Transcript Ch09 Lesson09_4

9.4 Naming and Writing
Formulas for Acids and Bases
>
Chapter 9
Chemical Names and Formulas
9.1 Naming Ions
9.2 Naming and Writing Formulas for Ionic
Compounds
9.3 Naming and Writing Formulas for Molecular
Compounds
9.4 Naming and Writing Formulas for
Acids and Bases
9.5 The Laws Governing How Compounds Form
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9.4 Naming and Writing
Formulas for Acids and Bases
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CHEMISTRY
& YOU
What’s the name
of the acid
responsible for the
crisp taste in this
drink?
There’s a certain
acid that gives
many soft drinks
their crisp,
enjoyable taste.
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9.4 Naming and Writing
Formulas for Acids and Bases
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Names and
Formulas of Acids
Names and Formulas of Acids
How do you determine the name and
formula of an acid?
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9.4 Naming and Writing
Formulas for Acids and Bases
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Names and
Formulas of Acids
• Acids are a group of ionic compounds with
unique properties.
• Acids can be defined in several ways.
• For now, it is enough to know that an
acid is a compound that contains one or
more hydrogen atoms and produces
hydrogen ions when dissolved in water.
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Formulas for Acids and Bases
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Names and
Formulas of Acids
• Acids have many uses.
• For example, sulfuric acid is often used
to etch circuit boards like the one shown
below.
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Formulas for Acids and Bases
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Names and
Formulas of Acids
• When naming an acid, you can consider the
acid to consist of an anion combined with as
many hydrogen ions as needed to make the
molecule electrically neutral.
• Therefore, the chemical formulas of acids
are in the general form HnX, where X is a
monatomic or polyatomic anion and n is a
subscript indicating the number of hydrogen
ions that are combined with the anion.
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Names and
Formulas of Acids
• Three rules can help you name an acid with
the general formula HnX dissolved in water.
• The naming system depends on the
name of the anion (X), in particular the
suffix of the anion name.
• Each rule deals with an anion with a
different suffix: -ide, -ite, and -ate.
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9.4 Naming and Writing
Formulas for Acids and Bases
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Names and
Formulas of Acids
• Three rules can help you name an acid with
the general formula HnX dissolved in water.
1. When the name of the anion ends in ide, the acid name begins with the
prefix hydro-. The stem of the anion
has the suffix -ic and is followed by
the word acid.
• Therefore, HCl (X= chloride) is named
hydrochloric acid.
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9.4 Naming and Writing
Formulas for Acids and Bases
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Names and
Formulas of Acids
• Three rules can help you name an acid with
the general formula HnX dissolved in water.
2. When the anion name ends in -ite,
the acid name is the stem of the
anion with the suffix -ous, followed
by the word acid.
• Thus, H2SO3 (X = sulfite) is named
sulfurous acid.
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9.4 Naming and Writing
Formulas for Acids and Bases
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Names and
Formulas of Acids
• Three rules can help you name an acid with
the general formula HnX dissolved in water.
3. When the anion name ends in -ate,
the acid name is the stem of the
anion with the suffix -ic, followed by
the word acid.
• Thus, HNO3 (X = nitrate) is named
nitric acid.
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Formulas for Acids and Bases
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Names and
Formulas of Acids
These three rules for naming an acid with
the general formula HnX dissolved in
water are summarized in the table below.
Naming Common Acids
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Anion
ending
Example
Acid name
Example
-ide
chloride, Cl–
hydro-(stem)-ic acid
hydrochloric acid
-ite
sulfite, SO3–
(stem)-ous acid
sulfurous acid
-ate
nitrate, NO3–
(stem)-ic acid
nitric acid
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9.4 Naming and Writing
Formulas for Acids and Bases
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CHEMISTRY
& YOU
An acid that provides the crisp taste in
many soft drinks has the formula H3PO4.
What’s the name of this acid?
12
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9.4 Naming and Writing
Formulas for Acids and Bases
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CHEMISTRY
& YOU
An acid that provides the crisp taste in
many soft drinks has the formula H3PO4.
What’s the name of this acid?
The name of this acid is phosphoric acid.
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Names and
Formulas of Acids
Writing Formulas of Acids
To write the formula for an acid, use
the rule for writing the name of the acid
in reverse. Then, balance the ionic
charges just as you would for any ionic
compound.
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Names and
Formulas of Acids
Writing Formulas of Acids
• For example, consider hydrobromic acid.
• Rule 1 states: When the name of the anion
ends in -ide, the acid name begins with the
prefix hydro-. The stem of the anion has the
suffix -ic and is followed by the word acid.
• Following Rule 1, hydrobromic acid (hydroprefix and -ic suffix) must be a combination of
hydrogen ion (H+) and bromide ion (Br –).
•
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The formula is HBr.
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Names and
Formulas of Acids
Writing Formulas of Acids
• How do you write the formula for phosphorous acid?
• Rule 2 states: When the anion name ends in -ite,
the acid name is the stem of the anion with the
suffix -ous, followed by the word acid.
• Using Rule 1, hydrogen ion and phosphite ion
(PO33–) must be the components of phosphorous
acid.
• You need three hydrogen ions to balance the
3– charge of the phosphite ion.
• Thus, the formula for phosphorous acid is
H3PO3.
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Names and
Formulas of Acids
Writing Formulas of Acids
• Finally, what is the formula for sulfuric acid?
• Rule 3 states: When the anion name ends in
-ate, the acid name is the stem of the anion with
the suffix -ic, followed by the word acid.
• According to Rule 3, sulfuric acid (-ic ending)
must be a combination of hydrogen ion and
sulfate ion (SO42–).
• The formula for sulfuric acid is H2SO4
because two hydrogen ions are needed to
balance the 2– charge of the sulfate anion.
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Names and
Formulas of Acids
Writing Formulas of Acids
• Many industrial
processes, including
steel and fertilizer
manufacturing, use
acids.
• You should become
familiar with the
names and formulas
of common acids
such as those listed
in the table at right.
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Common Acids
Name
Formula
Hydrochloric acid
HCl
Sulfuric acid
H2SO4
Nitric acid
HNO3
Ethanoic acid
HC2H3O2
Phosphoric acid
H3PO4
Carbonic acid
H2CO3
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Sample Problem 9.8
Naming Acids
Name the following compounds
as acids.
a. HClO
b. HCN
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Formulas for Acids and Bases
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Sample Problem 9.8
1 Analyze Identify the relevant concepts.
The anion of the acid determines the acid name.
(1) If the name of the anion ends in -ide, name
the acid using the stem of the anion with the
prefix hydro- and the suffix -ic, followed by the
word acid. (2) If the anion name ends in -ite,
name the acid using the stem of the anion with
the suffix -ous, followed by the word acid. (3) If
the anion name ends in -ate, name the acid
using the stem of the anion with the suffix -ic,
followed by the word acid.
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9.4 Naming and Writing
Formulas for Acids and Bases
2
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Sample Problem 9.8
Solve Apply concepts to this problem.
Identify the anion in the acid and the suffix of
the anion name.
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a. HClO:
ClO–, (hypochlorite)
b. HCN:
CN–, (cyanide)
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9.4 Naming and Writing
Formulas for Acids and Bases
2
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Sample Problem 9.8
Solve Apply concepts to this problem.
Name the acid using the appropriate prefix (if
any) and suffix. Finish with the word acid.
a. HClO:
ClO–, (hypochlorite)
hypochlorous acid (Rule 2)
b. HCN:
CN–, (cyanide)
hydrocyanic acid (Rule 1)
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What is the name of the acid H2S?
(Hint: X = sulfide)
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>
What is the name of the acid H2S?
(Hint: X = sulfide)
H2S is named hydrosulfuric acid.
Use Rule 1: When the name of the anion
ends in -ide, the acid name begins with the
prefix hydro-. The stem of the anion has the
suffix -ic and is followed by the word acid.
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9.4 Naming and Writing
Formulas for Acids and Bases
>
Names and Formulas
of Bases
Names and Formulas of Bases
How do you determine the name and
formula of a base?
25
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9.4 Naming and Writing
Formulas for Acids and Bases
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Names and Formulas
of Bases
• A base is generally an ionic compound that
produces hydroxide ions when dissolved in
water.
Bases are named in the same way as other
ionic compounds—the name of the cation
is followed by the name of the anion.
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9.4 Naming and Writing
Formulas for Acids and Bases
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Names and Formulas
of Bases
• The common base
sodium hydroxide is
used in making
cleaners, soap, and
paper, as shown in
the figure at right.
• Sodium hydroxide
(NaOH) is composed
of sodium cations
(Na+) and hydroxide
anions (OH–).
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9.4 Naming and Writing
Formulas for Acids and Bases
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Names and Formulas
of Bases
To write the formula for a base, first
write the symbol for the metal cation
followed by the formula for the
hydroxide ion. Then, balance the ionic
charges just as you would for any ionic
compound.
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9.4 Naming and Writing
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Names and Formulas
of Bases
• For example, aluminum hydroxide consists of
the aluminum cation (Al3+) and the hydroxide
anion (OH–).
• You need three hydroxide ions to balance the
3+ charge of the aluminum cation.
• Thus, the formula for aluminum hydroxide is
Al(OH)3.
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9.4 Naming and Writing
Formulas for Acids and Bases
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Sample Problem 9.9
Naming Bases
Name the following bases.
a. KOH
b. Fe(OH)2
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9.4 Naming and Writing
Formulas for Acids and Bases
>
Sample Problem 9.9
1 Analyze Identify the relevant concepts.
Bases are named like other ionic compounds—
the name of the cation is followed by the name of
the anion.
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9.4 Naming and Writing
Formulas for Acids and Bases
2
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Sample Problem 9.9
Solve Apply the concepts to this problem.
First, identify the cation and the anion in the
compound.
a. KOH:
cation: K+
anion: OH–
b. Fe(OH)2: cation: Fe2+
anion: OH–
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9.4 Naming and Writing
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2
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Sample Problem 9.9
Solve Apply the concepts to this problem.
Now write the name of the cation, followed by the
name of the anion.
a. KOH:
cation: K+
anion: OH–
potassium hydroxide
b. Fe(OH)2: cation: Fe2+
anion: OH–
iron(II) hydroxide
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Is the naming of a base more similar
to the naming of an acid or to the
naming of other ionic compounds?
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9.4 Naming and Writing
Formulas for Acids and Bases
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Is the naming of a base more similar
to the naming of an acid or to the
naming of other ionic compounds?
Unlike acids, bases are named in the
same way as other ionic compounds.
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9.4 Naming and Writing
Formulas for Acids and Bases
> Key Concepts
If the anion name ends in -ide, the acid
name begins with the prefix hydro-. The
stem of the anion has the suffix -ic and is
followed by the word acid. If the anion
name ends in -ite, the acid name is the
stem of the anion with the suffix
-ous, followed by the word acid. If the
anion name ends in -ate, the acid name is
the stem of the anion with the suffix
-ic, followed by the word acid. To write the
formula for an acid, use the rule for writing
the name of the acid in reverse.
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9.4 Naming and Writing
Formulas for Acids and Bases
> Key Concepts
Bases are named like other ionic
compounds. To write the formula for a
base, write the symbol for the metal cation
followed by that of the hydroxide ion.
Then, balance the ionic charges.
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9.4 Naming and Writing
Formulas for Acids and Bases
> Glossary Terms
• acid: a compound that produces hydrogen
ions in solution; see also hydrogen-ion
donor, Lewis acid
• base: a compound that produces
hydroxide ions in solution; see also
hydrogen-ion acceptor, Lewis base
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9.4 Naming and Writing
Formulas for Acids and Bases
>
END OF 9.4
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