Section 14.1

• An acid is a substance that produces hydronium ions (H3O+) when it dissolves in water.

• A hydronium ion (H3O+) consists of a

hydrogen ion (H+) attached to a water molecule (H2O).

Submicroscopic Behavior of Acids

Section 14.1

• Any hydrogen atom that can be transferred to water is called an acidic hydrogen.

Submicroscopic Behavior of Acids (cont.)

Section 14.1

Properties of Acids and Bases

• Acids taste sour.

• Bases taste bitter and usually have a slippery feel.

• The reactions of acids and bases are central to the chemistry of important living, environmental, and industrial processes.

Section 14.1

Properties of Acids and Bases (cont.)

Section 14.1

Properties of Acids and Bases (cont.)

• Litmus is a reliable indicator whether a substance is an acid (red) or a base (blue).

• An acid reacts with metals that are more active than hydrogen, or with carbonates.

• Bases do not commonly react with metals or carbonates.

litmus with base

litmus with acid

Section 14.1

– monoprotic—1 acidic hydrogen

– diprotic—2 acidic hydrogens

– polyprotic—more than 1 acidic hydrogen

Section 14.1

• Polyprotic acids lose their acidic hydrogens one at a time.

Submicroscopic Behavior of Acids (cont.)

Section 14.1

• The process of forming ions in solution is called ionization.

Submicroscopic Behavior of Acids (cont.)

• Because acids ionize to form ions in water, acidic solutions conduct electricity.

• Acids are electrolytes.

Section 14.1

Submicroscopic Behavior of Acids (cont.)

Section 14.1

• A base is a substance that produces hydroxide ions (OH–) when it dissolves in water.

• The simplest base is a water-soluble ionic compound that contains the hydroxide ion as the negative ion.

Submicroscopic Behavior of Bases

Section 14.1

• A few bases are covalent compounds that produce hydroxide ions by an ionization process when dissolved in water.

Submicroscopic Behavior of Bases (cont.)

• Because a base in water produces ions, it will conduct electricity.

Section 14.1

Submicroscopic Behavior of Bases (cont.)

A base can produce a hydroxide ion (OH-) by accepting a H+ from water

Section 14.1

• Due to the carbon dioxide in the atmosphere, rainwater is always slightly acidic but additional oxides such as sulfur and nitrogen create acid rain.

Acid Rain

Section 14.1

– Lime used to treat soil

CaO(s) + H2O(l) → Ca(OH)2(aq)

Ca(OH)2(aq) → Ca2+(aq) + 2OH–(aq)

– Soap

Na2O(s) + H2O(l) → 2Na(OH)(aq)

Na(OH)(aq) → Na+(aq) + OH–(aq)

Section 14.1

The Macroscopic-Submicroscopic Acid-Base Connection (cont.)

Section 14.2

The pH Scale

• The pH scale was created to make it easier to work with the large range of concentrations present in different acids and bases.

• pH is a mathematical scale in which the concentration of hydronium ions in a solution is expressed as a number from 0 to 14.

Section 14.2

The pH Scale (cont.)

• In the relationship between hydronium and hydroxide ions, as the concentration of one increases, the concentration of other must decrease.

Section 14.2

The pH Scale (cont.)

• Neutral solutions exist at a pH of 7, where hydronium and hydroxide ion concentrations are equal.

• Solutions with a pH lower than 7 have a higher concentration of hydronium ions and are acidic.

Section 14.2

The pH Scale (cont.)

• Solutions with a pH higher than 7 have a higher concentration of hydroxide ions and are basic.

Section 14.2

The pH Scale (cont.)

Section 14.2

Section Assessment

A base is a substance that produces ___ when it dissolves in water.

A. hydronium ions

B. electrolytes

C. hydroxide ions

D. polyprotic ions

Section 14.2

Section Assessment

An example of a base that accepts the transfer of a hydrogen ion when it is dissolved in water is:

A. ammonia

B. sodium hydroxide

C. calcium hydroxide

D. aluminum hydroxide

Section 14.1

Section Assessment

If a litmus strip turns blue, the substance must be a(n):

A. base

B. acid

Section 14.2

Strong Acids and Bases

• Acids and bases are categorized depending upon their strength, which is the degree to which they form ions.

Section 14.2

Strong Acids and Bases (cont.)

• A strong base is a base that completely dissociates into ions when dissolved in water.

• A strong acid is an acid that completely ionizes in water.

Section 14.2

Weak Acids and Bases

• A weak acid is an acid that only ionizes partially in solution.

Section 14.2

Weak Acids and Bases (cont.)

• The molecular structure of a weak acid determines the extent to which the acid ionizes in water.

Section 14.2

Weak Acids and Bases (cont.)

• A weak base ionizes only partially in solution. Most of the molecules do not react with water to form ions.

• The combination of strength and concentration ultimately determines the behavior of a solution.

• http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/acid13.swf

• Strong vs. weak acid

STP 3

What is a convenient way to compare the acidity and basicity of solutions?

A. pH scale

B. ionization indicator

C. pH table

D. neutrality diagram

Chapter Assessment 5

If a solution has a pH of 8, it is:

A. basic

B. acidic

C. neutral

STP 4

If a solution has a pH of 5, it is:

A. basic

B. acidic

C. neutral

Study Guide 1

Key Concepts

• The concentrations of hydrogen (H+) ions and hydroxide ions (OH–) determine whether an aqueous solution is acidic, basic or neutral.

• Acidic anhydrides are nonmetallic oxides that react with water to form acids. Basic anhydrides are metallic oxides that react with water to form bases.

Study Guide 2

Key Concepts

• Most acids and bases are weak. Only a small percentage of their molecules dissociate to form ions.

• The pH scale is a convenient way to compare the acidity and basicity of solutions.

• Acidic solutions have a pH less than 7, basic solutions have a pH greater than 7, and neutral solutions have a pH of exactly 7.