Chemistry for Changing Times
12th Edition
Hill and Kolb
Chapter 7
Acids and Bases:
Please Pass the Protons
John Singer
Jackson Community College, Jackson, MI
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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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Acids and Bases: Experimental
Definitions
Bases:
• Taste bitter.
• Turn litmus blue.
• Feel slippery.
• React with acids to form water and a salt.
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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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Acids, Bases, and Salts
Arrhenius Theory
Base: A substance that produces hydroxide
ions (OH-) in aqueous solution.
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Acids, Bases, and Salts
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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Acids, Bases, and Salts
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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Acids, Bases, and Salts
Brønsted-Lowry Theory
Acid: Proton donor
HA + H2O → H3O+ + ABase: Proton acceptor
NH3 + H2O → NH4+ + OH-
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Acids, Bases, and Salts
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 and Weak Acids and
Bases
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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Strong and Weak Acids and
Bases
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 AcidBase 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 AcidBase 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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Antacids: A Basic Remedy
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Antacids: A Basic Remedy
Substance
Formula
Product(s)
Sodium
bicarbonate
Calcium
carbonate
Aluminum
hydroxide
Magnesium
hydroxide
NaHCO3
Baking soda
CaCO3
Tums®
Al(OH)3
Amphojel®
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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Acids and Bases in Industry and
at Home
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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Acids and Bases in Industry and
at Home
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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Acids and Bases in Industry and
at Home
Soil can be
“sweetened” by
adding slaked lime
[Ca(OH)2].
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Acids and Bases in Industry and
at Home
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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Acids and Bases in Industry
and at Home
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.
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