1. 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
9.4 Naming and Writing Formulas for
Acids and Bases
9.5 The Laws Governing How Compounds Form
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2. 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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3. Names and Formulas of Acids
How do you determine the name and formula of an acid?
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4. 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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5. 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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6. 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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7. 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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8. 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. 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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10. 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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11. 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
Anion ending
Example
Acid name
-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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12. CHEMISTRY & YOU
An acid that provides the crisp taste in many soft drinks has the formula H3PO4. What’s the name of this acid?
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13. The name of this acid is phosphoric acid.
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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14. 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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15. 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 (hydro- prefix and -ic suffix) must be a combination of hydrogen ion (H+) and bromide ion (Br –).
The formula is HBr.
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16. 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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17. 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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18. 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.
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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19. Name the following compounds as acids.
Sample Problem 9.8
Naming Acids
Name the following compounds as acids.
HClO
HCN
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20. Analyze Identify the relevant concepts.
Sample Problem 9.8
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. 1
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21. Solve Apply concepts to this problem.
Sample Problem 9.8 2
Solve Apply concepts to this problem.
Identify the anion in the acid and the suffix of the anion name.
a. HClO: ClO–, (hypochlorite)
b. HCN: CN–, (cyanide)
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22. Solve Apply concepts to this problem.
Sample Problem 9.8 2
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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23. What is the name of the acid H2S? (Hint: X = sulfide)
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24. 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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25. Names and Formulas of Bases
How do you determine the name and formula of a base?
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26. 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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27. 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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28. 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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29. 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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30. Name the following bases. KOH Fe(OH)2
Sample Problem 9.9
Naming Bases
Name the following bases.
KOH
Fe(OH)2
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31. Analyze Identify the relevant concepts.
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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32. Solve Apply the concepts to this problem.
Sample Problem 9.9 2
Solve Apply the concepts to this problem.
First, identify the cation and the anion in the compound.
KOH: cation: K+
anion: OH–
b. Fe(OH)2: cation: Fe2+
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33. Solve Apply the concepts to this problem.
Sample Problem 9.9 2
Solve Apply the concepts to this problem.
Now write the name of the cation, followed by the name of the anion.
KOH: cation: K+
anion: OH–
potassium hydroxide
b. Fe(OH)2: cation: Fe2+
iron(II) hydroxide
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34. 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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35. 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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36. 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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37. 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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38. 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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39. END OF 9.4
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