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Holt Chemistry

R.Thomas Myers, Keith Oldham,Savatore Tocci

Chapter 17

Oxidation, Reduction, and Electrochemistry

Educators


Problem 1

What is a redox reaction?

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Problem 2

Explain the terms oxidation and reduction in
terms of electrons.

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Problem 3

Explain how oxidation numbers are used to
identify redox reactions?

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Problem 4

Explain what half-reactions are and why
they are useful.

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Problem 5

Define electrochemistry.

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Problem 6

Define electrode, anode, and cathode.

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Problem 7

Explain voltage and current in terms of
electrons.

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Problem 8

Distinguish between galvanic and
electrolytic cells.

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Problem 9

What is a fuel cell?

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Problem 10

What is corrosion, and what is a
corrosion cell?

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Problem 11

Why does a sacrificial anode provide
cathodic protection?

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Problem 12

What is electroplating?

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Problem 13

Assign oxidation numbers to the atoms in
the ionic compound MgBr $_{2}(s) .$

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Problem 14

Assign oxidation numbers to the atoms in
the ionic compound $\mathrm{NH}_{4} \mathrm{NO}_{3}(s) .$

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Problem 15

Assign oxidation numbers to the atoms in
the ion $\mathrm{PF}_{6}^{-}(a q) .$

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Problem 16

Identify each of the following half-reactions
as oxidation or reduction reactions.
\begin{equation}
\begin{array}{l}{\text { a. } \mathrm{K}(s) \rightarrow e^{-}+\mathrm{K}^{+}(a q)} \\ {\text { b. } \mathrm{Cu}^{2+}(a q)+e^{-} \longrightarrow \mathrm{Cu}^{+}(a q)} \\ {\text { c. } \mathrm{Br}_{2}(l)+2 e^{-} \rightarrow 2 \mathrm{Br}^{-}(a q)}\end{array}
\end{equation}

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Problem 17

Is the reaction below a redox reaction?
Explain your answer.
$$\mathrm{Ca}(s)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{CaCl}_{2}(s)$$

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Problem 18

Describe how to identify the oxidizing agent
and the reducing agent in a reaction.

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Problem 19

Nitrogen monoxide, $\mathrm{NO}(g),$ reacts with
phosphorus, $\mathrm{P}_{4}(s)$ , to produce nitrogen,
$\mathrm{N}_{2}(g),$ and diphosphorus pentoxide, $\mathrm{P}_{2} \mathrm{O}_{5}$
Write the balanced equation for this reaction. Identify the atoms that have been
oxidized and reduced, and identify the
oxidizing and reducing agents.

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Problem 20

What is the distinction between a half-
reaction and an electrode reaction?

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Problem 21

Describe the components of an electro-
chemical cell.

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Problem 22

Identify which of the following reactions (as
written) is an anodic reaction and which is a
cathodic reaction. Write the balanced over-
all ionic equation for the redox reaction of
the cell.
$$\begin{array}{l}{\mathrm{Cd}(s) \rightarrow \mathrm{Cd}^{2+}(a q)+2 e^{-}} \\ {\mathrm{Ag}^{+}(a q)+e^{-} \rightarrow \mathrm{Ag}(s)}\end{array}$$

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Problem 23

What is the significance of the $\oplus$ symbol on
a dry cell or battery?

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Problem 24

What reaction happens at the cathode of an
electrochemical cell?

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Problem 25

In an electrochemical cell, what role does
the porous barrier play? What would happen without it?

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Problem 26

Explain why the combination of the two
electrode reactions of an electrochemical
cell always gives the equation of a redox
reaction.

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Problem 27

Describe a galvanic cell, and give an
example.

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Problem 28

Write the equations of the two electrode
reactions that occur when a Daniell cell is
in use. Identify the anode reaction and the
cathode reaction.

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Problem 29

What is the essential advantage of a fuel cell
over other types of galvanic cells that are
used to generate electrical energy?

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Problem 30

Explain why a corrosion cell is a galvanic
cell.

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Problem 31

Discuss methods of reducing corrosion.

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Problem 32

The standard electrode potential for the
reduction of $\mathrm{Zn}^{2+}(a q)$ to $\mathrm{Zn}(s)$ is $-0.762 \mathrm{V}$ .
What does this value indicate?

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Problem 33

Which half-reaction would be more likely to
be an oxidation: one with a standard electrode potential of $-0.42 \mathrm{V}$ , or one with a
standard electrode potential of $+0.42 \mathrm{V} ?$
Explain your answer.

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Problem 34

Define electrolytic cell, and give an example.

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Problem 35

Describe the apparatus used in the elec-
trolysis of water.

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Problem 36

Explain why sodium can be prepared by
electrolysis.

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Problem 37

Describe some benefits of electroplating.

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Problem 38

What are some problems in the electroplating industry?

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Problem 39

Determine the oxidation number of each
atom in $\mathrm{CO}_{2}$ .

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Problem 40

Determine the oxidation number of each
atom in CoO.

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Problem 41

Determine the oxidation number of each
atom in $\mathrm{BaCl}_{2} .$

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Problem 42

Determine the oxidation number of each
atom in $\mathrm{K}_{2} \mathrm{SO}_{4}$ .

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Problem 43

Determine the oxidation number of each
atom in $\mathrm{CaCO}_{3} .$

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Problem 44

Determine the oxidation number of each
atom in $\mathrm{PtCl}_{6}^{2-} .$

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Problem 45

Determine the oxidation number of each
atom in $\mathrm{COCl}_{2} .$

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Problem 46

Determine the oxidation number of each
atom in $\mathrm{PO}_{4}^{3-} .$

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Problem 47

Write the balanced half-reaction for the
conversion of $\mathrm{Fe}(s)$ to $\mathrm{Fe}^{2+}(a q) .$

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Problem 48

Write the balanced half-reaction for the
conversion of $\mathrm{Cl}_{2}(g)$ to $\mathrm{Cl}^{-}(a q) .$

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Problem 49

Combine the half-reactions from items 47
and 48 into a single reaction.

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Problem 50

Write the balanced half-reaction for the
conversion of $\operatorname{HOBr}(a q)$ to $\mathrm{Br}_{2}(a q)$ in acidic
solution.

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Problem 51

Write the balanced half-reaction for the
conversion of $\mathrm{H}_{2} \mathrm{O}(l)$ to $\mathrm{O}_{2}(a q)$ in acidic
solution.

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Problem 52

Combine the half-reactions from items 50
and 51 into a single reaction.

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Problem 53

Write the balanced half-reaction for the
change of $\mathrm{O}_{2}(a q)$ to $\mathrm{H}_{2} \mathrm{O}(l)$ in acidic
solution.

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Problem 54

Write the balanced half-reaction for the
change of $\mathrm{SO}_{2}(a q)$ to $\mathrm{HSO}_{4}^{-}(a q)$ in acidic
solution.

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Problem 55

Combine the reactions from items 53 and 54
into a single reaction.

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Problem 56

Using half-reactions, balance the redox
equation of $\mathrm{Zn}(s)$ and $\mathrm{Fe}^{3+}(a q)$ reacting
to form $\mathrm{Zn}^{2+}(a q)$ and $\mathrm{Fe}^{2+}(a q) .$

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Problem 57

The standard electrode potentials of two
electrodes in a cell are 1.30 $\mathrm{V}$ and 0.45 $\mathrm{V}$ .
What is the voltage of the cell?

Use the information from Table I to answer
the following items.

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Problem 58

Calculate the voltage of a cell for the naturally occurring reaction between the following electrodes:
\begin{equation}
\begin{array}{c}{\mathrm{AgCl}(s)+e^{-} \rightleftarrows \mathrm{Ag}(s)+\mathrm{Cl}^{-}(a q)} \\ {2 \mathrm{H}_{3} \mathrm{O}^{+}(a q)+2 e^{-} \rightleftarrows 2 \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{H}_{2}(g)}\end{array}
\end{equation}

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Problem 59

Calculate the voltage of a cell that has the
following electrode reactions:
\begin{equation}
\begin{array}{c}{2 \mathrm{H}_{3} \mathrm{O}^{+}(a q)+2 e^{-} \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{H}_{2}(g)} \\ {\mathrm{Fe}^{2+}(a q) \rightarrow \mathrm{Fe}^{3+}(a q)+e^{-}}\end{array}
\end{equation}

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Problem 60

Calculate the voltage of a cell in which the
overall reaction is
$$2 \mathrm{Fe}^{3+}(a q)+\mathrm{Cd}(s) \rightarrow \mathrm{Cd}^{2+}(a q)+2 \mathrm{Fe}^{2+}(a q)$$

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Problem 61

Calculate the voltage of a cell that has the
following electrode reactions:
$$\begin{array}{l}{\mathrm{O}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(l)+4 e^{-} \rightarrow 4 \mathrm{OH}^{-}(a q)} \\ {\mathrm{H}_{2}(g)+2 \mathrm{OH}^{-}(a q) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)+2 e^{-}}\end{array}$$

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Problem 62

Calculate the voltage of a cell in which the
two electrode reactions are the reduction of
chlorine gas to chloride ions and the oxidation of copper metal to copper( II) ions.

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Problem 63

Calculate the voltage of a cell in which the
two electrode reactions are those of the
lead-acid battery.

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Problem 64

Assign an oxidation number to the $\mathrm{N}$ atom:
in each of the following oxides of nitrogen:
$\mathrm{N}_{2} \mathrm{O}, \mathrm{NO}, \mathrm{NO}_{2}, \mathrm{N}_{2} \mathrm{O}_{3}, \mathrm{N}_{2} \mathrm{O}_{4},$ and $\mathrm{N}_{2} \mathrm{O}_{5} .$

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Problem 65

Refer to the figure below to answer the
following questions:
\begin{equation}
\begin{array}{l}{\text { a. What observations suggest that a chemi- }} \\ {\text { cal reaction has taken place? }} \\ {\text { b. Write a balanced equation for the }} \\ {\text { reaction taking place, and explain how }} \\ {\text { you can identify it as a redox reaction. }}\\{\text { d. Describe how the quantity of zinc metal }} \\ {\text { and of copper metal will change as the }} \\ {\text { reaction continues. }} \\ {\text { e. Describe the role of the chloride ions in }} \\ {\text { the reaction. }}\end{array}
\end{equation}

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Problem 66

What name is given to an electrode at which
oxidation occurs? at which reduction occurs?

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Problem 67

Using half-reactions, balance the equation
for the redox reaction when $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)$ and
$\mathrm{Fe}^{2+}(a q)$ react to form $\mathrm{Cr}^{3+}(a q)$ and
$\mathrm{Fe}^{3+}(a q)$ in acidic solution.

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Problem 68

Calculate the voltage of a cell in which the
overall reaction is the electrolysis of aqueous cadmium chloride into its elements.

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Problem 69

Calculate the voltage of a cell in which the
overall reaction is the electrolysis of solid
AgCl into its elements.

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Problem 70

Suggest how the word oxidation might have
come to be the general term for a loss of
electrons.

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Problem 71

Think of ammonium nitrite as $\left(\mathrm{NH}_{4}^{+}\right)\left(\mathrm{NO}_{2}^{-}\right)$
and assign oxidation numbers within each
ion. Now think of ammonium nitrate as
$\mathrm{N}_{2} \mathrm{H}_{4} \mathrm{O}_{2},$ and assign oxidation numbers.
Which assignment makes more sense?

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Problem 72

Why is the negative battery terminal the
one with the greater "electron pressure"?

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Problem 73

What is different about electric current in
metals compared with current in electrolyte
solutions?

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Problem 74

The activity of the halogens decreases as
you move down the group on the periodic
table. Use the information in Table 1 to
explain this trend.

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Problem 75

A fuel cell uses methanol, CH $_{3} \mathrm{OH},$ as fuel.
Assuming complete oxidation of the fuel to
$\mathrm{CO}_{2}$ and $\mathrm{H}_{2} \mathrm{O}$ in acidic aqueous solution,
how many electrons are transferred per
$\mathrm{CH}_{3} \mathrm{OH}$ molecule?

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Problem 76

Using Table $1,$ calculate the voltage of a cell
for the naturally occurring reaction between
the electrodes below. If a wire were connected between the Ag and Cu, which way
would electrons travel? Which electrode
would be the anode?
$\mathrm{Ag}^{+}(a q)+e^{-} \rightleftarrows \mathrm{Ag}(s)$
$\mathrm{Cu}^{2+}(a q)+2 e^{-} \rightleftarrows \mathrm{Cu}(s)$

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Problem 77

How does the oxidation number of an atom
of Mn change in the reaction below?
$$\begin{array}{r}{4 \mathrm{Mn}^{2+}(a q)+\mathrm{MnO}_{4}^{-}(a q)+8 \mathrm{H}_{3} \mathrm{O}^{+}(a q)+} \\ {15 \mathrm{H}_{2} \mathrm{P}_{4} \mathrm{O}_{7}^{2-}(a q) \rightarrow 12 \mathrm{H}_{2} \mathrm{O}(l)+} \\ {\quad 5 \mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{P}_{4} \mathrm{O}_{7}\right)_{3}^{3-}(a q)}\end{array}$$

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Problem 78

Consumer use of rechargeable batteries is
growing. Nickel-cadmium batteries, a common type of rechargeable battery, are used
in cellular phones, electric shavers, and
portable video-game systems. Make a list of
the items with which you come into contact
that use nickel-cadmium batteries or other
rechargeable batteries. Write a short essay
about technology that was not and could not
have been available before the development
of the nickel-cadmium battery.

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Problem 79

Read the book Apollo 13 on which the
movie of the same title was based, and
report information about the power sources
in the spacecraft.

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Problem 80

Research metals other than copper, sodium,
and aluminum that are manufactured or
refined electrochemically.

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Problem 81

Using a voltmeter from home or one bor-
rowed from your teacher, devise a method of
measuring the voltage of a flashlight battery
while it is delivering power to the bulb.
Compare that voltage with that of a new bat-
tery. Also record the voltage as the battery
"runs down." Write a report on your results.

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Problem 82

Manufacturers often claim that their batteries are "heavy duty" or "long lasting."
Design an experiment to test the value and
efficacy of AA batteries. If your teacher
approves, carry out your procedure.

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Problem 83

Carpentry nails are steel, but some are
plated with a second metal. Obtain a variety
of nails and evaluate their tendency to rust
by laying them on a piece of cloth moistened
by water containing salt and vinegar, so
they are exposed both to the liquid and to
air. After two weeks, report your findings.

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Problem 84

Use the following terms to create a concept
map: cathode, electrodes, electrochemical cell,
anode, oxidation, and reduction.

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Problem 85

What is the rate of production, in $\mathrm{g} / \mathrm{h},$ for
each metal?

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Problem 86

What is the rate of production, in mol/h, for
each metal?

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Problem 87

How much time is needed for 1.00 mol of
electrons to be absorbed?

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Problem 88

Write the half-reaction for the production
of silver metal from silver ions. Write the
half-reaction for the production of gold
metal from gold(III) ions. Using these half-
reactions, provide an explanation for the
difference in the rates of production of
the metals.

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Problem 89

Calculate the Equilibrium Constant, using
the Standard Cell Voltage

The graphing calculator can run a program
that calculates the equilibrium constant for
an electrochemical cell using an equation
called the Nernst equation, given the standard potential and the number of electrons
transferred. Given that the standard potential is 2.041 V and that two electrons are
transferred, you will calculate the equilibrium constant. The program will be used to
make the calculations.

Go to Appendix c. If you are using a TI-83
Plus, you can download the program
NERNST and data and run the application as
directed. If you are using another calculator,
your teacher will provide you with key-
strokes and data sets to use. After you
have run the program, answer the following
questions.

\begin{equation}
\begin{array}{l}{\text { a. What is the equilibrium constant when }} \\ {\text { the standard potential is } 0.099 ?} \\ {\text { b. What is the equilibrium constant when }} \\ {\text { the standard potential is } 1.125 ?} \\ {\text { c. What is the equilibrium constant when }} \\ {\text { the standard potential is } 2.500 ?}\end{array}
\end{equation}

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