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HIL04-124-167v4
1/13/04
12:10 PM
Page 159
Assessment Goals
159
Concept Review with Key Terms
4.1 Some Electrical Properties of Aqueous Solutions—Soluble
ionic compounds are completely dissociated into ions in aqueous solution and are therefore strong electrolytes. A few water-soluble molecular compounds are completely ionized in aqueous solution and are
also strong electrolytes. Most molecular compounds exist in solution
either as molecules (nonelectrolytes) or as a mixture of molecules and
ions (weak electrolytes).
+
–
– +
+
+ –
– + –
+
–
4.2 Reactions of Acids and Bases—A few
acids are strong acids; these acids are strong
electrolytes. However, most acids are weak
acids (weak electrolytes). The common strong
bases are water-soluble ionic hydroxides.
Weak bases, like the weak acids, are molecular compounds that exist as a mixture of molecules and ions in aqueous solution. Many common weak bases are related to ammonia.
Neutralization reactions between acids and bases are conveniently represented by ionic equations and net ionic equations. Net
ionic equations include only those ions that undergo a chemical reaction in solution; spectator ions are eliminated. The neutralization
reaction of an acid and a base produces water and an ionic compound
called a salt. The color of an indicator can be used to determine
whether a solution is acidic, basic, or neutral.
4.3 Reactions that Form Precipitates—
Another important type of reaction in solution
is one in which ions combine to form an insoluble solid—a precipitate. Solubility guidelines can often be used to predict precipitation
reactions (review Table 4.3). Qualitative and
quantitative chemical analyses and industrial
processes frequently make use of precipitation
reactions.
the reducing agent is oxidized. In a
Strength as a reducing agent
K
disproportionation reaction, the
Ca
Powerful
same substance acts as both oxidizing
Na
Mg
Strong
agent and reducing agent. Strong oxiAl
dizing agents include a few nonmetals
Cr
Good
Zn
and some species having atoms with
Fe
Cd
high oxidation numbers. Strong reFair
Ni
ducing agents include the active metSn
Pb
als and some species having atoms
H2
with low oxidation numbers. The
Poor
Cu
Ag
activity series of the metals ranks
Hg
metals in order of their strength as reVery poor
Au
ducing agents. It can be used to predict reactions between a metal and other metal ions in solution.
4.5 Applications of Oxidation and Reduction—
In everyday life, peroxides and hypochlorites are
encountered as oxidizing agents. In industry,
oxygen gas, chlorine, and chlorine-containing
compounds are used as oxidizing agents. Antioxidants such as vitamin C are reducing agents that
can scavenge reactive free radicals. Photosynthesis is an important redox reaction. Redox reactions are used in organic chemistry to oxidize alcohols to aldehydes
and ketones.
4.6 Titrations—A titration is a type of chemical analysis in which
two reactants are combined in exact stoichiometric proportions. In a
titration, the volume of a solution of known concentration (the titrant)
is added to a solution containing the analyte or sought-for substance.
The equivalence point occurs when the reactants are present in stoichiometric proportions. Often an indicator is used to render the
equivalence point visible through a color change. That color change
indicates the endpoint of the titration, Titrations can involve
acid–base reactions, precipitation reactions, or redox reactions.
4.4 Reactions Involving Oxidation and
Reduction—The oxidation number is the
charge on a monatomic ion; for species other than monatomic ions, it
is a hypothetical charge on an atom, assigned by a set of rules.
Oxidation is an increase in oxidation number accompanied by loss of
electrons. Reduction is a decrease in oxidation number accompanied
by gain of electrons. The two processes occur simultaneously in a
redox reaction. In a redox reaction, the oxidizing agent is reduced and
Assessment Goals
When you have mastered the material in this chapter, you will be
able to
• Identify strong electrolytes, weak electrolytes, and nonelectrolytes.
• Calculate ion concentrations in solutions of strong electrolytes.
• Classify a substance as an acid or base.
• Describe and identify strong and weak acids and strong and weak
bases.
• Describe neutralization reactions.
• Identify spectator ions in a solution. Write a net ionic equation for a
reaction in solution.
• Cite and use the solubility guidelines in Table 4.3.
• Predict whether precipitation will occur when certain ionic compounds are present in the same solution.
• Solve stoichiometry problems based on precipitation reactions.
• Assign oxidation numbers to elements in compounds or ions.
• Recognize a redox reaction, and determine whether the equation for
the reaction is balanced.
• Define and recognize oxidizing and reducing agents.
• Use the activity series to predict the products of redox reactions involving metals and metal ions.
• Describe some oxidation–reduction reactions of practical
significance.
• Describe how a titration is performed, and carry out calculations related to titrations.