Chemistry for Changing Times 12 th Edition Hill and Kolb Chapter 7 Acids and Bases: Please Pass the...

Chemistry for Changing Times12th Edition

Hill and Kolb

Chapter 7Acids and Bases:

Please Pass the ProtonsJohn Singer

Jackson Community College, Jackson, MI© 2010 Pearson Prentice Hall, Inc.

© 2010 Pearson Prentice Hall, 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.


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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.


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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


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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.


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Brønsted-Lowry Theory

Acid: Proton donor

HA + H2O → H3O+ + A-

Base: Proton acceptor

NH3 + H2O → NH4+ + OH-


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Brønsted-Lowry Theory


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Acidic and Basic Anhydrides

Anhydride means without water.

Nonmetal oxides are acidic anhydrides.

SO3 + H2O → H2SO4


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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 and Weak Acids and Bases

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)


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Strong bases ionize 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)


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


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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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Neutralization

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


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Neutralization

The amount of acid (or base) in a solution is determined by careful 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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The pH Scale

pH means “power” of hydrogen.

pH = -log[H+]


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The pH Scale


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Buffers and Conjugate Acid-Base Pairs

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).


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Buffers and Conjugate Acid-Base Pairs

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.


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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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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®


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Acids and Bases in Industry and at Home

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.


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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.


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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.


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


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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.


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


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Acids and Bases in Health and Disease

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.

Chemistry for Changing Times 12 th Edition Hill and Kolb Chapter 7 Acids and Bases: Please Pass the...

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