5OH
T I P When a solution is close
to a 50%-50% mixture of
two substances, it is difficult and
unnecessary to designate one
substance the solution and the
other substance the solvent.
READING CHECK
2. What will happen to the solute
in a jar of a sugar-water solution if
you leave it in a dark place for
several days without disturbing it?
Copper ion, Cu2+
Water
Chloride
molecule, H2O
ion, Cl-
(b)
(a) An ethanol-water solution has a
liquid solvent and a liquid solute.
(b) A copper(II) chloride–water
solution has a liquid solvent and a
solid solute. Both solutions have a
uniform composition.
Solutions
3
Gold
Gold
(a) 24 karat
(b) 14 karat
Types of Solutions
Most of the examples of solutions that have been discussed so
far have been made up of a solid in a liquid or a liquid in a
liquid. However, there are many other types of solutions.
A liquid can, in fact, dissolve substances in any of the three
main states of matter: solid, liquid, or gas. For example, oxygen
gas dissolves in water. This dissolved oxygen is what oceanic
animals, such as fish, breathe when they pass water through
their gills.
Liquids are not the only substances that can be solutes.
A gas can dissolve another gas. For example, air is a
homogeneous solution of nitrogen, oxygen, and other gases. In
air, nitrogen is the solvent and the other gases are the solutes.
A solid can also be a solvent. An alloy is a solution of two
of more elements that are metallically bonded. The metal that
makes up the greatest percentage of the alloy is the solvent.
The atoms in an alloy are distributed evenly, as shown in the
diagram above.
The mixing of metals in alloys yields desirable properties.
Pure gold (also called 24-karat gold) is too soft to use in
jewelry. Therefore, silver and copper are mixed with the gold
to give it greater strength and hardness while maintaining its
color and resistance to corrosion. Other common alloys
include brass (zinc and copper), sterling silver (silver and
copper), and steel (iron and usually carbon).
READING CHECK
3.
4
Give at least three examples of solutions in which the
solvent is either a gas or a solid.
CHAPTER 12
Silver
Copper
(a) 24-karat gold is pure gold.
(b) 14-karat gold is an alloy of gold
with silver and copper. Gold makes up
14/24 of the alloy.
The particles in a suspension are large.
A jar of muddy water is an example of a suspension. If left
undisturbed, the soil particles collect on the bottom of the jar.
The soil particles are denser than water, and their mass is too
large for intermolecular forces to keep gravity from pulling
them to the bottom. Particles larger than 1000 nm—more than
1000 times larger than atoms—form suspensions. A filter can
also remove particles from a suspension.
Colloids have particles of intermediate size.
Particles that are between 1 nm and 1000 nm in diameter may
form colloids. After large soil particles settle out of muddy
water, the water is often still cloudy because colloidal particles
remain in the water. In this colloid, the water is the dispersing
medium. The colloidal particles are called the dispersed phase.
The motion of the surrounding particles prevents colloidal
particles from settling out, even after long periods of time.
Under a microscope, these particles can appear as rapidly
moving tiny specks of light. The random motion and collisions
of these particles is called Brownian motion.
Tyndall Effect
Many colloids, such as milk, appear homogeneous because the
individual particles cannot be seen. However, the particles are
large enough to scatter light. The Tyndall effect is the
scattering of light by colloidal particles in a transparent
medium. This effect is responsible for a headlight beam being
visible from the side on a foggy night. The Tyndall effect can
be used to distinguish a colloid from a solution.
The particles in a colloid will scatter a
beam of light, while the particles in a
solution will not. The left-hand jar
holds salt water, a true solution. The
right-hand jar holds a colloid of
gelatin and water.
READING CHECK
4. In the gelatin-water colloid
above,
is the dispersing medium and
is the dispersed phase.
Classes of Colloids
Class of colloid
Phases
Example
Sol
solid dispersed in liquid
paints, mud
Gel
solid network throughout liquid
gelatin
Liquid emulsion
liquid dispersed in a liquid
milk, mayonnaise
Foam
gas dispersed in liquid
shaving cream, whipped cream
Solid aerosol
solid dispersed in gas
smoke, auto exhaust
Liquid aerosol
liquid dispersed in gas
fog, mist, clouds, aerosol spray
Solid emulsion
liquid dispersed in solid
cheese, butter
Solutions
5
Electrolytes are ionic solutions that conduct electricity.
Substances that dissolve in water are classified by the nature
of the particles in solution. If the substance dissolves in water
to form a solution that can conduct electric current, then the
substance is called an electrolyte.
Any soluble ionic compound will separate into its positive
and negative ions when it dissolves in water. For example,
sodium chloride is an electrolyte that separates into an
N​a+
​ ​cation and a C​l–​ ​anion in water. Another example
of an ­electrolyte is a highly polar molecular compound.
Hydrogen chloride, HCl, forms the ions H
​ 3​ ​​O​+​and C​l–​ ​when
dissolved in water.
CONNECT
For electric current to flow, a
complete circuit must be formed. A
complete circuit includes a power
source, usually a battery. The
current must be able to flow
uninterrupted from the positive
terminal of the battery to the
negative terminal of the battery.
If the substance dissolves in water to form a solution that
cannot conduct electric current, then the substance is called a
nonelectrolyte. These substances form neutral solute particles,
usually molecules. Sugar is an example of a nonelectrolyte.
One way to test the electrical conductivity of a solution
is shown below. Two electrodes are connected to a power
supply and a light bulb and lowered into water without
touching. For an electric current to flow, the solution
must be able to conduct charge from one electrode to
the other. If the light bulb does not light up, the solution
contains nonelectrolytes.
Chloride ion,
Cl−
Water molecule,
H2O
Sugar molecule,
C12H22O11
Water molecule,
H2O
Sodium
ion,Na+
(a) Salt solution—
electrolyte solute
(b) Sugar solution—
nonelectrolyte solute
Of the three dissolved substances above, (a) sodium chloride is an electrolyte,
(b) sucrose is a nonelectrolyte, and (c) hydrogen chloride is an electrolyte.
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CHAPTER 12
READING CHECK
5. A substance that dissolves in
water and forms molecules in
solution is called a(n)
.
A substance that dissolves in water
and forms ions in solution is called
a(n)
Hydronium ion,
H3O+
.
Water molecule,
H2O
Chloride
ion, Cl-
(c) Hydrochloric acid solution—
electrolyte solute
SECTION 12.1 REVIEW
VOCABULARY
1. Classify the following as either a heterogeneous or homogeneous mixture,
and explain your answers.
a. orange juice
b. tap water
REVIEW
2. a. Make a drawing of the particles b. Make a drawing of the particles in
in an NaCl solution to show why an NaCl crystal to show why pure
this solution conducts electricity.
salt does not conduct electricity.
3. Describe one way to prove that a mixture of sugar and water is a solution
and that a mixture of sand and water is not a solution.
4. Name the solute and solvent in the following solutions.
a. 14-karat gold
Solute:
Solvent:
b. corn syrup
Solute:
Solvent:
c. carbonated water
Solute:
Solvent:
Critical Thinking
5. ANALYZING INFORMATION If a jar of sea water sits in the sun, the liquid level
steadily decreases, and finally crystals appear. What is happening?
Solutions
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