Chapter 7Acids and Bases

John Singer,

Jackson Community College

Chemistry for Changing Times,

Thirteenth Edition

Lecture Outlines

© 2013 Pearson Education, Inc.

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Acids and Bases: Experimental Definitions

Acids:• Taste sour.• Turn litmus red.• React with active metals to release hydrogen

gas.• React with bases to form water and a salt.

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Bases:

• Taste bitter.• Turn litmus blue.• Feel slippery.• React with acids to form water and a salt.

Acids and Bases: Experimental Definitions

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Acids and Bases: Experimental Definitions

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Acids, Bases, and Salts

Arrhenius Theory

Acid: A molecular substance that ionizes in aqueous solution to form hydrogen ions (H+).

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Arrhenius Theory

Base: A substance that produces hydroxide ions (OH-) in aqueous solution.

Acids, Bases, and Salts

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Neutralization: When an acid reacts with a base, the properties of each are neutralized and the products are water and a salt.

Acid + Base → Water + Salt

Acids, Bases, and Salts

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Limitations of the Arrhenius Theory• H+ ions do not exist in water solution. Protons

react with water to form hydronium ions (H3O+).

H+ + H2O → H3O+

• The Arrhenius theory does not explain the basicity of ammonia and similar compounds.

• It only applies to reactions in aqueous solution.

Acids, Bases, and Salts

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Brønsted-Lowry Theory

Acid: Proton donor

HCI + H2O → H3O+ + CI-

Base: Proton acceptor

NH3 + H2O → NH4+ + OH-

Acids, Bases, and Salts

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Brønsted-Lowry Theory

Acids, Bases, and Salts

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Salts are ionic compounds composed of cations other than hydrogen and anions other than hydroxide.

Acids, Bases, and Salts

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Anhydride means without water.

Nonmetal oxides are acidic anhydrides.

SO3 + H2O → H2SO4

Acids, Bases, and Salts

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Acidic and Basic Anhydrides

Metal oxides are basic anhydrides.

Example:

Lime (calcium oxide) reacts with water to form slaked lime (calcium hydroxide).

CaO + H2O → Ca(OH)2

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Strong acids ionize completely in water solution.

HCl(aq) → H+(aq) + Cl-(aq)

Weak acids only partially ionize in water solution.

HCN(aq) ↔ H+(aq) + CN-(aq)

Strong and Weak Acids and Bases

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Strong bases ionize or dissociate completely in water solution. NaOH(aq) → Na+(aq) + OH-(aq)

Weak bases only partially ionize in water solution. NH3(aq) + H2O ↔ NH4

+(aq) + OH-(aq)

Strong and Weak Acids and Bases

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Ammonia accepts a proton from water, forming a basic solution.

Strong and Weak Acids and Bases

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Neutralization

The reaction of an acid with a base is called neutralization. Water molecules are the result of the reaction between hydrogen ions and hydroxide ions.

H+ + OH- ↔ H2O

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During neutralization, an acid reacts with a base, forming water and a salt.

Neutralization

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The amount of acid (or base) in a solution is determined by careful neutralization.

Neutralization

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The pH Scale

pH is a means of expressing the acidity or basicity of a solution.

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pH means “power” of hydrogen.

pH = -log[H+]

The pH Scale

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The pH Scale

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Conjugate acid-base pairs are compounds or ions that differ by one proton (H+).

For example, the chloride ion (Cl-) is the conjugate base of the acid, hydrochloric acid (HCl).

Buffers and Conjugate Acid-Base Pairs

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Buffer solutions contain a weak acid and its conjugate base. Such solutions are capable of maintaining a nearly constant pH when small amounts of acid or base are added.

Buffers and Conjugate Acid-Base Pairs

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Acid Rain

Nonmetal oxides present in air react with water, forming acidic solutions. Rain with a pH of less than 5.6 is considered to be acid rain. Carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen monoxide (NO), and nitrogen dioxide (NO2) are the major nonmetallic oxides responsible for acid rain formation.

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Antacids: A Basic Remedy

Hyperacidity is when the stomach secretes too much acid. Antacids are often taken to neutralize excess acid and reduce the symptoms of hyperacidity.

Excessive use of antacids can lead to an increase in the pH of blood, a condition known as alkalosis.

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Antacids: A Basic Remedy

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Substance Formula Product(s)

Sodium bicarbonate

NaHCO3 Baking soda

Calcium carbonate

CaCO3 Tums®

Aluminum hydroxide

Al(OH)3 Amphojel®

Magnesium hydroxide

Mg(OH)2 Milk of Magnesia®

Antacids: A Basic Remedy

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Acid Reducers

Acid Reducers have been displacing antacids as a way to combat hyperacidity.

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Sulfuric acid is the leading chemical substance produced in the U.S. It is used to manufacture fertilizers and industrial chemicals. It is the acid of automotive batteries. Production is 40 billion kg/year.

Acids and Bases in Industry and at Home

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Hydrochloric acid has a number of uses. It is used as a rust remover, and it removes lime from mortar and household plumbing fixtures. It can be purchased from hardware stores as muriatic acid. Annual U.S. production is 4 billion kg.

Acids and Bases in Industry and at Home

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Lime (CaO) is produced by heating limestone (CaCO3).

CaCO3 + heat → CaO + CO2

Lime can be slaked by reacting with water to make calcium hydroxide (Ca(OH)2). Slaked lime is used to make mortar and cement and to sweeten soil. Annual U.S. production is 22 billion kg.

Acids and Bases in Industry and at Home

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Soil can be “sweetened” by adding slaked lime [Ca(OH)2].

Acids and Bases in Industry and at Home

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Sodium hydroxide, also known as lye, can be purchased for home use as oven cleaner or drain cleaners. It is used commercially to make soap. Annual U.S. production is 9 billion kg.

Acids and Bases in Industry and at Home

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Ammonia is produced for use as fertilizer and in household cleaning products. Production is about 11 billion kg/year.

Acids and Bases in Industry and at Home

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Concentrated acids and bases are corrosive to tissue and are health hazards. They can denature proteins in living cells.

The human body has wonderful mechanisms for maintaining the proper pH of tissue, blood, and body fluids.

Acids and Bases in Industry and at Home