chapter 9 honclbrif chemical names and formulasweb.eccrsd.us/borda/public/honors/hc_ch9_4.pdf9.5 the...

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9.4 Naming and Writing Formulas for Acids and Bases

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Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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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> DIATOMICS

• HONClBrIF



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> Acids "  Binary Acids

"  H + one other element (nonmetal)

"  Ex: HF

"  hydrogen fluoride (use Ionic naming rules)

"  hydrofluoric acid (prefix hydro, -ic ending, “acid”)

"  “Acid” name is more commonly used

"  aqueous solutions (dissolved in water)


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> Acids "  Ternary Acids

"  H + polyatomic ion (>2 elements)

"  Ex: HNO3

•  Nitrate polyatomic ion = Nitric acid

•  Ex: HNO2

•  Nitrite polyatomic ion = Nitrous acid


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> Acids "  Ternary Acids

"  Exceptions:

"  HCN

"  ternary, but named like binary

"  “hydrocyanic acid” or “hydrogen cyanide”


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> Acids " HCl

"  HClO2

" HClO

"  H3PO4

"  H2CO3

"  H2SO3

"  H2S

"  Hydrochloric Acid or Hydrogen Chloride

" Chlorous Acid

" Hypochlorous Acid

"  Phosphoric Acid

"  Carbonic Acid

"  Sulfurous Acid

" Hydrosulfuric acid or Hydrogen Sulfide

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> Acids "  H2SO4

"  HC2H3O2

"  HClO4

"  H2CrO4

"  HF

"  H2C2O4

"  Sulfuric Acid

"  Acetic Acid

" Perchloric Acid

"  Chromic acid

"  Hydrofluoric Acid

"  Oxalic Acid


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Names and Formulas of Acids

How do you determine the name and formula of an acid?



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•  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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•  Acids have many uses.

•  For example, sulfuric acid is often used to etch circuit boards like the one shown below.



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•  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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•  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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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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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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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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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 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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An acid that provides the crisp taste in many soft drinks has the formula H3PO4. What’s the name of this acid?

CHEMISTRY & YOU 9.4 Naming and Writing Formulas for Acids and Bases

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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.

CHEMISTRY & YOU

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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.


Writing Formulas of Acids


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•  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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•  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 (PO3

3–) 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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•  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 (SO4

2–).

•  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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•  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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Sample Problem 9.8

Naming Acids

Name the following compounds as acids.

a.  HClO

b.  HCN

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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.

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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.

a. HClO: ClO–, (hypochlorite)

b. HCN: CN–, (cyanide)

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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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Names and Formulas of Bases

How do you determine the name and formula of a base?


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•  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.



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•  A common base, sodium hydroxide, is used in making cleaners, soap, and paper.

•  NaOH) •  (Na+) & (OH–)



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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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Sample Problem 9.9

Naming Bases

Name the following bases.

a.  KOH

b.  Fe(OH)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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chapter 9 honclbrif chemical names and formulasweb.eccrsd.us/borda/public/honors/hc_ch9_4.pdf9.5 the...

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