Free Study Guide for
Cracolice • Peters
Introductory Chemistry: An Active Learning Approach
Second Edition
www.brookscole.com/chemistry
Chapter 19
Oxidation–Reduction
(Redox) Reactions
Chapter 19–Assignment A: Oxidation, Reduction, Redox. What Do They Mean?
An electron is transferred from a reducing agent to an oxidizing agent in an oxidationreduction reaction.
Look for the following big ideas in this assignment:
1)
Oxidation is a loss of electrons or an increase in oxidation number. Reduction is
a gain of electrons or a reduction in oxidation number.
2)
Oxidation-reduction (redox) reactions can be divided into an oxidation half-reaction
equation and a reduction half-reaction equation. Addition of these equations gives a
balanced equation for a redox reaction.
3)
In a redox reaction, the reducing agent (reducer) loses electrons and the oxidizing
agent (oxidizer) gains electrons.
Learning Procedures
Study
Sections 19.1–19.4. Focus on Goals 1–7 as you study.
Strategy
Definitions are critical here. Pay particular attention to bold-faced terms in
the textbook. The Oxidation Number Rules Summary is the key to Section
19.3.
Answer
Questions, Exercises, and Problems 1–15. Check your answers with those
at the end of the chapter.
Workbook
If your instructor recommends the Active Learning Workbook, do
Questions, Exercises, and Problems 1–15.
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Chapter 19
Oxidation–Reduction (Redox) Reactions
Chapter 19–Assignment B: Predicting Redox Reactions From Strengths of
Oxidizing and Reducing Agents
You can tell an oxidizer from a reducer, but so far, you cannot tell if a given oxidizer will
accept electrons from a given reducer. This assignment will teach you how to predict if a
redox reaction will occur when a given oxidizer and reducer are mixed. The new ideas to
look for in this assignment are:
1)
Strong oxidizing agents attract electrons strongly; weak oxidizers do not. Strong
reducing agents release electrons readily; weak reducers do not.
2)
The relative strengths of oxidizing and reducing agents may be determined from
their relative positions in a table.
3)
When a redox reaction reaches equilibrium, the weaker oxidizer and the weaker
reducer are favored.
Learning Procedures
Study
Sections 19.5–19.6. Focus on Goals 8–10 as you study. If you have already
studied Chapter 18, include Section 19.7 and Goal 11 in this assignment.
Strategy
The key to this assignment is learning how to use Table 19.2. Practice by
working the end-of-chapter questions.
Answer
Questions, Exercises, and Problems 16–20. Include Questions, Exercises,
and Problems 21 if you include Section 19.7 in this assignment. Check
your answers with those at the end of the chapter.
Workbook
If your instructor recommends the Active Learning Workbook, do
Questions, Exercises, and Problems 16–20. Include Questions, Exercises,
and Problems 21 if you include Section 19.7 in this assignment.
Chapter 19–Assignment C: Writing Redox Equations (Optional)
You have learned how to combine half-reaction equations to get a redox equation. However,
you haven't learned how to develop a half-reaction equation, knowing only the beginning
and final forms of the element oxidized or reduced.
It is quite easy to write a half-reaction equation when the element oxidized or reduced is not
combined with another element, either as a compound or ion. When the element oxidized or
reduced is so combined, however, a certain procedure must be followed. Learning that
procedure is the single new idea in this assignment.
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Study Guide for Introductory Chemistry: An Active Learning Approach
Learning Procedures
Study
Section 19.8. Focus on Goal 12 as you study.
Strategy
The Summary: Writing Redox Equations for Half-Reactions in Acidic
Solutions box outlines the procedure. Learn that, and then practice writing
equations.
Answer
Questions, Exercises, and Problems 22–26. Check your answers with those
at the end of the chapter.
Workbook
If your instructor recommends the Active Learning Workbook, do
Questions, Exercises, and Problems 22–26.
Chapter 19–Assignment D: Summary and Review
The vocabulary of redox reactions and equations is sometimes confusing because the terms
are so closely related. The following summary should help:
Redox Term
Change in Electrons
oxidation
loss of electrons
reduction
gain of electrons
oxidizing agent or oxidizer accepts electrons
reducing agent or reducer
donates electrons
Change in Oxidation Number
increase
decrease
decrease*
increase* (*monatomic species)
One way to remember these terms is to use the phrase LEO (THE LION) SAYS GER.
Lose Electrons = Oxidation. Gain Electrons = Reduction.
The key fact in combining half-reaction equations to get a redox reaction equation is that the
total number of electrons lost by one species must be gained by the other. The half-reaction
equations must be adjusted so that, when added, the electrons cancel out. If you must write a
half-reaction equation in which the element oxidized or reduced is combined with another
element on either side of the equation, follow exactly the procedure in the text.
Learning Procedures
Review
your lecture and textbook notes.
the Chapter in Review and the Key Terms and Concepts, and read the Study
Hints and Pitfalls to Avoid.
Answer
Concept-Linking Exercises 1–5. Check your answers with those at the end
of the chapter.
Questions, Exercises, and Problems 27–29. Include Questions 30–31 if
assigned by your instructor. Check your answers with those at the end of the
chapter.
Workbook
If your instructor recommends the Active Learning Workbook, do
Questions, Exercises, and Problems 27–29. Include Questions 30–31 if
assigned by your instructor.
140
Copyright © 2004 Brooks/Cole, a division of Thomson Learning, Inc.
No part of this work may be reproduced without the written permission of the publisher.
Chapter 19
Take
Oxidation–Reduction (Redox) Reactions
the chapter summary test that follows. Check your answers with those at the
end of this assignment.
Chapter 19 Sample Test
Questions 1 and 2: Use the following half-reactions.
Ca(s) Æ Ca2+(aq) + 2 e–
Al3+(aq) + 3 e– Æ Al(s)
1)
Identify the reduction half-reaction equation and the oxidation half-reaction
equation. Explain your reasoning.
2)
Rewrite the half-reaction equations in such form that they may be added to produce
a balanced redox equation. Write the balanced redox equation.
Questions 3–5: Use the following redox equation.
2 CrO4 2 –(aq) + 16 H+(aq) + 3 Cu(s) Æ 2 Cr3+(aq) + 3 Cu2+(aq) + 8 H2 O(l)
3)
The element that loses electrons is _______________.
Its oxidation number changes from _____ to _____.
4)
The element reduced is _______________.
Its oxidation number changes from _____ to _____.
5)
The oxidizing agent is _______________.
The reducing agent is _______________.
6)
If element Q is very likely to form Q– ions in a redox reaction, element Q is
a _________________________ agent.
a) strong reducing
b) strong oxidizing
c) weak reducing
d) weak oxidizing
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Study Guide for Introductory Chemistry: An Active Learning Approach
Questions 7–8: Use this hypothetical table
of relative strengths of oxidizers and reducers.
In this table, the strongest oxidizer is W.
W Æ W–
X+ Æ X
Y+ Æ Y
Z Æ Z–
7)
Identify the stronger oxidizer between Y+ and X+; identify the stronger reducer
between W– and Y.
8)
Determine whether or not each of the following redox reactions will proceed in the
forward direction.
a) Z + X D Z– + X+
b) X+ + Y D X + Y+
–
–
c) Z + W D Z + W
d) Y + Z D Y+ + Z–
e) X+ + W– D X + W
Question 9 is based on optional Section 19.8.
9)
Consider the redox reaction ClO3 – (aq) + I– (aq) Æ I2 (aq) + Cl– (aq)
a) Write the oxidation half-reaction equation.
b) Write the reduction half-reaction equation.
c) Add the half-reaction equations to produce a balanced redox equation.
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Chapter 19
Oxidation–Reduction (Redox) Reactions
Answers to Chapter 19 Sample Test
1)
The reduction half-reaction equation is Al3+(aq) + 3 e– Æ Al(s). The reactant gains
electrons. GER. The oxidation half-reaction equation is Ca(s) Æ Ca2+(aq) + 2 e– .
The reactant loses electrons. LEO.
2)
3 Ca(s) Æ 3 Ca2+(aq) + 6 e–
2 Al (aq) + 6 e– Æ 2 Al(s)
_______________________________________
3 Ca(s) + 2 Al3+(aq) Æ 3 Ca2+(aq) + 2 Al(s)
3)
The element that loses electrons is copper. Its oxidation number changes from 0 to
+2.
4)
The element reduced is chromium. Its oxidation number changes from +6 to +3.
5)
The oxidizing agent is CrO4 2 –. The reducing agent is Cu.
6)
b
7)
Stronger oxidizer: X+
8)
b and c will proceed in the forward direction.
9)
a)
b)
3+
c)
Stronger reducer: Y
3 [2 I– (aq) Æ I2 (aq) + 2 e– ]
6 e + ClO3 (aq) + 6 H+(aq) Æ Cl– (aq) + 3 H2 O(l)
_________________________________________________________
6 I– (aq) + ClO3 – (aq) + 6 H+(aq) Æ 3 I2 (aq) + Cl– (aq) + 3 H2 O(l)
–
–
143
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No part of this work may be reproduced without the written permission of the publisher.