Introductory Chemistry

Steven S. Zumdahl, Donald J. DeCoste

Chapter 18

Oxidation-Reduction Reactions and Electrochemistry - all with Video Answers

Educators

Chapter Questions

Problem 1

Give some examples of how we make good use of oxidation-reduction reactions in everyday life.

Lottie Adams

Lottie Adams

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Problem 2

How do chemists define the processes of oxidation and reduction? Write a simple equation illustrating each of your definitions.

Nicole Chung

Numerade Educator

Problem 3

For each of the following oxidation-reduction reactions, identify which element is being oxidized and which is being reduced.
a. $\mathrm{Cl}_{2}(g)+\mathrm{I}_{2}(g) \rightarrow 2 \mathrm{ICl}(g)$
b. $\mathrm{Cl}_{2}(g)+2 \mathrm{Li}(s) \rightarrow 2 \mathrm{LiCl}(s)$
c. $2 \mathrm{Na}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \rightarrow 2 \mathrm{NaOH}(a q)+\mathrm{H}_{2}(g)$
d. $\mathrm{Cl}_{2}(g)+2 \mathrm{NaBr}(a q) \rightarrow 2 \mathrm{NaCl}(a q)+\mathrm{Br}_{2}(l)$

Lottie Adams

Numerade Educator

Problem 4

For each of the following oxidation-reduction reactions, identify which element is oxidized and which is reduced.
a. $6 \mathrm{Na}(s)+\mathrm{N}_{2}(g) \rightarrow 2 \mathrm{Na}_{3} \mathrm{~N}(s)$
b. $\operatorname{Mg}(s)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{MgCl}_{2}(s)$
c. $2 \mathrm{Al}(s)+3 \mathrm{Br}_{2}(l) \rightarrow 2 \mathrm{AlBr}_{3}(s)$
d. $\mathrm{CuSO}_{4}(a q)+\mathrm{Mg}(s) \rightarrow \mathrm{MgSO}_{4}(a q)+\mathrm{Cu}(s)$

Lottie Adams

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Problem 5

For each of the following oxidation-reduction reactions, identify which element is being oxidized and which is being reduced.
a. $\mathrm{Ca}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{Ca}(\mathrm{OH})_{2}(s, a q)+\mathrm{H}_{2}(g)$
b. $\mathrm{H}_{2}(g)+\mathrm{F}_{2}(g) \rightarrow 2 \mathrm{HF}(g)$
c. $4 \mathrm{Fe}(s)+3 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{Fe}_{2} \mathrm{O}_{3}(s)$
d. $2 \mathrm{Fe}(s)+3 \mathrm{Cl}_{2}(g) \rightarrow 2 \mathrm{FeCl}_{3}(s)$

Lottie Adams

Numerade Educator

Problem 6

For each of the following oxidation-reduction reactions, identify which element is oxidized and which is reduced.
a. $\mathrm{Mg}(s)+\mathrm{Br}_{2}(l) \rightarrow \mathrm{MgBr}_{2}(s)$
b. $2 \mathrm{Na}(s)+\mathrm{S}(s) \rightarrow \mathrm{Na}_{2} \mathrm{~S}(s)$
c. $\mathrm{CO}_{2}(g)+\mathrm{H}_{2}(g) \rightarrow \mathrm{CO}(g)+\mathrm{H}_{2} \mathrm{O}(g)$
d. $6 \mathrm{~K}(s)+\mathrm{N}_{2}(g) \rightarrow 2 \mathrm{~K}_{3} \mathrm{~N}(s)$

Lottie Adams

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Problem 7

_________ lets us keep track of electrons in oxidation-reduction reactions by assigning charges to the various atoms in a compound.

Lottie Adams

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Problem 8

Why must the sum of all the oxidation states of the atoms in a neutral molecule be zero?

Kim Trang Nguyen

Kim Trang Nguyen

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Problem 9

Explain why, although it is not an ionic compound, we still assign oxygen an oxidation state of -2 in water, $\mathrm{H}_{2} \mathrm{O}$. Give an example of a compound in which oxygen is not in the -2 oxidation state.

Nicole Chung

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Problem 10

Why is fluorine always assigned an oxidation state of -1 ? What oxidation number is usually assigned to the other halogen elements when they occur in compounds? In an interhalogen compound involving fluorine (such as ClF ), which atom has a negative oxidation state?

Nicole Chung

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Problem 11

The sum of all the oxidation states of all the atoms in $\mathrm{H}_{3} \mathrm{PO}_{4}$ is ______

Nicole Chung

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Problem 12

What must be the sum of the oxidation states of all the atoms in a polyatomic ion? For example, the sum of all the oxidation states of all the atoms in $\mathrm{PO}_{4}^{3-}$ is .

Lottie Adams

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Problem 13

Assign oxidation states to all of the atoms in each of the following.
a. $\mathrm{CBr}_{4}$
b. $\mathrm{HClO}_{4}$
c. $\mathrm{K}_{3} \mathrm{PO}_{4}$
d. $\mathrm{N}_{2} \mathrm{O}$

Lottie Adams

Numerade Educator

Problem 14

Assign oxidation states to all of the atoms in each of the following.
a. $\mathrm{NBr}_{3}$
b. $\operatorname{SeF}_{6}$
c. $\mathrm{PBr}_{5}$
d. $\mathrm{CH}_{4}$

Lottie Adams

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Problem 15

What is the oxidation state of sulfur in each of the following substances?
a. $\mathrm{S}_{8}$
b. $\mathrm{H}_{2} \mathrm{SO}_{4}$
c. $\mathrm{NaHSO}_{4}$
d. $\mathrm{Na}_{2} \mathrm{~S}$

Lottie Adams

Numerade Educator

Problem 16

What is the oxidation state of nitrogen in each of the following substances?
a. $\mathrm{N}_{2}$
b. $\mathrm{NH}_{3}$
c. $\mathrm{NO}_{2}$
d. $\mathrm{NaNO}_{3}$

Lottie Adams

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Problem 17

What is the oxidation state of chlorine in each of the following substances?
a. ClF
b. $\mathrm{Cl}_{2}$
c. HCl
d. HClO

Lottie Adams

Numerade Educator

Problem 18

What is the oxidation state of manganese in each of the following substances?
a. $\mathrm{MnCl}_{2}$
b. $\mathrm{KMnO}_{4}$
c. $\mathrm{MnO}_{2}$
d. $\operatorname{Mn}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{3}$

Lottie Adams

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Problem 19

Assign oxidation states to all of the atoms in each of the following.
a. $\mathrm{CuCl}_{2}$
b. $\mathrm{KClO}_{3}$
c. $\mathrm{KClO}_{4}$
d. $\mathrm{Na}_{2} \mathrm{CO}_{3}$

Lottie Adams

Numerade Educator

Problem 20

Assign oxidation states to all of the atoms in each of the following.
a. $\mathrm{MgO}$
b. $\mathrm{Fe}_{2} \mathrm{O}_{3}$
c. $\mathrm{PCl}_{3}$
d. $\mathrm{N}_{2} \mathrm{O}_{5}$

Lottie Adams

Numerade Educator

Problem 21

Assign oxidation states to all of the atoms in each of the following ions:
a. $\mathrm{CO}_{3}^{2-}$
b. $\mathrm{NO}_{3}^{-}$
c. $\mathrm{PO}_{4}^{3-}$
d. $\mathrm{SO}_{4}^{2-}$

Lottie Adams

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Problem 22

Assign oxidation states to all of the atoms in each of the following ions.
a. $\mathrm{NH}_{4}^{+}$
b. $\mathrm{HCO}_{3}^{-}$
c. $\mathrm{OH}^{-}$
d. $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$

Lottie Adams

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Problem 23

Oxidation can be defined as a loss of electrons or as an increase in oxidation state. Explain why the two definitions mean the same thing, and give an example to support your explanation.

Nicole Chung

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Problem 24

Reduction can be defined as a gain of electrons or as a decrease in oxidation state. Explain why the two definitions mean the same thing, and give an example to support your explanation.

Nicole Chung

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Problem 25

What is an oxidizing agent? What is a reducing agent?

Nicole Chung

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Problem 26

Does an oxidizing agent increase or decrease its own oxidation state when it acts on another atom? Does a reducing agent increase or decrease its own oxidation state when it acts on another substance?

Abdel Osman

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Problem 27

Does an oxidizing agent donate or accept electrons? Does a reducing agent donate or accept electrons?

Nicole Chung

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Problem 28

The "Chemistry in Focus" segment Do We Age by Oxidation? discusses antioxidants. What does it mean for a chemical to be an antioxidant? How would it work chemically?

Nicole Chung

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Problem 29

In each of the following reactions, identify which element is being oxidized and which is being reduced by assigning oxidation numbers.
a. $\mathrm{Fe}(s)+\mathrm{CuSO}_{4}(a q) \rightarrow \mathrm{FeSO}_{4}(a q)+\mathrm{Cu}(s)$
b. $\mathrm{Cl}_{2}(g)+2 \mathrm{NaBr}(a q) \rightarrow 2 \mathrm{NaCl}(a q)+\mathrm{Br}_{2}(l)$
c. $3 \mathrm{CuS}(s)+8 \mathrm{HNO}_{3}(a q) \rightarrow 3 \mathrm{CuSO}_{4}(a q)+8 \mathrm{NO}(g)+4 \mathrm{H}_{2} \mathrm{O}(l)$
d. $2 \mathrm{Zn}(s)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{ZnO}(s)$

Lottie Adams

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Problem 30

In each of the following reactions, identify which element is being oxidized and which is being reduced by assigning oxidation numbers.
a. $2 \mathrm{Al}(s)+3 \mathrm{~S}(s) \rightarrow \mathrm{Al}_{2} \mathrm{~S}_{3}(s)$
b. $\mathrm{CH}_{4}(g)+2 \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)$
c. $2 \mathrm{Fe}_{2} \mathrm{O}_{3}(s)+3 \mathrm{C}(s) \rightarrow 3 \mathrm{CO}_{2}(g)+4 \mathrm{Fe}(s)$
d. $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}(a q)+14 \mathrm{HCl}(a q) \rightarrow 2 \mathrm{KCl}(a q)+2 \mathrm{CrCl}_{3}(s)+7 \mathrm{H}_{2} \mathrm{O}(l)+3 \mathrm{Cl}_{2}(g)$

Nicole Chung

Numerade Educator

Problem 31

In each of the following reactions, identify which element is being oxidized and which is being reduced by assigning oxidation states.
a. $2 \mathrm{Cu}(s)+\mathrm{S}(s) \rightarrow \mathrm{Cu}_{2} \mathrm{~S}(s)$
b. $2 \mathrm{Cu}_{2} \mathrm{O}(s)+\mathrm{O}_{2}(g) \rightarrow 4 \mathrm{CuO}(s)$
c. $4 \mathrm{~B}(s)+3 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{~B}_{2} \mathrm{O}_{3}(s)$
d. $6 \mathrm{Na}(s)+\mathrm{N}_{2}(g) \rightarrow 2 \mathrm{Na}_{3} \mathrm{~N}(s)$

Nicole Chung

Numerade Educator

Problem 32

In each of the following reactions, identify which element is being oxidized and which is being reduced by assigning oxidation numbers.
a. $4 \mathrm{KClO}_{3}(s)+\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s) \rightarrow 4 \mathrm{KCl}(s)+6 \mathrm{H}_{2} \mathrm{O}(l)+6 \mathrm{CO}_{2}(g)$
b. $2 \mathrm{C}_{8} \mathrm{H}_{18}(l)+25 \mathrm{O}_{2}(g) \rightarrow 16 \mathrm{CO}_{2}(g)+18 \mathrm{H}_{2} \mathrm{O}(l)$
c. $\mathrm{PCl}_{3}(g)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{PCl}_{5}(g)$
d. $\mathrm{Ca}(s)+\mathrm{H}_{2}(g) \rightarrow \mathrm{CaH}_{2}(g)$

Lottie Adams

Numerade Educator

Problem 33

Pennies in the United States consist of a zinc core that is electroplated with a thin coating of copper. Zinc dissolves in hydrochloric acid, but copper does not. If a small scratch is made on the surface of a penny, it is possible to dissolve away the zinc core, leaving only the thin shell of copper. Identify which element is oxidized and which is reduced in the reaction for the dissolving of the zinc by the acid.
$$
\mathrm{Zn}(s)+2 \mathrm{HCl}(a q) \rightarrow \mathrm{ZnCl}_{2}(a q)+\mathrm{H}_{2}(g)
$$

Nicole Chung

Numerade Educator

Problem 34

Iron ores, usually oxides of iron, are converted to the pure metal by reaction in a blast furnace with carbon (coke). The carbon is first reacted with air to form carbon monoxide, which in turn reacts with the iron oxides as follows:
$$
\mathrm{F}_{2} \mathrm{O}_{3}(s)+3 \mathrm{CO}(g) \rightarrow 2 \mathrm{Fe}(l)+3 \mathrm{CO}_{2}(g)
$$
Identify the atoms that are oxidized and reduced, and specify the oxidizing and reducing agents.

Nicole Chung

Numerade Educator

Problem 35

Although magnesium metal does not react with water at room temperature, it does react vigorously with steam at higher temperatures, releasing elemental hydrogen gas from the water.
$$
\mathrm{Mg}(s)+2 \mathrm{H}_{2} \mathrm{O}(g) \rightarrow \mathrm{Mg}(\mathrm{OH})_{2}(s)+\mathrm{H}_{2}(g)
$$
Identify which element is being oxidized and which is being reduced.

Nicole Chung

Numerade Educator

Problem 36

Potassium iodide in solution reacts readily with many reagents. In the following reactions, identify the atoms that are being oxidized and reduced, and specify the oxidizing and reducing agents.
a. $\mathrm{Cl}_{2}(g)+\mathrm{KI}(a q) \rightarrow \mathrm{KCl}(a q)+\mathrm{I}_{2}(s)$
b. $2 \mathrm{FeCl}_{3}(a q)+2 \mathrm{KI}(a q) \rightarrow 2 \mathrm{FeCl}_{2}(a q)+2 \mathrm{KCl}(a q)+\mathrm{I}_{2}(s)$
c. $2 \mathrm{CuCl}_{2}(a q)+4 \mathrm{KI}(a q) \rightarrow 2 \mathrm{CuI}(s)+4 \mathrm{KCl}(a q)+\mathrm{I}_{2}(s)$

Lottie Adams

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Problem 37

In what $t w o$ respects must oxidation-reduction reactions be balanced?

Lottie Adams

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Problem 38

Why is a systematic method for balancing oxidation-reduction reactions necessary? Why can't these equations be balanced readily by inspection?

Lottie Adams

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Problem 39

What is a half-reaction? What does each of the two half-reactions that make up an overall process represent?

Nicole Chung

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Problem 40

Why must the number of electrons lost in the oxidation equal the number of electrons gained in the reduction? Is it possible to have "leftover" electrons in a reaction?

Nicole Chung

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Problem 41

Balance each of the following half-reactions.
a. $\mathrm{Cu}(s) \rightarrow \mathrm{Cu}^{2+}(a q)$
b. $\mathrm{Fe}^{3+}(a q) \rightarrow \mathrm{Fe}^{2+}(a q)$
c. $\mathrm{Br}^{-}(a q) \rightarrow \mathrm{Br}_{2}(l)$
d. $\mathrm{Fe}^{2+}(a q) \rightarrow \mathrm{Fe}(s)$

Nicole Chung

Numerade Educator

Problem 42

Balance each of the following half-reactions.
a. $3 \mathrm{~N}_{2}(g)+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{~N}_{3}^{-}(a q)$
b. $\mathrm{O}_{2}^{2-}(a q) \rightarrow \mathrm{O}_{2}(g)$
c. $\mathrm{Zn}(s) \rightarrow \mathrm{Zn}^{2+}(a q)$
d. $\mathrm{F}_{2}(g) \rightarrow \mathrm{F}^{-}(a q)$

Lottie Adams

Numerade Educator

Problem 43

Balance each of the following half-reactions, which take place in acidic solution.
a. $\mathrm{HClO}(a q) \rightarrow \mathrm{Cl}^{-}(a q)$
b. $\mathrm{NO}(a q) \rightarrow \mathrm{N}_{2} \mathrm{O}(g)$
c. $\mathrm{N}_{2} \mathrm{O}(a q) \rightarrow \mathrm{N}_{2}(g)$
d. $\mathrm{ClO}_{3}^{-}(a q) \rightarrow \mathrm{HClO}_{2}(a q)$

Nicole Chung

Numerade Educator

Problem 44

Balance each of the following half-reactions, which take place in acidic solution.
a. $\mathrm{O}_{2}(g) \rightarrow \mathrm{H}_{2} \mathrm{O}(l)$
$\mathrm{b} . \mathrm{SO}_{4}^{2-}(a q) \rightarrow \mathrm{H}_{2} \mathrm{SO}_{3}(a q)$
c. $\mathrm{H}_{2} \mathrm{O}_{2}(a q) \rightarrow \mathrm{H}_{2} \mathrm{O}(l)$
d. $\mathrm{NO}_{2}^{-}(a q) \rightarrow \mathrm{NO}_{3}^{-}(a q)$

Nicole Chung

Numerade Educator

Problem 45

Balance each of the following oxidation-reduction reactions, which take place in acidic solution, by using the "half-reaction" method.
a. $\mathrm{Mg}(s)+\mathrm{Hg}^{2+}(a q) \rightarrow \mathrm{Mg}^{2+}(a q)+\mathrm{Hg}_{2}^{2+}(a q)$
b. $\mathrm{NO}_{3}^{-}(a q)+\mathrm{Br}^{-}(a q) \rightarrow \mathrm{NO}(g)+\mathrm{Br}_{2}(l)$
c. $\mathrm{Ni}(s)+\mathrm{NO}_{3}^{-}(a q) \rightarrow \mathrm{Ni}^{2+}(a q)+\mathrm{NO}_{2}(g)$
d. $\mathrm{ClO}_{4}^{-}(a q)+\mathrm{Cl}^{-}(a q) \rightarrow \mathrm{ClO}_{3}^{-}(a q)+\mathrm{Cl}_{2}(g)$

Lottie Adams

Numerade Educator

Problem 46

Balance each of the following oxidation-reduction reactions, which take place in acidic solution, by using the "half-reaction" method.
a. $\mathrm{Al}(s)+\mathrm{H}^{+}(a q) \rightarrow \mathrm{Al}^{3+}(a q)+\mathrm{H}_{2}(g)$
b. $\mathrm{S}^{2-}(a q)+\mathrm{NO}_{3}^{-}(a q) \rightarrow \mathrm{S}(s)+\mathrm{NO}(g)$
c. $\mathrm{I}_{2}(a q)+\mathrm{Cl}_{2}(a q) \rightarrow \mathrm{IO}_{3}^{-}(a q)+\mathrm{HCl}(g)$
d. $\mathrm{AsO}_{4}^{-}(a q)+\mathrm{S}^{2-}(a q) \rightarrow \mathrm{AsO}_{3}^{-}(a q)+\mathrm{S}(s)$

Lottie Adams

Numerade Educator

Problem 47

Iodide ion, $\mathrm{I}^{-}$, is one of the most easily oxidized species. Balance each of the following oxidation-reduction reactions, which take place in acidic solution, by using the "half-reaction" method.
a. $\mathrm{IO}_{3}^{-}(a q)+\mathrm{I}^{-}(a q) \rightarrow \mathrm{I}_{2}(a q)$
b. $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+\mathrm{I}^{-}(a q) \rightarrow \mathrm{Cr}^{3+}(a q)+\mathrm{I}_{2}(a q)$
c. $\mathrm{Cu}^{2+}(a q)+\mathrm{I}^{-}(a q) \rightarrow \mathrm{CuI}(s)+\mathrm{I}_{2}(a q)$

LM

Leslee Manner

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Problem 48

Nitric acid is a very strong acid, but is also a very strong oxidizing agent, and generally behaves as the latter. It will dissolve many metals. Balance the following oxidation-reduction reactions of nitric acid.
a. $\mathrm{Cu}(s)+\mathrm{HNO}_{3}(a q) \rightarrow \mathrm{Cu}^{2+}(a q)+\mathrm{NO}_{2}(g)$
b. $\mathrm{Mg}(s)+\mathrm{HNO}_{3}(a q) \rightarrow \mathrm{Mg}^{2+}(a q)+\mathrm{H}_{2}(g)$

Lottie Adams

Numerade Educator

Problem 49

Sketch a schematic representation of a typical galvanic cell, using a reaction of your choice. Indicate the direction of electron flow in your cell. How are the solutions placed in electrical contact to allow charge to balance between the chambers of the cell?

Nicole Chung

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Problem 50

What is a salt bridge? Why is a salt bridge necessary in a galvanic cell? Can some other method be used in place of the salt bridge?

Nicole Chung

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Problem 51

In which direction do electrons flow in a galvanic cell, from anode to cathode or vice versa?

Nicole Chung

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Problem 52

What type of reaction takes place at the cathode in a galvanic cell? At the anode?

Nicole Chung

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Problem 53

Consider the oxidation-reduction reaction
$$
\mathrm{Al}(s)+\mathrm{Ni}^{2+}(a q) \rightarrow \mathrm{Al}^{3+}(a q)+\mathrm{Ni}(s)
$$
Sketch a galvanic cell that makes use of this reaction. Which metal ion is reduced? Which metal is oxidized? What half-reaction takes place at the anode in the cell? What half-reaction takes place at the cathode?

Nicole Smina

Numerade Educator

Problem 54

Consider the oxidation-reduction reaction
$$
\mathrm{Zn}(s)+\mathrm{Pb}^{2+}(a q) \rightarrow \mathrm{Zn}^{2+}(a q)+\mathrm{Pb}(s)
$$
Sketch a galvanic cell that uses this reaction. Which metal ion is reduced? Which metal is oxidized? What half-reaction takes place at the anode in the cell? What half-reaction takes place at the cathode?

Nicole Smina

Numerade Educator

Problem 55

Write the chemical equation for the overall cell reaction that occurs in a lead storage automobile battery. What species is oxidized in such a battery? What species is reduced? Why can such a battery be "recharged"?

Nicole Chung

Numerade Educator

Problem 56

What are some advantages of using lithium ion batteries in electrical devices? What is a disadvantage?

Lottie Adams

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Problem 57

____ is the process of returning metals to their natural state-the ores from which they were originally obtained. This process involves ____ of the metal.

Lottie Adams

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Problem 58

Explain how some metals, notably aluminum, naturally resist complete oxidation by the atmosphere.

Nicole Chung

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Problem 59

Pure iron ordinarily rusts quickly, but steel does not corrode nearly as fast. How does steel resist corrosion?

Nicole Chung

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Problem 60

The "Chemistry in Focus" segment Stainless Steel: It's the Pits discusses the fact that stainless steel can corrode if there is a deficit of chromium. How does chromium protect stainless steel?

Lottie Adams

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Problem 61

How does an electrolysis cell differ from a galvanic cell?

Ronald Prasad

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Problem 62

What are some important uses of electrolysis?

Lottie Adams

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Problem 63

Although aluminum is one of the most abundant metals on earth, its price until the $1890 \mathrm{~s}$ made it a "precious metal" like gold and platinum. Why?

Ronald Prasad

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Problem 64

The "Chemistry in Focus" segment Water-Powered Fireplace discusses a fireplace that uses the electrolysis of water to produce hydrogen gas. Write the balanced chemical equation for the electrolysis of water. Which element in water is oxidized? Which is reduced? Find the oxidation states to answer these questions. Also, how is heat generated by the fireplace?

Lottie Adams

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Problem 65

Reactions in which one or more ____ are transferred between species are called oxidation-reduction reactions.

Lottie Adams

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Problem 66

Another name for the term oxidation state is ____.

Lottie Adams

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Problem 67

Reduction may be described as a(n) ____ of electrons or as a decrease in ____

Ronald Prasad

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Problem 68

In assigning oxidation states for a covalently bonded molecule, we assume that the more element controls both electrons of the covalent bond.

Ronald Prasad

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Problem 69

69. The sum of the oxidation states of the atoms in a polyatomic ion is equal to the overall ____ of the ion.

Lottie Adams

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Problem 70

What is an oxidizing agent? Is an oxidizing agent itself oxidized or reduced when it acts on another species?

Ronald Prasad

Numerade Educator

Problem 71

An oxidizing agent causes the (oxidation/reduction) of another species, and the oxidizing agent itself is (oxidized/reduced).

Ronald Prasad

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Problem 72

To function as a good reducing agent, a species must electrons easily.

Ronald Prasad

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Problem 73

When we balance an oxidation-reduction equation, the number of electrons lost by the reducing agent must ____ the number of electrons gained by the oxidizing
agent.

Lottie Adams

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Problem 74

To obtain useful electrical energy from an oxidation-reduction process, we must set up the reaction in such a way that the oxidation half-reaction and the reduction half-reaction are physically one another.

Lottie Adams

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Problem 75

75. An electrochemical cell that produces a current from an oxidation-reduction reaction is often called a(n) ____ cell.

Lottie Adams

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Problem 76

Which process (oxidation/reduction) takes place at the anode of a galvanic cell?

Ronald Prasad

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Problem 77

At which electrode (anode/cathode) do species gain electrons in a galvanic cell?

Ronald Prasad

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Problem 78

In a(n) cell, electrons flow through a wire from the reducing agent to the oxidizing agent.

Lottie Adams

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Problem 79

The "pressure" on electrons to flow from one electrode to the other in a battery is called the ____ of the battery.

Ronald Prasad

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Problem 80

The process of involves forcing a current through a cell to produce a chemical change that would not otherwise occur. How is this process different than what occurs in a galvanic cell?

Lottie Adams

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Problem 81

The common acid dry cell battery typically contains an inner casing made of ____ metal, which functions as the anode.

Ronald Prasad

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Problem 82

Corrosion of a metal represents its by species present in the atmosphere.

Ronald Prasad

Numerade Educator

Problem 83

Although aluminum is a reactive metal, pure aluminum ordinarily does not corrode severely in air because a protective layer of ____ builds up on the metal's surface.

Lottie Adams

Numerade Educator

Problem 84

For each of the following unbalanced oxidation-reduction chemical equations, balance the equation by inspection, and identify which species is the reducing agent.
a. $\mathrm{Fe}(s)+\mathrm{O}_{2}(g) \rightarrow \mathrm{Fe}_{2} \mathrm{O}_{3}(s)$
b. $\mathrm{Al}(s)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{AlCl}_{3}(s)$
c. $\mathrm{Mg}(s)+\mathrm{P}_{4}(s) \rightarrow \mathrm{Mg}_{3} \mathrm{P}_{2}(s)$

Lottie Adams

Numerade Educator

Problem 85

In each of the following reactions, identify which element is oxidized and which is reduced.
a. $\mathrm{Zn}(s)+2 \mathrm{HCl}(a q) \rightarrow \mathrm{ZnCl}_{2}(a q)+\mathrm{H}_{2}(g)$
b. $2 \mathrm{CuI}(s) \rightarrow \mathrm{CuI}_{2}(s)+\mathrm{Cu}(s)$
c. $6 \mathrm{Fe}^{2+}(a q)+\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+14 \mathrm{H}^{+}(a q) \rightarrow 6 \mathrm{Fe}^{3+}(a q)+2 \mathrm{Cr}^{3+}(a q)+7 \mathrm{H}_{2} \mathrm{O}(l)$

Ronald Prasad

Numerade Educator

Problem 86

In each of the following reactions, identify which species is the oxidizing agent.
a. $2 \mathrm{Al}(s)+6 \mathrm{HCl}(a q) \rightarrow 2 \mathrm{AlCl}_{3}(a q)+3 \mathrm{H}_{2}(g)$
b. $\mathrm{Cu}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{CuSO}_{4}(a q)+\mathrm{H}_{2}(g)$

Lottie Adams

Numerade Educator

Problem 87

Carbon compounds containing double bonds (such compounds are called alkenes) react readily with many other reagents. In each of the following reactions, identify which atoms are oxidized and which are reduced, and specify the oxidizing and reducing agents.
a. $\mathrm{CH}_{2}=\mathrm{CH}_{2}(g)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{ClCH}_{2}-\mathrm{CH}_{2} \mathrm{Cl}(l)$
b. $\mathrm{CH}_{2}=\mathrm{CH}_{2}(g)+\mathrm{Br}_{2}(g) \rightarrow \mathrm{BrCH}_{2}-\mathrm{CH}_{2} \mathrm{Br}(l)$
c. $\mathrm{CH}_{2}=\mathrm{CH}_{2}(g)+\mathrm{HBr}(g) \rightarrow \mathrm{CH}_{3}-\mathrm{CH}_{2} \mathrm{Br}(l)$
d. $\mathrm{CH}_{2}=\mathrm{CH}_{2}(g)+\mathrm{H}_{2}(g) \rightarrow \mathrm{CH}_{3}-\mathrm{CH}_{3}(g)$

Ronald Prasad

Numerade Educator

Problem 88

Balance each of the following oxidation-reduction reactions by inspection.
a. $\mathrm{C}_{3} \mathrm{H}_{8}(g)+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)$
b. $\mathrm{CO}(g)+\mathrm{H}_{2}(g) \rightarrow \mathrm{CH}_{3} \mathrm{OH}(l)$
c. $\operatorname{SnO}_{2}(s)+\mathrm{C}(s) \rightarrow \operatorname{Sn}(s)+\mathrm{CO}(g)$
d. $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(g)$

Lottie Adams

Numerade Educator

Problem 89

Balance each of the following oxidation-reduction reactions, which take place in acidic solution.
a. $\mathrm{MnO}_{4}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}_{2}(a q) \rightarrow \mathrm{Mn}^{2+}(a q)+\mathrm{O}_{2}(g)$
b. $\mathrm{BrO}_{3}^{-}(a q)+\mathrm{Cu}^{+}(a q) \rightarrow \mathrm{Br}^{-}(a q)+\mathrm{Cu}^{2+}(a q)$
c. $\mathrm{HNO}_{2}(a q)+\mathrm{I}^{-}(a q) \rightarrow \mathrm{NO}(g)+\mathrm{I}_{2}(a q)$

Lottie Adams

Numerade Educator

Problem 90

For each of the following oxidation-reduction reactions of metals with nonmetals, identify which element is oxidized and which is reduced.
a. $4 \mathrm{Na}(s)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{Na}_{2} \mathrm{O}(s)$
b. $\mathrm{Fe}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow \mathrm{FeSO}_{4}(a q)+\mathrm{H}_{2}(g)$
c. $2 \mathrm{Al}_{2} \mathrm{O}_{3}(s) \rightarrow 4 \mathrm{Al}(s)+3 \mathrm{O}_{2}(g)$
d. $3 \mathrm{Mg}(s)+\mathrm{N}_{2}(g) \rightarrow \mathrm{Mg}_{3} \mathrm{~N}_{2}(s)$

Lottie Adams

Numerade Educator

Problem 91

For each of the following oxidation-reduction reactions of metals with nonmetals, identify which element is oxidized and which is reduced.
a. $3 \mathrm{Zn}(s)+\mathrm{N}_{2}(g) \rightarrow \mathrm{Zn}_{3} \mathrm{~N}_{2}(s)$
b. $\operatorname{Co}(s)+\mathrm{S}(s) \rightarrow \operatorname{CoS}(s)$
c. $4 \mathrm{~K}(s)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{~K}_{2} \mathrm{O}(s)$
d. $4 \mathrm{Ag}(s)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{Ag}_{2} \mathrm{O}(s)$

Lottie Adams

Numerade Educator

Problem 92

Assign oxidation states to all of the atoms in each of the following:
a. $\mathrm{NH}_{3}$
b. CO
c. $\mathrm{CO}_{2}$
d. $\mathrm{NF}_{3}$

Emily Wendel

Numerade Educator

Problem 93

Assign oxidation states to all of the atoms in each of the following:
a. $\mathrm{PBr}_{3}$
b. $\mathrm{C}_{3} \mathrm{H}_{8}$
c. $\mathrm{KMnO}_{4}$
d. $\mathrm{CH}_{3} \mathrm{COOH}$

Ronald Prasad

Numerade Educator

Problem 94

Assign oxidation states to all of the atoms in each of the following:
a. $\mathrm{MnO}_{2}$
b. $\mathrm{BaCrO}_{4}$
c. $\mathrm{H}_{2} \mathrm{SO}_{3}$
d. $\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}$

Emily Wendel

Numerade Educator

Problem 95

Assign oxidation states to all of the atoms in each of the following:
a. $\mathrm{CrCl}_{3}$
b. $\mathrm{K}_{2} \mathrm{CrO}_{4}$
c. $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$
d. $\operatorname{Cr}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}$

Ronald Prasad

Numerade Educator

Problem 96

Assign oxidation states to all of the atoms in each of the following:
a. $\mathrm{BiO}^{+}$
b. $\mathrm{PO}_{4}^{3-}$
c. $\mathrm{NO}_{2}^{-}$
d. $\mathrm{Hg}_{2}^{2+}$

Emily Wendel

Numerade Educator

Problem 97

In each of the following reactions, identify which element is oxidized and which is reduced by assigning oxidation states.
a. $\mathrm{C}(s)+\mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)$
b. $2 \mathrm{CO}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{CO}_{2}(g)$
c. $\mathrm{CH}_{4}(g)+2 \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)$
d. $\mathrm{C}_{2} \mathrm{H}_{2}(g)+2 \mathrm{H}_{2}(g) \rightarrow \mathrm{C}_{2} \mathrm{H}_{6}(g)$

Ronald Prasad

Numerade Educator

Problem 98

In each of the following reactions, identify which element is oxidized and which is reduced by assigning oxidation states.
a. $2 \mathrm{~B}_{2} \mathrm{O}_{3}(s)+6 \mathrm{Cl}_{2}(g) \rightarrow 4 \mathrm{BCl}_{3}(l)+3 \mathrm{O}_{2}(g)$
b. $\mathrm{GeH}_{4}(g)+\mathrm{O}_{2}(g) \rightarrow \mathrm{Ge}(s)+2 \mathrm{H}_{2} \mathrm{O}(g)$
c. $\mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{Cl}_{2}(l)$
d. $\mathrm{O}_{2}(g)+2 \mathrm{~F}_{2}(g) \rightarrow 2 \mathrm{OF}_{2}(g)$

Ronald Prasad

Numerade Educator

Problem 99

Balance each of the following half-reactions.
a. $\mathrm{I}^{-}(a q) \rightarrow \mathrm{I}_{2}(s)$
b. $\mathrm{O}_{2}(g) \rightarrow \mathrm{O}^{2-}(s)$
c. $\mathrm{P}_{4}(s) \rightarrow \mathrm{P}^{3-}(s)$
d. $\mathrm{Cl}_{2}(g) \rightarrow \mathrm{Cl}^{-}(a q)$

Ronald Prasad

Numerade Educator

Problem 100

Balance each of the following half-reactions, which take place in acidic solution.
a. $\mathrm{SiO}_{2}(s) \rightarrow \mathrm{Si}(s)$
$\mathrm{b} . \mathrm{S}(s) \rightarrow \mathrm{H}_{2} \mathrm{~S}(a q)$
c. $\mathrm{NO}_{3}^{-}(a q) \rightarrow \mathrm{HNO}_{2}(a q)$
d. $\mathrm{NO}_{3}^{-}(a q) \rightarrow \mathrm{NO}(g)$

Ronald Prasad

Numerade Educator

Problem 101

Balance each of the following oxidation-reduction reactions, which take place in acidic solution, by using the "half-reaction" method.
a. $\mathrm{I}^{-}(a q)+\mathrm{MnO}_{4}^{-}(a q) \rightarrow \mathrm{I}_{2}(a q)+\mathrm{Mn}^{2+}(a q)$
b. $\mathrm{S}_{2} \mathrm{O}_{8}^{2-}(a q)+\mathrm{Cr}^{3+}(a q) \rightarrow \mathrm{SO}_{4}^{2-}(a q)+\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)$
c. $\mathrm{BiO}_{3}^{-}(a q)+\mathrm{Mn}^{2+}(a q) \rightarrow \mathrm{Bi}^{3+}(a q)+\mathrm{MnO}_{4}^{-}(a q)$

Lottie Adams

Numerade Educator

Problem 102

Consider a galvanic cell based on the following oxidation-reduction reaction:
$$
2 \mathrm{Al}^{3+}(a q)+3 \mathrm{Mg}(s) \rightarrow 2 \mathrm{Al}(s)+3 \mathrm{Mg}^{2+}(a q)
$$
What will the electrode found in the cathode portion of the cell be made of? Explain your answer.
a. air
b. HCl
c. Mg
d. Al
e. $\mathrm{H}_{2} \mathrm{SO}_{4}$

Lottie Adams

Numerade Educator

Problem 103

Consider the oxidation-reduction reaction
$$
\mathrm{Mg}(s)+\mathrm{Cu}^{2+}(a q) \rightarrow \mathrm{Mg}^{2+}(a q)+\mathrm{Cu}(s)
$$
Sketch a galvanic cell that uses this reaction. Which metal ion is reduced? Which metal is oxidized? What half-reaction takes place at the anode in the cell? What half-reaction takes place at the cathode?

Lottie Adams

Numerade Educator

Problem 104

The "Chemistry in Focus" segment Yellow Jeans? discusses the oxidation-reduction reaction required to turn the dye used in denim jeans from yellow to blue. The reaction is from leucoindigo to indigo. The reaction can be expressed as $\mathrm{Na}_{2} \mathrm{C}_{16} \mathrm{~N}_{2} \mathrm{H}_{10} \mathrm{O}_{2} \rightarrow \mathrm{C}_{16} \mathrm{~N}_{2} \mathrm{H}_{10} \mathrm{O}_{2} .$ Explain how from this reaction you know that
the leucindigo is oxidized to form indigo.

David Collins

Numerade Educator

Problem 105

Assign the oxidation state for the element listed in each of the following compounds:

Jennifer Hudspeth

Jennifer Hudspeth

Numerade Educator