Chapter 7
Section 1 Solutions and
Other Mixtures
Objectives
• Distinguish between heterogeneous mixtures and
homogeneous mixtures.
• Compare the properties of suspensions, colloids,
and solutions.
• Give examples of solutions that contain solids
or gases.
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Chapter 7
Section 1 Solutions and
Other Mixtures
Heterogeneous Mixtures
• The amount of each substance in different samples
of a heterogeneous mixture varies.
• Example: Any two shovelfuls of dirt from a garden
would not be exactly the same.
• A suspension is a mixture in which large particles of
a material are more or less evenly dispersed
throughout a liquid or gas.
• Example: natural orange juice, which contains
particles of pulp.
• Particles in a suspension may settle over time, and
may be filtered out.
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Chapter 7
Section 1 Solutions and
Other Mixtures
Suspension
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Chapter 7
Section 1 Solutions and
Other Mixtures
Heterogeneous Mixtures, continued
• Some combinations of liquids will not mix, but will
separate spontaneously.
• Example: Oil and vinegar in salad dressing
separates into two layers.
• Liquids that do not mix with each other are
immiscible.
• One way to separate two immiscible liquids is to
carefully pour the less dense liquid off the top. This
is called decanting.
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Chapter 7
Section 1 Solutions and
Other Mixtures
Heterogeneous Mixtures, continued
• A colloid is a mixture consisting of tiny particles that
are intermediate in size between those in solutions
and those in suspensions and that are suspended in
a liquid, solid or gas.
• Particles in a colloid are too small to settle out.
• However, particles in a colloid are large enough to
scatter light that passes through: this is called the
Tyndall effect.
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Chapter 7
Section 1 Solutions and
Other Mixtures
Heterogeneous Mixtures, continued
• Examples of familiar materials that are colloids
include gelatin desserts, egg whites, and blood
plasma.
• Some immiscible liquids can form colloids.
• An emulsion is any mixture of two or more
immiscible liquids in which one liquid is dispersed
in the other.
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Chapter 7
Section 1 Solutions and
Other Mixtures
Emulsions
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Chapter 7
Section 1 Solutions and
Other Mixtures
Homogeneous Mixtures
• Homogeneous mixtures not only look uniform, but
are uniform.
• Example: salt water, which looks uniform even when you
examine it under a microscope
• A solution is a homogeneous mixture of two or
more substances uniformly dispersed throughout
a single phase.
• In a solution, the solute is the substance that dissolves in
the solvent.
• The solvent is the substance in which the solute
dissolves.
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Chapter 7
Section 1 Solutions and
Other Mixtures
Homogeneous Mixture
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Chapter 7
Section 1 Solutions and
Other Mixtures
Solutions
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Chapter 7
Section 1 Solutions and
Other Mixtures
Homogeneous Mixtures, continued
• Miscible liquids mix to form solutions.
• One way to separate miscible liquids is by distillation,
which works when the two miscible liquids have
different boiling points.
• Water is a common solvent, but some liquid solutions
contain no water.
• Example: Fuels such as gasoline, diesel fuel, and
kerosene are made from a liquid solution called
petroleum, also called crude oil.
• Components of crude oil are separated by
fractional distillation.
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Chapter 7
Section 1 Solutions and
Other Mixtures
Homogeneous Mixtures, continued
• Other states of matter can also form solutions.
• The air you breathe is a solution of nitrogen,
oxygen, argon, and other gases.
• The liquid element mercury dissolves in solid silver
to form a solution called an amalgam, which can
be used to fill cavities in teeth.
• An alloy is a solid or liquid mixture of two or
more metals.
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Chapter 7
Section 2 How Substances
Dissolve
Objectives
• Explain how the polarity of water enables it to
dissolve many different substances.
• Relate the ability of a solvent to dissolve a solute to
the relative strengths of forces between molecules.
• Describe three ways to increase the rate at which a
solute dissolves in a solvent.
• Explain how a solute affects the freezing point and
boiling point of a solution.
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Chapter 7
Section 2 How Substances
Dissolve
Water: A Common Solvent
• Many different substances can dissolve in water.
For this reason, water is sometimes called the
universal solvent.
• Water can dissolve ionic compounds because of its
structure: it is a polar compound, which is a
molecule that has an uneven distribution of electrons.
• Because they are polar, water molecules
attract both the positive and negative ions of
an ionic compound.
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Chapter 7
Section 2 How Substances
Dissolve
Water: A Common Solvent, continued
• Polar water molecules pull ionic crystals apart, as
shown below.
• The partially negative oxygen atoms of water molecules
attract the positively charged sodium ions.
• The partially positive hydrogen atoms of water molecules
attract the negatively charged chloride ions.
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Chapter 7
Section 2 How Substances
Dissolve
Water: A Common Solvent, continued
• Water exhibits hydrogen bonding: the
intermolecular force occurring when a hydrogen
atom that is bonded to a highly electronegative atom
of one molecule is attracted to two unshared
electrons of another molecule.
• Hydrogen bonding determines many of water’s
unique properties.
• Hydrogen bonding enables water to dissolve many
molecular compounds, such as sugar.
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Chapter 7
Section 2 How Substances
Dissolve
Water: A Common Solvent, continued
• A rule of thumb in chemistry is that like dissolves like.
• This rule means that a solvent will dissolve
substances that are like the solvent in
molecular structure.
• A nonpolar compound is a compound whose
electrons are equally distributed among its atoms.
• A nonpolar compound usually will not dissolve in
water, because its intermolecular forces do not
match with those of water.
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Chapter 7
Section 2 How Substances
Dissolve
Like Dissolves Like
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Chapter 7
Section 2 How Substances
Dissolve
The Dissolving Process
• According to the kinetic theory of matter, water
molecules in a glass of tea are always moving.
• When sugar is poured into the tea, water molecules
collide with sugar molecules.
• Sugar molecules form a solution with water
molecules at the surface of the sugar crystals.
• As layers of sugar molecules leave the crystal, more
layers are uncovered and dissolve among the
solvent (water) molecules in the same way.
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Chapter 7
Section 2 How Substances
Dissolve
The Dissolving Process, continued
• Solutes with a larger surface area dissolve faster.
• More solute particles are exposed to the solvent.
• Stirring or shaking a solution helps the solute
dissolve faster.
• Dissolved solute particles diffuse throughout the
solution faster, allowing more solute particles to
dissolve.
• Solutes dissolve faster when the solvent is hot.
• Collisions occur between solute and solvent
particles more frequently and with more energy.
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Chapter 7
Section 2 How Substances
Dissolve
Surface Area
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Chapter 7
Section 2 How Substances
Dissolve
The Dissolving Process, continued
• Solutes affect the physical properties of a solution.
• Examples:
• If you dissolve salt in water, it will boil at a
higher temperature and freeze at a lower
temperature.
• The coolant mixture of
ethylene glycol (antifreeze)
with water keeps a car’s
radiator fluid from freezing in
winter or boiling in summer.
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Chapter 7
Section 3 Solubility and
Concentration
Objectives
• Explain the meaning of solubility and compare the
solubilities of various substances.
• Describe dilute, concentrated, saturated, and
supersaturated solutions.
• Relate changes in temperature and pressure to
changes in solubility of solid and gaseous solutes.
• Express the concentration of a solution as molarity,
and calculate the molarity of a solution given the
amount of solute and the volume of the solution.
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Chapter 7
Section 3 Solubility and
Concentration
Solubility in Water
• Solubility is the maximum amount of a solute that
will dissolve in a given quantity of solvent at a given
temperature and pressure.
• Some substances, such as oil, are insoluble in
water, meaning they never dissolve.
• Other substances are said to be soluble in water
because they dissolve easily in water.
• However, there is often a limit to how much of a
substance will dissolve.
• Different substances have different solubilities.
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Chapter 7
Section 3 Solubility and
Concentration
Solubility in Water, continued
• To express how much of a substance can dissolve in
a solvent, you need to use the concentration.
• Concentration is the amount of a particular
substance in a given volume of solution.
• A solution whose ratio of solute to solvent is
relatively high is referred to as concentrated.
• A solution whose ratio of solute to solvent is
relatively low is referred to dilute.
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Chapter 7
Section 3 Solubility and
Concentration
Solubility in Water, continued
• An unsaturated solution contains less than the
maximum amount of solute that can dissolve.
• A saturated solution is at a point where no more
solute can be dissolved under the same conditions.
• If you add more solute to a saturated solution, it will simply
fall to the bottom of the container.
• A supersaturated solution holds more dissolved
solute than is required to reach equilibrium at a given
temperature.
• To make a supersaturated solution, you raise the
temperature of a solution, dissolve more solute, then
let the solution cool again.
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Chapter 7
Section 3 Solubility and
Concentration
Solubility in Water, continued
• Gases can also dissolve in water.
• Unlike solid solutes, gaseous solutes are less soluble
in warmer water than they are in colder water.
• Example: Soda goes flat quickly at room temperature.
• The solubility of gases also depends on pressure.
Lowered pressure of gas above a solution leads to
dissolved gas bubbling out of the solution.
• Example: When a can of soda is opened, carbon dioxide gas
that had been dissolved in the soda bubbles out of solution.
• Example: If a scuba diver surfaces too quickly, dissolved
nitrogen gas in the bloodstream bubbles out of solution,
which causes a painful condition called the bends.
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Chapter 7
Section 3 Solubility and
Concentration
Concentration of Solutions
• There are several ways to express the concentration
of solutions, but one of the most useful ways is by
using molarity: moles of dissolved solute per liter
of solution.
• Note that molarity is moles per liter of solution,
not per liter of solvent.
• A 1.0 M, which is read as “one molar,” solution of
NaCl, contains 1.0 mol of dissolved NaCl in every
1.0 L of solution.
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Chapter 7
Section 3 Solubility and
Concentration
Math Skills
Molarity Calculate the molarity of sodium carbonate,
Na2CO3, in a solution of 38.6 g of solute in 0.500 L
of solution.
1. List the given and unknown values.
Given:
mass of sodium carbonate = 38.6 g
volume of solution = 0.500 L
Unknown: molarity, amount of Na2CO3 in 1 L
of solution
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Chapter 7
Section 3 Solubility and
Concentration
Math Skills, continued
2. Write the equation for moles Na2CO3 and molarity.
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Chapter 7
Section 3 Solubility and
Concentration
Math Skills, continued
3. Find the number of moles of Na2CO3 and
calculate molarity.
molarity of solution =
= 0.728 M
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Chapter 7
Section 3 Solubility and
Concentration
Concentration of Solutions, continued
• Other measures of solution concentration can
be used.
• These include:
• mass percent (grams of solute per 100 g
of solution)
• Ingredients in many food and household
products use mass percent.
• parts per million (grams of solute per 106 g
of solution)
• Used for very small concentrations, such
as for environmental regulations.
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