Chemistry The Science in Context

Thomas R. Gilbert

Chapter 18

Electrochemistry: The Quest for Clean Energy - all with Video Answers

Educators

Chapter Questions

Problem 1

In the voltaic cell shown in Figure P18.1, the greater density of a concentrated solution of $\mathrm{CuSO}_{4}$ allows a less concentrated solution of $\mathrm{ZnSO}_{4}$ solution to be (carefully) layered on top of it. Why is a porous bridge not needed in this cell?
PICTURE CANT COPY

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 2

In the voltaic cell shown in Figure P18.2, the concentrations of $\mathrm{Cu}^{2+}$ and $\mathrm{Cd}^{2+}$ are $1.00 M .$ On the basis of the standard potentials in Appendix 6 , identify which electrode is the anode and which is the cathode. Indicate the direction of electron flow.
PICTURE CANT COPY

David Collins

Numerade Educator

Problem 3

In the voltaic cell shown in Figure $\mathrm{P} 18.3,\left[\mathrm{Ag}^{+}\right]=\left[\mathrm{H}^{+}\right]=$ $1.00 M$ and $P_{\mathrm{H}_{2}}=1.00$ atm. From the standard potentials in Appendix $6,$ Table $A 6.1,$ identify which electrode is the anode and which is the cathode. Indicate the direction of electron flow.
PICTURE CANT COPY

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 4

In many electrochemical cells the electrodes are metals that carry electrons to and from the cell but are not chemically changed by the cell reaction. Each of the highlighted clusters in the periodic table in Figure P18.4 consists of three metals. Which of the highlighted clusters is best suited to form inert electrodes?
GRAPH CANT COPY

David Collins

Numerade Educator

Problem 5

Which of the four curves in Figure P18.5 best represents the dependence of the potential of a lead-acid battery on the concentration of sulfuric acid? Note that the scale of the $x$ -axis is logarithmic.
FIGURE CANT COPY

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 6

Consider the four types of batteries in Figure $\mathrm{P} 18.6$ From top to bottom the sizes are $\mathrm{AAA}, \mathrm{AA}, \mathrm{C}$
and D. The performance of batteries such as these is
often expressed in units such as (a) volts, (b) watt-hours, or (c) milliampere-hours. Which of the values differ significantly between the four batteries?
PICTURE CANT COPY

David Collins

Numerade Educator

Problem 7

The apparatus in Figure P18.7 is used for the electrolysis of water. Hydrogen and oxygen gas are collected in the two inverted burettes. An inert electrode at the bottom of the left burette is connected
to the negative terminal of a 6-volt battery; the electrode in the burette on the right is connected to the positive terminal. A small quantity of sulfuric acid is added to speed up the electrolytic reaction.
a. What are the half-reactions at the left and right electrodes their standard potentials?

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 8

An electrolytic apparatus identical to the one shown in Problem 18.7 is used to electrolyze water, but the reaction is speeded up by the addition of sodium carbonate instead of sulfuric acid.
a. What are the half-reactions and the standard potentials for the electrodes on the left and right?
b. Why does sodium carbonate make the electrolysis reaction go more rapidly?

David Collins

Numerade Educator

Problem 9

Most classic cars, such as the one shown in Figure $\mathrm{P} 18.9$ have chromium-electroplated, or chrome, bumpers.
a. In the electroplating process is the bumper the anode or the cathode?
b. How does the presence of a layer of chromium protect the bumper from corroding?
picture cant copy

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 10

Use representations [A] through [I] in Figure P18.10 to answer questions a-f. The photo in image [E] shows silver deposited onto copper. If the materials in $[\mathrm{A}],[\mathrm{C}],[\mathrm{G}]$ and [I] were combined, along with a porous bridge and external circuit, to generate an electrochemical cell that produced [E]:
a. Which metal would be the cathode? Which solution would surround it?
b. Which metal would be the anode? Which solution would surround it?
c. When the reaction in $[\mathrm{E}]$ is finished, what will happen to the light blue color of the solution?
d. How could [E] be produced without a porous bridge or an external circuit?
e. Of the four particulate images $[\mathrm{B}],[\mathrm{D}]$ $[\mathrm{F}],$ and $[\mathrm{H}]$ in Figure $\mathrm{P} 18.10,$ which two correspond to the solutions $[\mathrm{G}]$ and $[\mathrm{I}] ?$
f. Which particulate image represents the copper wire with silver deposited onto it? What does the fourth particulate image depict?
PICTURE CANT COPY

David Collins

Numerade Educator

Problem 11

An element with a strong tendency to gain electrons is also ______
a. easily oxidized
b. a good oxidizing agent
c. a good reducing agent
d. a reactive metal

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 12

An element that is a good reducing agent is also ______
a. easily oxidized
b. a good oxidizing agent
c. easily reduced
d. a noble gas

David Collins

Numerade Educator

Problem 13

Regarding the porous separator between the two halves of an electrochemical cell:
a. Describe how it allows electrical charge to flow between the two half-cells.
b. Explain why a piece of wire could not perform the same function.

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 14

The Zn/Cu $^{2+}$ reactions in Figures 18.1 and 18.2 are the same; however, the reaction in the cell in Figure 18.2 generates electricity, whereas the reaction in the beaker in Figure 18.1 does not. Why?

David Collins

Numerade Educator

Problem 15

In the redox reaction below, how many moles of electrons are transferred for each mole of chlorine gas consumed?
$$2 \mathrm{Fe}^{2+}(a q)+\mathrm{Cl}_{2}(g) \rightarrow 2 \mathrm{Fe}^{3+}(a q)+2 \mathrm{Cl}^{-}(a q)$$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 16

In the redox reaction below, how many electrons are transferred for each molecule of $\mathrm{H}_{2} \mathrm{O}_{2}$ consumed?
$2 \mathrm{MnO}_{4}^{-}(a q)+3 \mathrm{H}_{2} \mathrm{O}_{2}(a q) \rightarrow$
$$2 \mathrm{MnO}_{2}(s)+3 \mathrm{O}_{2}(g)+2 \mathrm{OH}^{-}(a q)+2 \mathrm{H}_{2} \mathrm{O}(\ell)$$

David Collins

Numerade Educator

Problem 17

Complete and balance the partial chemical equation below, using the appropriate half-reactions in Table $A 6.1$ for acidic solutions.
$$\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+\mathrm{Fe}^{2+}(a q) \rightarrow \mathrm{Cr}^{3+}(a q)+\mathrm{Fe}^{3+}(a q)$$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 18

Complete and balance the partial net ionic equation below, using the appropriate half-reactions in Table A6.1 for acidic solutions.
$$\mathrm{MnO}_{4}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}_{2}(a q) \rightarrow \mathrm{MnO}_{2}(s)+\mathrm{O}_{2}(g)$$

David Collins

Numerade Educator

Problem 19

Select the appropriate half-reactions from Appendix 6 to write net ionic equations describing the reaction between:
a. aluminum metal and $\mathrm{Fe}^{3+}$ ions in solution that produces dissolved $\mathrm{Al}^{3+}$ and $\mathrm{Fe}^{2+}$ ions.
b. $I_{2}$ and $N O_{2}^{-}$ ions in an alkaline solution that produces $\mathrm{I}^{-}$ and $\mathrm{NO}_{3}^{-}$ ions.
c. $\mathrm{MnO}_{4}^{-}$ and $\mathrm{Cr}^{3+}$ ions in an acidic solution that produces $\mathrm{Mn}^{2+}$ and $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$ ions.

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 20

Select the appropriate half-reactions from Appendix 6 to write net ionic equations describing the reaction between:
a. tin and $A g^{+}$ ions in solution that produces dissolved $\mathrm{Sn}^{2+}$ ions and silver metal.
b. copper and $\mathrm{O}_{2}$ in an acidic solution that produces $\mathrm{Cu}^{2+}$ ions.
c. solid $\mathrm{Cr}(\mathrm{OH})_{3}$ and $\mathrm{O}_{2}$ in a basic solution that produces $\mathrm{CrO}_{4}^{2-}$ ions.

David Collins

Numerade Educator

Problem 21

An electrochemical cell with an aqueous electrolyte is based on the reaction between $\mathrm{Ni}^{2+}(a q)$ and $\mathrm{Cd}(s)$ producing $\mathrm{Ni}(s)$ and $\mathrm{Cd}^{2+}(a q)$
a. Write half-reactions for the anode and cathode.
b. Write a balanced net ionic equation describing the cell reaction.
c. Draw the cell diagram.

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 22

A voltaic cell is based on the reaction between $\mathrm{Cu}^{2+}(a q)$ and $\mathrm{Ni}(s),$ producing $\mathrm{Cu}(s)$ and $\mathrm{Ni}^{2+}(a q)$
a. Write the anode and cathode half-reactions.
b. Write a balanced cell reaction.
c. Draw the cell diagram.

David Collins

Numerade Educator

Problem 23

A voltaic cell with a basic aqueous background electrolyte is based on the oxidation of $\mathrm{Cd}(s)$ to $\mathrm{Cd}(\mathrm{OH})_{2}(s)$ and the reduction of $\mathrm{MnO}_{4}^{-}(a q)$ to $\mathrm{MnO}_{2}(s)$
a. Write half-reactions for the cell's anode and cathode.
b. Write a balanced net ionic equation describing the cell reaction.
c. Draw the cell diagram.

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 24

A voltaic cell is based on the reduction of $\mathrm{Ag}^{+}(a q)$ to $\mathrm{Ag}(s)$ and the oxidation of $\operatorname{Sn}(s)$ to $\mathrm{Sn}^{2+}(a q)$
a. Write half-reactions for the cell's anode and cathode.
b. Write a balanced cell reaction.
c. Draw the cell diagram.

David Collins

Numerade Educator

Problem 25

Super Iron Batteries In $1999,$ scientists in Israel developed
a battery based on the following cell reaction with iron(VI), nicknamed "super iron":
$\beth \mathrm{K}_{2} \mathrm{FeO}_{4}(a q)+3 \mathrm{Zn}(s) \rightarrow \mathrm{Fe}_{2} \mathrm{O}_{3}(s)+\mathrm{ZnO}(s)+2 \mathrm{K}_{2} \mathrm{ZnO}_{2}(a q)$
a. Determine the number of electrons transferred in the cell reaction.
b. What are the oxidation states of the transition metals in the reaction?
c. Draw the cell diagram.

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 26

Aluminum-Air Batteries In recent years engineers have been working on an aluminum-air battery as an alternative energy source for electric vehicles. The battery consists of an aluminum anode, which is oxidized to solid aluminum hydroxide, immersed in an electrolyte of aqueous KOH. At the cathode oxygen from the air is reduced to hydroxide ions on an inert metal surface. Write the two half-reactions for the battery and diagram the cell. Use the generic $\mathrm{M}(s)$ symbol for the metallic cathode material.

David Collins

Numerade Educator

Problem 27

Which is a stronger oxidizing agent under standard conditions: oxygen or chlorine? Use the standard reduction potentials in Table $A 6.1$ to support your answer.

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 28

Of the group 1 elements $\mathrm{Li}, \mathrm{K},$ and $\mathrm{Na},$ which is the strongest reducing agent?

David Collins

Numerade Educator

Problem 29

Starting with the appropriate standard free energies of formation in Table A4.3 in Appendix 4, calculate the values of $\Delta G^{\circ}$ and $E_{\text {cell }}^{\circ}$ of the following reactions:
a. $2 \mathrm{Cu}^{+}(a q) \rightarrow \mathrm{Cu}^{2+}(a q)+\mathrm{Cu}(s)$
b. $\mathrm{Cu}(s)+2 \mathrm{Fe}^{3+}(a q) \rightarrow \mathrm{Cu}^{2+}(a q)+2 \mathrm{Fe}^{2+}(a q)$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 30

Starting with the appropriate standard free energies of formation in Appendix $4,$ calculate the values of $\Delta G^{\circ}$ and $E_{\text {cell of the following reactions: }}$
a. $2 \mathrm{Na}(s)+2 \mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow 2 \mathrm{NaOH}(a q)+\mathrm{H}_{2}(g)$
b. $2 \mathrm{Pb}(s)+\mathrm{O}_{2}(g)+2 \mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow$
$2 \mathrm{PbSO}_{4}(s)+2 \mathrm{H}_{2} \mathrm{O}(\ell)$

David Collins

Numerade Educator

Problem 31

If a piece of silver is placed in a solution in which $\left[\mathrm{Ag}^{+}\right]=\left[\mathrm{Cu}^{2+}\right]=1.00 \mathrm{M},$ will the following reaction
proceed spontaneously?
$$2 \mathrm{Ag}(s)+\mathrm{Cu}^{2+}(a q) \rightarrow 2 \mathrm{Ag}^{+}(a q)+\mathrm{Cu}(s)$$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 32

A piece of cadmium is placed in a solution in which $\left[\mathrm{Cd}^{2+}\right]=\left[\mathrm{Sn}^{2+}\right]=1.00 \mathrm{M} .$ Will the following reaction
proceed spontaneously?
$$\mathrm{Cd}(s)+\mathrm{Sn}^{2+}(a q) \rightarrow \mathrm{Cd}^{2+}(a q)+\mathrm{Sn}(s)$$

David Collins

Numerade Educator

Problem 33

Sometimes the anode half-reaction in the zinc-air battery (Figure 18.7 ) is written with the zincate ion, $\mathrm{Zn}(\mathrm{OH})_{4}^{2-}$ as the product. Write a balanced equation for the cell reaction based on this product.

Sima Sarker

Numerade Educator

Problem 34

Sometimes the cell reaction of nickel-cadmium batteries is written with Cd metal as the anode and solid $\mathrm{NiO}_{2}$ as the cathode. Assuming that the products of the reactions are a solid hydroxide of cadmium(II) at the anode and a solid hydroxide of nickel(II) at the cathode, write balanced equations for the cathode and anode half-reactions and the overall cell reaction.

David Collins

Numerade Educator

Problem 35

In a voltaic cell similar to the Cu-Zn cell in Figure $18.2,$ the Cu electrode is replaced with one made of Ni immersed in a solution of $\mathrm{NiSO}_{4} .$ Will the standard potential of this $\mathrm{Ni}-\mathrm{Zn}$ cell be greater than, the same as, or less than $1.10 \mathrm{V} ?$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 36

Suppose the copper half of the Cu-Zn cell in Figure 18.2 were replaced with a silver wire in contact with $1 M \mathrm{Ag}^{+}(a q)$
a. What would be the value of $E_{\text {cell }}^{\circ}$
b. Which electrode would be the anode?

David Collins

Numerade Educator

Problem 37

Starting with standard potentials listed in Table $\mathrm{A} 6.1$ calculate the values of $E_{\text {cell }}^{a}$ and $\Delta G^{\circ}$ of the following reactions.
a. $\mathrm{Cl}_{2}(g)+2 \mathrm{Br}^{-}(a q) \rightarrow \mathrm{Br}_{2}(\ell)+2 \mathrm{Cl}^{-}(a q)$
b. $\mathrm{Zn}(s)+\mathrm{Ni}^{2+}(a q) \rightarrow \mathrm{Zn}^{2+}(a q)+\mathrm{Ni}(s)$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 38

Voltaic cells based on the following pairs of half-reactions are constructed. For each pair, write a balanced equation for the cell reaction, and identify which half-reaction takes place at each anode and cathode.
a. $\mathrm{Cd}^{2+}(a q)+2 \mathrm{e}^{-} \rightarrow \mathrm{Cd}(s)$
$\mathrm{Ag}^{+}(a q)+\mathrm{e}^{-} \rightarrow \mathrm{Ag}(s)$
b. $\mathrm{AgBr}(s)+\mathrm{e}^{-} \rightarrow \mathrm{Ag}(s)+\mathrm{Br}^{-}(a q)$
$\mathrm{MnO}_{2}(s)+4 \mathrm{H}^{+}(a q)+2 \mathrm{e}^{-} \rightarrow \mathrm{Mn}^{2+}(a q)+2 \mathrm{H}_{2} \mathrm{O}(\ell)$
c. $\mathrm{PtCl}_{4}^{2-}(a q)+2 \mathrm{e}^{-} \rightarrow \mathrm{Pt}(s)+4 \mathrm{Cl}^{-}(a q)$
$\mathrm{AgCl}(s)+\mathrm{e}^{-} \rightarrow \mathrm{Ag}(s)+\mathrm{Cl}^{-}(a q)$

David Collins

Numerade Educator

Problem 39

Which of the following reductions will occur in the presence of $\mathrm{H}_{2}$ gas under standard conditions?
a. $A g^{+}$ to $A g$
b. $\mathrm{Mg}^{2+}$ to $\mathrm{Mg}$
c. $\mathrm{Cu}^{2+}$ to $\mathrm{Cu}$
d. $\mathrm{Cd}^{2+}$ to $\mathrm{Cd}$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 40

Which of the following oxidations will occur in the presence of $\mathrm{H}_{2}$ gas under standard conditions?
a. $\mathrm{Zn}^{2+}$ to $\mathrm{Zn}$
b. $\mathrm{Fe}^{2+}$ to $\mathrm{Fe}^{3+}$
c. $\mathrm{Cr}(\mathrm{OH})_{3}$ to $\mathrm{CrO}_{4}^{2-}$
d. Ni to Ni $^{2+}$

David Collins

Numerade Educator

Problem 41

The half-reactions and standard potentials for a nickelmetal hydride battery with a titanium-zirconium anode are as follows:
Cathode: $\quad \mathrm{NiO}(\mathrm{OH})(s)+\mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{e}^{-} \rightarrow \mathrm{Ni}(\mathrm{OH})_{2}(s)+\mathrm{OH}^{-}(a q)$
$E^{*}=0.52 \mathrm{V}$
Anode: $\quad \mathrm{TiZr}_{2} \mathrm{H}(s)+\mathrm{OH}^{-}(a q) \rightarrow \mathrm{TiZr}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(\ell)+\mathrm{e}^{-}$
$E^{\circ}=0.00 \mathrm{V}$
a. Write the overall cell reaction for this battery.
b. Calculate the standard cell potential.

Himanshu Kushwaha

Himanshu Kushwaha

Numerade Educator

Problem 42

Lithium-lon Batteries There are lithium-ion batteries that have cathodes composed of $\mathrm{FePO}_{4}$ when fully charged.
a. What is the formula of the cathode when the battery is fully discharged?
b. Is Fe oxidized or reduced as the battery discharges?
c. Is the cell potential of a lithium-ion battery with an iron phosphate cathode likely to differ from one with a cobalt oxide cathode? Explain your answer.

David Collins

Numerade Educator

Problem 43

The value of $E_{\text {cell for the reaction below is } 0.500 \mathrm{V} . \text { What is }}$ the value of $\Delta G_{\text {cell }}^{\text {? }}$
$$\mathrm{Mn}^{3+}+2 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{Mn}^{2+}+\mathrm{MnO}_{2}+4 \mathrm{H}^{+}$$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 44

What is the value of $\Delta G_{\text {cell }}^{\circ}$ for an electrochemical cell based on a cell reaction described by the following net ionic equation?
$$\mathrm{Mg}+2 \mathrm{Cu}^{+} \rightarrow \mathrm{Mg}^{2+}+2 \mathrm{Cu}$$

David Collins

Numerade Educator

Problem 45

For many years the $1.50 \mathrm{V}$ batteries used to power flashlights were based on the following cell reaction:
$\mathrm{Zn}(s)+2 \mathrm{NH}_{4} \mathrm{Cl}(s)+2 \mathrm{MnO}_{2}(s) \rightarrow$
$$\mathrm{Zn}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}(s)+\mathrm{Mn}_{2} \mathrm{O}_{3}(s)+\mathrm{H}_{2} \mathrm{O}(\ell)$$
What is the value of $\Delta G_{\text {cell }} ?$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 46

The first generation of laptop computers was powered by nickel-cadmium (nicad) batteries, which generated $1.20 \mathrm{V}$ in accordance with the following cell reaction:

David Collins

Numerade Educator

Problem 47

The cells in the nickel-metal hydride battery packs used in many hybrid vehicles produce $1.20 \mathrm{V}$ in accordance with the following cell reaction:
$$\mathrm{MH}(s)+\mathrm{NiO}(\mathrm{OH})(s) \rightarrow \mathrm{M}(s)+\mathrm{Ni}(\mathrm{OH})_{2}(s)$$
What is the value of $\Delta G_{\text {crli }} ?$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 48

A cell in a lead-acid battery delivers exactly $2.00 \mathrm{V}$ of cell potential in accordance with the following cell reaction:
$\mathrm{Pb}(s)+\mathrm{PbO}_{2}(s)+2 \mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow 2 \mathrm{PbSO}_{4}(s)+2 \mathrm{H}_{2} \mathrm{O}(\ell)$
What is the value of $\Delta G_{\text {cell }} ?$

David Collins

Numerade Educator

Problem 49

What is the function of platinum in the standard hydrogen electrode?

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 50

Platinum is very expensive, so why is it used in standard hydrogen standard electrodes where the half-reaction is $2 \mathrm{H}^{+}(a q)+2 \mathrm{e}^{-} \rightarrow \mathrm{H}_{2}(\mathrm{g}) ?$

David Collins

Numerade Educator

Problem 51

The potential of the standard hydrogen electrode (SHE) is the reference against which other half-reaction potentials are expressed. Why, then, is the SHE not widely used as a reference electrode in electrochemical cells?

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 52

Suggest a replacement metal for platinum in the standard hydrogen electrode. Explain why you selected the metal you did.

David Collins

Numerade Educator

Problem 53

An electrochemical cell consists of a standard hydrogen electrode and a second half-cell in which a magnesium electrode is immersed in a $1.00 M$ solution of $\mathrm{Mg}^{2+}$ ions.
a. What is the value of $E_{\text {cell }} ?$
b. Which electrode is the anode?
c. Which is a product of the cell reaction: $\mathrm{H}^{+}$ ions or $\mathrm{H}_{2}$ gas?

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 54

An electrochemical cell consists of a standard hydrogen electrode and a second half-cell in which a cadmium electrode is immersed in a $1.00 M$ solution of $\mathrm{Cd}^{2+}$ ions.
a. What is the value of $E_{\text {cell }} ?$
b. Which electrode is the anode?
c. Which is a product of the cell reaction: $\mathrm{Cd}^{2+}$ ions or $\mathrm{Cd}$ metal?

David Collins

Numerade Educator

Problem 55

Why does the operating cell potential of most batteries change little until the battery is nearly discharged?

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 56

The standard potential of the Cu-Zn cell reaction,
$$\mathrm{Zn}(s)+\mathrm{Cu}^{2+}(a q) \rightarrow \mathrm{Zn}^{2+}(a q)+\mathrm{Cu}(s)$$
is $1.10 \mathrm{V} .$ Would the potential of the Cu-Zn cell differ from $1.10 \mathrm{V}$ if the concentrations of both $\mathrm{Cu}^{2+}$ and $\mathrm{Zn}^{2+}$ were $0.25 M ?$

David Collins

Numerade Educator

Problem 57

If the potential of a hydrogen electrode based on the half-reaction
$$2 \mathrm{H}^{+}(a q)+2 \mathrm{e}^{-} \rightarrow \mathrm{H}_{2}(g)$$
is $0.000 \mathrm{V}$ at $\mathrm{pH}=0.00,$ what is the potential of the same electrode at $\mathrm{pH}=7.00 ?$

Narayan Hari

Numerade Educator

Problem 58

Glucose Metabolism The standard potentials for the reduction of nicotinamide adenine dinucleotide (NAD') and oxaloacetate (reactants in the multistep metabolism of glucose) are as follows:
$\mathrm{NAD}^{+}(a q)+2 \mathrm{H}^{+}(a q)+2 \mathrm{e}^{-} \rightarrow \mathrm{NADH}(a q)+\mathrm{H}^{+}(a q)$
$$
E^{*}=-0.320 \mathrm{V}
$$
Oxaloacetate $^{2-}(a q)+2 \mathrm{H}^{+}(a q)+2 \mathrm{e}^{-} \rightarrow$ malate $^{2-}(a q)$
$$
E^{\circ}=-0.166 \mathrm{V}
$$
a. Calculate the standard potential for the following reaction:
Oxaloacetate $^{2-}(a q)+\mathrm{NADH}(a q)+\mathrm{H}^{+}(a q) \rightarrow$
$$
\text { malate }^{-}(a q)+\mathrm{NAD}^{+}(a q)
$$
b. Calculate the equilibrium constant for the reaction at $25^{\circ} \mathrm{C}$

David Collins

Numerade Educator

Problem 59

Permanganate ion can oxidize sulfite to sulfate in basic solution as follows:
$$
\begin{aligned}
2 \mathrm{MnO}_{4}^{-}(a q)+3 \mathrm{SO}_{3}^{2-}(a q)+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow & \\
2 \mathrm{MnO}_{2}(s)+3 \mathrm{SO}_{4}^{2-}(a q)+2 \mathrm{OH}^{-}(a q)
\end{aligned}
$$
Determine the potential for the reaction $\left(E_{r x n}\right)$ at $25^{\circ} \mathrm{C}$ when the concentrations of the reactants and products are as follows: $\left[\mathrm{MnO}_{4}^{-}\right]=0.250 M,\left[\mathrm{SO}_{3}^{2-}\right]=0.425 \mathrm{M}$
$\left[\mathrm{SO}_{4}^{2-}\right]=0.075 M,$ and $\left[\mathrm{OH}^{-}\right]=0.0200 M .$ Will the
value of $E_{\mathrm{rxn}}$ increase or decrease as the reaction proceeds?

David Collins

Numerade Educator

Problem 60

A concentration cell can be constructed by using the same half-reaction for both the cathode and anode. What is the value of $E_{\text {cell }}$ for a concentration cell that combines copper electrodes in contact with $0.35 M$ copper (II) nitrate and $0.00075 M$ copper $(\mathrm{II})$ nitrate solutions?

David Collins

Numerade Educator

Problem 61

A copper penny dropped into a solution of nitric acid produces a mixture of nitrogen oxides. The following reaction describes the formation of NO, one of the products:
$3 \mathrm{Cu}(s)+8 \mathrm{H}^{+}(a q)+2 \mathrm{NO}_{3}^{-}(a q) \rightarrow$
$2 \mathrm{NO}(g)+3 \mathrm{Cu}^{2+}(a q)+4 \mathrm{H}_{2} \mathrm{O}(\ell)$
a. Starting with the appropriate standard potentials in Table A6.1, calculate $E_{\text {cell for this reaction. }}$
b. Calculate $E_{\text {cell }}$ at $25^{\circ} \mathrm{C}$ when $\left[\mathrm{H}^{+}\right]=0.500 M$ $\left[\mathrm{NO}_{3}^{-}\right]=0.0550 M,\left[\mathrm{Cu}^{2+}\right]=0.0500 M,$ and the
partial pressure of $\mathrm{NO}=0.00250$ atm.

Shubham Kumar

Numerade Educator

Problem 62

Chlorine dioxide $\left(\mathrm{ClO}_{2}\right)$ is produced by the following reaction of chlorate $\left(\mathrm{ClO}_{3}^{-}\right)$ with $\mathrm{Cl}^{-}$ in acid solution:
$\begin{aligned} 2 \mathrm{ClO}_{3}^{-}(a q)+2 \mathrm{Cl}^{-}(a q)+4 \mathrm{H}^{+}(a q) \rightarrow & \\ 2 \mathrm{ClO}_{2}(g)+\mathrm{Cl}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(\ell) \end{aligned}$
a. Determine $E^{\circ}$ for the reaction.
b. The reaction produces a mixture of gases in the reaction vessel in which $P_{\mathrm{C} 10_{2}}=2.0 \mathrm{atm} ; P_{\mathrm{C}_{2}}=1.00 \mathrm{atm}$
Calculate $\left[\mathrm{ClO}_{3}^{-}\right]$ if, at equilibrium $\left(T=25^{\circ} \mathrm{C}\right),\left[\mathrm{H}^{+}\right]=$
$\left[\mathrm{Cl}^{-}\right]=10.0 \mathrm{M}$

Eileen Sullivan

Eileen Sullivan

Numerade Educator

Problem 63

One 12 -volt lead-acid battery has a higher ampere-hour rating than another. Which of the following parameters are likely to be different for the two batteries?
a. individual cell potentials
b. anode half-reactions
c. total masses of electrode materials
d. number of cells
e. electrolyte composition
f. combined surface areas of their electrodes

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 64

In a voltaic cell based on the Cu-Zn cell reaction
$$
\mathrm{Zn}(s)+\mathrm{Cu}^{2+}(a q) \rightarrow \mathrm{Cu}(s)+\mathrm{Zn}^{2+}(a q)
$$
there is exactly 1 mole of each reactant and product. A second cell based on the Cd-Cu cell reaction
$$
\mathrm{Cd}(s)+\mathrm{Cu}^{2+}(a q) \rightarrow \mathrm{Cu}(s)+\mathrm{Cd}^{2+}(a q)
$$
also has exactly 1 mole of each reactant and product. Which of the following statements about these two cells is true?
a. Their cell potentials are the same.
b. The masses of their electrodes are the same.
c. The quantities of electrical charge that they can produce are the same.
d. The quantities of electrical energy that they can produce are the same.

David Collins

Numerade Educator

Problem 65

Which of the following voltaic cells will produce the greater quantity of electrical charge per gram of anode material?
$\mathrm{Cd}(s)+2 \mathrm{NiO}(\mathrm{OH})(s)+2 \mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow 2 \mathrm{Ni}(\mathrm{OH})_{2}(s)+\mathrm{Cd}(\mathrm{OH})_{2}(s)$
$\quad$ or
$\quad 4 \mathrm{Al}(s)+3 \mathrm{O}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(\ell)+4 \mathrm{OH}^{-}(a q) \rightarrow 4 \mathrm{Al}(\mathrm{OH})_{4}^{-}(a q)$

David Collins

Numerade Educator

Problem 66

Which of the following voltaic cells will produce the greater quantity of electrical charge per gram of anode material?
$$\mathrm{Zn}(s)+\mathrm{MnO}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow \mathrm{ZnO}(s)+\mathrm{Mn}(\mathrm{OH})_{2}(s)$$
or$$\mathrm{Li}(s)+\mathrm{MnO}_{2}(s) \rightarrow \mathrm{LiMnO}_{2}(s)$$

David Collins

Numerade Educator

Problem 67

Which of the following voltaic cells delivers more electrical energy per gram of anode material at $25^{\circ} \mathrm{C} ?$
$$
\begin{aligned}
\mathrm{Zn}(s)+2 \mathrm{NiO}(\mathrm{OH})(s)+2 \mathrm{H}_{2} \mathrm{O}(\ell) \rightarrow & \\
2 \mathrm{Ni}(\mathrm{OH})_{2}(s)+\mathrm{Zn}(\mathrm{OH})_{2}(s) & E_{\mathrm{cell}}^{\circ}=1.20 \mathrm{V}
\end{aligned}$$
Or$$\mathrm{Li}(s)+\mathrm{MnO}_{2}(s) \rightarrow \mathrm{LiMnO}_{2}(s) \quad E_{\mathrm{cell}}^{\circ}=3.15 \mathrm{V}$$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 68

Which of the following voltaic cell reactions delivers more electrical energy per gram of anode material at $25^{\circ} \mathrm{C} ?$
$$
\mathrm{Zn}(s)+\mathrm{Ni}(\mathrm{OH})_{2}(s) \rightarrow \mathrm{Zn}(\mathrm{OH})_{2}(s)+\mathrm{Ni}(s) \quad E_{\mathrm{cell}}^{*}=1.50 \mathrm{V}$$
or$$2 \mathrm{Zn}(s)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{ZnO}(s) \quad E_{\mathrm{cell}}^{\circ}=2.08 \mathrm{V}$$

David Collins

Numerade Educator

Problem 69

When the iron skeleton of the Statue of Liberty was replaced with stainless steel, the asbestos mats that had separated the skeleton from the copper exterior were replaced with Teflon spacers. Why was Teflon a good choice?

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 70

What does a sacrificial anode do to protect a metal structure, and why is the process called catbodic protection?

David Collins

Numerade Educator

Problem 71

Aquarium Windows The windows of the giant ocean tank at the New England Aquarium (Figure $\mathrm{P} 18.71$ ) are held in place with aluminum frames. What would be a good material to use to make sacrificial anodes for the frames?
PICTURE CANT COPY

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 72

The positive terminal of a voltaic cell is the cathode. However, the cathode of an electrolytic cell is connected to the negative terminal of a power supply. Explain this difference in polarity.

David Collins

Numerade Educator

Problem 73

The positive terminal of a voltaic cell is the cathode. However, the cathode of an electrolytic cell is connected to the negative terminal of a power supply. Explain this difference in polarity.

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 74

The anode in an electrochemical cell is defined as the electrode where oxidation takes place. Why is the anode in an electrolytic cell connected to the positive $(+)$ terminal of an external supply, whereas the anode in a voltaic cell battery is connected to the negative $(-)$ terminal?

David Collins

Numerade Educator

Problem 75

The salts obtained from the evaporation of seawater can be a source of halogens, principally $\mathrm{Cl}_{2}$ and $\mathrm{Br}_{2},$ through the electrolysis of the molten alkali metal halides. As the potential of the anode in an electrolytic cell is increased, which of these two halogens forms first?

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 76

Quantitative Analysis Electrolysis can be used to determinethe concentration of $\mathrm{Cu}^{2+}$ in a given volume of solution by electrolyzing the solution in a cell equipped with a platinum cathode. If all the $\mathrm{Cu}^{2+}$ is reduced to Cu metal at the cathode, the increase in mass of the electrode provides a measure of the concentration of $\mathrm{Cu}^{2+}$ in the original solution. To ensure the complete $(99.99 \%)$ removal of the $\mathrm{Cu}^{2+}$ from a solution in which $\left[\mathrm{Cu}^{2+}\right]$ is initially about 1.0 $M,$ will the potential of the cathode (versus SHE) have to be more or less negative than $0.34 \mathrm{V}$ (the standard potential for $\left.\mathrm{Cu}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Cu}\right) ?$

David Collins

Numerade Educator

Problem 77

A high school chemistry student wishes to demonstrate how water can be separated into hydrogen and oxygen by electrolysis. She knows that the reaction will proceed more rapidly if an electrolyte is added to the water. She has access to $2.00 M$ solutions of these compounds: $\mathrm{H}_{2} \mathrm{SO}_{4}$ $\mathrm{HBr}, \mathrm{NaI}, \mathrm{Na}_{2} \mathrm{SO}_{4},$ and $\mathrm{Na}_{2} \mathrm{CO}_{3} .$ Which one(s) should she use? Explain your selection(s).

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 78

A battery charger used to recharge the NiMH batteries used in a digital camera can deliver as much as 0.75 amperes of current to each battery. If it takes 100 min to recharge one battery, how many grams of $\mathrm{Ni}(\mathrm{OH})_{2}$ are oxidized to $\mathrm{NiO}(\mathrm{OH}) ?$

David Collins

Numerade Educator

Problem 79

A NiMH battery containing $4.10 \mathrm{g}$ of $\mathrm{NiO}(\mathrm{OH})$ was $75 \%$ discharged when it was connected to a charger with an output of $2.00 \mathrm{A}$ at $1.3 \mathrm{V} .$ How long does it take to recharge the battery?

David Collins

Numerade Educator

Problem 80

How long does it take to deposit a coating of gold $1.00 \mu \mathrm{m}$ thick on a disk-shaped medallion $2.0 \mathrm{cm}$ in diameter and
$3.0 \mathrm{mm}$ thick at a constant current of $45 \mathrm{A} ?$ The density of gold is $18.3 \mathrm{g} / \mathrm{cm}^{3} .$ The gold solution contains gold( 111 ).

David Collins

Numerade Educator

Problem 81

Oxygen Supply in Submarines Nuclear submarines can stay under water nearly indefinitely because they can produce their own oxygen by the electrolysis of water.
a. How many liters of $\mathrm{O}_{2}$ at $25^{\circ} \mathrm{C}$ and 1.00 bar are produced in 1 hour in an electrolytic cell operating at a current of $0.025 \mathrm{A} ?$
b. Could seawater be used as the source of oxygen in this electrolysis? Explain why or why not.

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 82

In the electrolysis of water, how long will it take to produce $1.00 \times 10^{2} \mathrm{L}$ of $\mathrm{H}_{2}$ at $\mathrm{STP}(273 \mathrm{K} \text { and } 1.00 \mathrm{atm})$ by using
an electrolytic cell through which the current is 52 mA?

David Collins

Numerade Educator

Problem 83

Calculate the minimum (least negative) cathode potential (versus SHE) needed to begin electroplating nickel from $0.35 M \mathrm{Ni}^{2+}$ onto a piece of iron.

Aadit Sharma

Numerade Educator

Problem 84

What is the minimum (least negative) cathode potential (versus SHE) needed to electroplate silver onto cutlery in a solution of $\mathrm{Ag}^{+}$ and $\mathrm{NH}_{3}$ in which most of the silver ions are present as the complex, $\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}+$ and the concentration of $\mathrm{Ag}^{+}(a q)$ is only $2.50 \times 10^{-4} \mathrm{M} ?$

Nicole Smina

Numerade Educator

Problem 85

Describe two advantages of hybrid (gasoline engineelectric motor) power systems over all-electric systems based on fuel cells. Describe two disadvantages.

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 86

Describe three factors limiting widespread use of cars powered by fuel cells.

David Collins

Numerade Educator

Problem 87

Methane can serve as the fuel for electric cars powered by fuel cells. Carbon dioxide is a product of the fuel cell reaction. All cars powered by internal combustion engines burning natural gas (mostly methane) produce $\mathrm{CO}_{2}$. Why are electric vehicles powered by fuel cells likely to produce less $\mathrm{CO}_{2}$ per mile?

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 88

To make the refueling of fuel cells easier, several manufacturers offer converters that turn readily available fuels--such as natural gas, propane, and methanol-into $\mathrm{H}_{2}$ for the fuel cells and $\mathrm{CO}_{2}$. Although vehicles with such power systems are not truly "zero emission," they still offer significant environmental benefits over vehicles powered by internal combustion engines. Describe a few of those benefits.

David Collins

Numerade Educator

Problem 89

Fuel cells with molten alkali metal carbonates as electrolytes can use methane as a fuel. The methane is first converted into hydrogen in a two-step process:
$$
\begin{aligned}
\mathrm{CH}_{4}(g)+\mathrm{H}_{2} \mathrm{O}(g) & \rightarrow \mathrm{CO}(g)+3 \mathrm{H}_{2}(g) \\
\mathrm{CO}(g)+\mathrm{H}_{2} \mathrm{O}(g) & \rightarrow \mathrm{H}_{2}(g)+\mathrm{CO}_{2}(g)
\end{aligned}
$$
a. Assign oxidation numbers to carbon and hydrogen in the reactants and products.
b. Using the standard free energy of formation values in Table A4.3 in Appendix 4, calculate the standard free-energy changes in the two reactions and the overall $\Delta G^{\circ}$ for the formation of $\mathrm{H}_{2}+\mathrm{CO}_{2}$ from methane and
steam.

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 90

A direct methanol fuel cell uses the oxidation of methanol by oxygen to generate electrical energy. The overall reaction, which is given below, has a $\Delta G^{\circ}$ value of -702.4 kJ/mol of methanol oxidized. What is the standard cell potential for this fuel cell?
$$\mathrm{CH}_{3} \mathrm{OH}(\ell)+\frac{3}{2} \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(\ell)$$

David Collins

Numerade Educator

Problem 91

Calculate the $E_{\text {cell }}$ value at $298 \mathrm{K}$ for the cell based on the reaction
$$
\mathrm{Fe}^{3+}(a q)+\mathrm{Cu}^{+}(a q) \rightarrow \mathrm{Fe}^{2+}(a q)+\mathrm{Cu}^{2+}(a q)
$$
when $\left[\mathrm{Fe}^{3+}\right]=\left[\mathrm{Cu}^{+}\right]=1.50 \times 10^{-3} \mathrm{Mand}\left[\mathrm{Fe}^{2+}\right]=$
$\left[\mathrm{Cu}^{2+}\right]=2.5 \times 10^{-4} \mathrm{M}$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 92

Calculate the $E_{\text {cell value at } 298} \mathrm{K}$ for the cell based on the reaction
$$
mathrm{Cu}(s)+2 \mathrm{Ag}^{+}(a q) \rightarrow \mathrm{Cu}^{2+}(a q)+2 \mathrm{Ag}(s)$$
when $\left[\mathrm{Ag}^{+}\right]=2.56 \times 10^{-3} \mathrm{Mand}\left[\mathrm{Cu}^{2+}\right]=8.25 \times 10^{-4} \mathrm{M}$

David Collins

Numerade Educator

Problem 93

Using the appropriate standard potentials in Appendix 6, determine the equilibrium constant for the following reaction at $298 \mathrm{K}$
$$\mathrm{Fe}^{3+}(a q)+\mathrm{Cr}^{2+}(a q) \rightarrow \mathrm{Fe}^{2+}(a q)+\mathrm{Cr}^{3+}(a q)$$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 94

Using the appropriate standard potentials in Appendix 6, determine the equilibrium constant at $298 \mathrm{K}$ for the following reaction between $\mathrm{MnO}_{2}$ and $\mathrm{Fe}^{2+}$ in acid solution:
$4 \mathrm{H}^{+}(a q)+\mathrm{MnO}_{2}(s)+2 \mathrm{Fe}^{2+}(a q) \rightarrow$
$$\mathrm{Mn}^{2+}(a q)+2 \mathrm{Fe}^{3+}(a q)+2 \mathrm{H}_{2} \mathrm{O}(\ell)$$

David Collins

Numerade Educator

Problem 95

Electrolysis of Seawater Magnesium metal is obtained by the electrolysis of molten $\mathrm{Mg}^{2+}$ salts from evaporated seawater.
a. Would elemental Mg form at the cathode or anode?
b. Do you think the principal ingredient in sea salt (NaCl) would need to be separated from the $\mathrm{Mg}^{2+}$ salts before electrolysis? Explain your answer.
c. Would electrolysis of an aqueous solution of $\mathrm{Mg} \mathrm{Cl}_{2}$ also produce elemental Mg?
d. If your answer to part (c) was no, what would be the products of electrolysis?

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 96

Silverware Tarnish Low concentrations of hydrogen sulfide in air react with silver to form $\mathrm{Ag}_{2} \mathrm{S}$, more familiar to us as tarnish. Silver polish contains aluminum metal powder in
a basic suspension.
a. Write a balanced net ionic equation for the redox reaction between $\mathrm{Ag}_{2} \mathrm{S}$ and $\mathrm{Al}$ metal that produces $\mathrm{Ag}$ metal and $\mathrm{Al}(\mathrm{OH})_{3}$
b. Calculate $E^{\circ}$ for the reaction.

David Collins

Numerade Educator

Problem 97

A magnesium battery can be constructed from an anode of magnesium metal and a cathode of molybdenum sulfide, $\mathrm{Mo}_{3} \mathrm{S}_{4} .$ The standard reduction potentials of the electrode half-reactions are
$$\mathrm{Mg}^{2+}(a q)+2 \mathrm{e}^{-} \rightarrow \mathrm{Mg}(s) \quad E^{\circ}=-2.37 \mathrm{V}$$
$\mathrm{Mg}^{2+}(a q)+\mathrm{Mo}_{3} \mathrm{S}_{4}(s)+2 \mathrm{e}^{-} \rightarrow \mathrm{MgMo}_{3} \mathrm{S}_{4}(s) \quad E^{\circ}=?$
a. If the standard cell potential for the battery is $1.50 \mathrm{V}$ what is the value of $E^{\circ}$ for the reduction of $\mathrm{Mo}_{3} \mathrm{S}_{4} ?$
b. What are the apparent oxidation states of Mo in $\mathrm{Mo}_{3} \mathrm{S}_{4}$ and in $\mathrm{MgMo}_{3} \mathrm{S}_{4} ?$
"c. The electrolyte in the battery contains a complex magnesium salt, $\mathrm{Mg}\left(\mathrm{AlCl}_{3} \mathrm{CH}_{3}\right)_{2} .$ Why is it necessary to include $\mathrm{Mg}^{2+}$ ions in the electrolyte?

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 98

Suppose there were a scale for expressing electrode potentials in which the standard potential for the reduction of water in base
$$2 \mathrm{H}_{2} \mathrm{O}(\ell)+2 \mathrm{c}^{-} \rightarrow \mathrm{H}_{2}(g)+2 \mathrm{OH}^{-}(a q)$$
is assigned an $E^{\circ}$ value of $0.000 \mathrm{V}$. How would the standard potential values on this new scale differ from those in Appendix $6 ?$

David Collins

Numerade Educator

Problem 99

Clinical Chemistry The concentration of $\mathrm{Na}^{+}$ ions in $\mathrm{red}$ blood cells $(11 \mathrm{m} M)$ and in the surrounding plasma (140 $\mathrm{m} M$ are quite different. Calculate the potential difference across the cell membrane as a result of this concentration gradient at $37^{\circ} \mathrm{C}$

Morgan Sizemore

Morgan Sizemore

Numerade Educator

Problem 100

Waterline Corrosion The photo in Figure $\mathrm{P} 18.100$ shows a phenomenon known as waterline corrosion. Assuming the oxidizing agent in the corrosion process is $\mathrm{O}_{2},$ propose a reason why metal pilings such as this one tend to corrode the most at the waterline and corrode less at heights above and below the waterline.
PICTURE CANT COPY

David Collins

Numerade Educator