Ch9.4Chem.ppt

(1)

9.4 Naming and Writing 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

(2)

>

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.

CHEMISTRY & YOU

(3)

>

Names and Formulas of Acids

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

Names and

Formulas of Acids

(4)

>

• 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.

Names and

Formulas of Acids

(5)

>

• Acids have many uses.

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

Names and

Formulas of Acids

(6)

>

• 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 H_nX, 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.

Names and

Formulas of Acids

(7)

>

• Three rules can help you name an acid with

the general formula H_nX 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.

Names and

Formulas of Acids

(8)

>

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

Names and

Formulas of Acids

(9)

>

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.

Names and

Formulas of Acids

(10)

>

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.

Names and

Formulas of Acids

(11)

>

Names and Formulas of AcidsNames and Formulas of Acids

These three rules for naming an acid with

the general formula H_nX 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 _hydro_chlor_ic_acid

-ite sulfite, SO₃– _(stem)-_ous _acid _sulfur_{ous acid}

(12)

>

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

CHEMISTRY & YOU

(13)

>

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

(14)

>

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.

Names and

Formulas of Acids

(15)

>

• 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–).

Names and

Formulas of Acids

(16)

>

• 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.

Names and

Formulas of Acids

(17)

>

• 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.

Names and

Formulas of Acids

(18)

>

Names and Formulas of AcidsNames and 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.

Writing Formulas of Acids

Common Acids

Name Formula

Hydrochloric acid HCl Sulfuric acid H₂SO₄

Nitric acid HNO₃ Ethanoic acid HC₂H₃O₂ Phosphoric acid H₃PO₄

(19)

>

Sample Problem 9.8Sample Problem 9.8

Naming Acids

Name the following compounds as acids.

(20)

>

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,

(21)

>

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)

(22)

>

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)

(23)

>

(24)

>

What is the name of the acid H₂S? (Hint: X = sulfide)

H₂S is named hydrosulfuric acid.

(25)

>

Names and Formulas of Bases

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

Names and Formulas

of Bases

(26)

>

• 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.

Names and Formulas

of Bases

(27)

>

• 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–).

Names and Formulas

of Bases

(28)

>

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.

Names and Formulas

of Bases

(29)

>

• 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.

Names and Formulas

of Bases

(30)

>

Naming Bases

Name the following bases. a. KOH

(31)

>

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.

(32)

>

Solve Apply the concepts to this problem.

First, identify the cation and the anion in the compound.

a. KOH: cation: K+

anion: OH–

(33)

>

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–

(34)

>

Is the naming of a base more similar to the naming of an acid or to the

(35)

>

Is the naming of a base more similar to the naming of an acid or to the

naming of other ionic compounds?

(36)

>

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

Key Concepts

(37)

>

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.

Key Concepts

(38)

>

• 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

Glossary Terms

(39)