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Chemistry

Raymond Chang, Jason Overby

Chapter 18

Electrochemistry - all with Video Answers

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Chapter Questions

08:01

Problem 1

Balance the following redox equations by the ionelectron method:
(a) $\mathrm{H}_{2} \mathrm{O}_{2}+\mathrm{Fe}^{2+} \longrightarrow \mathrm{Fe}^{3+}+\mathrm{H}_{2} \mathrm{O}$ (in acidic
solution)
(b) $\mathrm{Cu}+\mathrm{HNO}_{3} \longrightarrow \mathrm{Cu}^{2+}+\mathrm{NO}+\mathrm{H}_{2} \mathrm{O}$ (in acidic
solution)
(c) $\mathrm{CN}^{-}+\mathrm{MnO}_{4}^{-} \longrightarrow \mathrm{CNO}^{-}+\mathrm{MnO}_{2}$ (in basic
solution)
(d) $\mathrm{Br}_{2} \longrightarrow \mathrm{BrO}_{3}^{-}+\mathrm{Br}^{-}$ (in basic solution)
(e) $\mathrm{S}_{2} \mathrm{O}_{3}^{2-}+\mathrm{I}_{2} \longrightarrow \mathrm{I}^{-}+\mathrm{S}_{4} \mathrm{O}_{6}^{2-}$ (in acidic solution)

Shazia Naz
Shazia Naz
Numerade Educator
05:34

Problem 2

Balance the following redox equations by the ionelectron method:
(a) $\mathrm{Mn}^{2+}+\mathrm{H}_{2} \mathrm{O}_{2} \longrightarrow \mathrm{MnO}_{2}+\mathrm{H}_{2} \mathrm{O}$ (in basic
solution)
(b) $\mathrm{Bi}(\mathrm{OH})_{3}+\mathrm{SnO}_{2}^{2-} \longrightarrow \mathrm{SnO}_{3}^{2-}+\mathrm{Bi}$ (in basic
solution)
(c) $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+\mathrm{C}_{2} \mathrm{O}_{4}^{2-} \longrightarrow \mathrm{Cr}^{3+}+\mathrm{CO}_{2}$ (in
acidic solution)
(d) $\mathrm{ClO}_{3}^{-}+\mathrm{Cl}^{-} \longrightarrow \mathrm{Cl}_{2}+\mathrm{ClO}_{2}$ (in acidic solution)

Shazia Naz
Shazia Naz
Numerade Educator
05:35

Problem 3

Define the following terms: anode, cathode, cell voltage, electromotive force, and standard reduction potential.

Anatole Borisov
Anatole Borisov
Numerade Educator
03:17

Problem 4

Describe the basic features of a galvanic cell. Why are the two components of the cell separated from each other?

Anatole Borisov
Anatole Borisov
Numerade Educator
02:22

Problem 5

What is the function of a salt bridge? What kind of electrolyte should be used in a salt bridge?

Anatole Borisov
Anatole Borisov
Numerade Educator
02:02

Problem 6

What is a cell diagram? Write the cell diagram for a galvanic cell consisting of an $\mathrm{Al}$ electrode placed in a $1 M$ Al(NO $_{3}$ ) $_{3}$ solution and a Ag electrode placed in a $1 M \mathrm{AgNO}_{3}$ solution.

Shazia Naz
Shazia Naz
Numerade Educator
05:27

Problem 7

What is the difference between the half-reactions discussed in redox processes in Chapter 4 and the half-cell reactions discussed in Section $18.2 ?$

Shazia Naz
Shazia Naz
Numerade Educator
01:03

Problem 8

Define the following terms: electromotive force and standard reduction potential.

David Collins
David Collins
Numerade Educator
01:08

Problem 9

Use the information in Table $2.1,$ and calculate the Faraday constant.

David Collins
David Collins
Numerade Educator
03:58

Problem 10

Discuss the spontaneity of an electrochemical reaction in terms of its standard emf $\left(E_{\text {cell }}^{\circ}\right)$.

Vishal Sharma
Vishal Sharma
Numerade Educator
View

Problem 11

Calculate the standard emf of a cell that uses the $\mathrm{Mg} / \mathrm{Mg}^{2+}$ and $\mathrm{Cu} / \mathrm{Cu}^{2+}$ half-cell reactions at $25^{\circ} \mathrm{C}$ Write the equation for the cell reaction that occurs under standard-state conditions.

Ronald Prasad
Ronald Prasad
Numerade Educator
02:28

Problem 12

Calculate the standard emf of a cell that uses Ag/Ag $^{+}$ and $\mathrm{Al} / \mathrm{Al}^{3+}$ half-cell reactions. Write the cell reaction that occurs under standard-state conditions.

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
01:36

Problem 13

Predict whether $\mathrm{Fe}^{3+}$ can oxidize $\mathrm{I}^{-}$ to $\mathrm{I}_{2}$ under standard-state conditions.

Anatole Borisov
Anatole Borisov
Numerade Educator
04:04

Problem 14

Which of the following reagents can oxidize $\mathrm{H}_{2} \mathrm{O}$ to $\mathrm{O}_{2}(g)$ under standard-state conditions: $\mathrm{H}^{+}(a q), \mathrm{Cl}^{-}(a q)$ $\mathrm{Cl}_{2}(g), \mathrm{Cu}^{2+}(a q), \mathrm{Pb}^{2+}(a q), \mathrm{MnO}_{4}^{-}(a q)$ (in acid)?

Anatole Borisov
Anatole Borisov
Numerade Educator
01:04

Problem 15

Consider the following half-reactions:
$$\mathrm{MnO}_{4}^{-}(a q)+8 \mathrm{H}^{+}(a q)+5 e^{-} \overrightarrow{\mathrm{Mn}^{2+}}(a q)+4 \mathrm{H}_{2} \mathrm{O}(l)$$
$$\mathrm{NO}_{3}^{-}(a q)+4 \mathrm{H}^{+}(a q)+3 e^{-} \longrightarrow_{\mathrm{NO}(g)+2 \mathrm{H}_{2} \mathrm{O}(l)}$$

Nicole Krahulik
Nicole Krahulik
Numerade Educator
04:48

Problem 16

Predict whether the following reactions would occur spontaneously in aqueous solution at $25^{\circ} \mathrm{C}$. Assume that the initial concentrations of dissolved species are all $1.0 M$
(a) $\mathrm{Ca}(s)+\mathrm{Cd}^{2+}(a q) \longrightarrow \mathrm{Ca}^{2+}(a q)+\mathrm{Cd}(s)$
(b) $2 \mathrm{Br}^{-}(a q)+\mathrm{Sn}^{2+}(a q) \longrightarrow \mathrm{Br}_{2}(l)+\operatorname{Sn}(s)$
(c) $2 \mathrm{Ag}(s)+\mathrm{Ni}^{2+}(a q) \longrightarrow 2 \mathrm{Ag}^{+}(a q)+\mathrm{Ni}(s)$
(d) $\mathrm{Cu}^{+}(a q)+\mathrm{Fe}^{3+}(a q) \longrightarrow$ $$\mathrm{Cu}^{2+}(a q)+\mathrm{Fe}^{2+}(a q)$$

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
00:41

Problem 17

Which species in each pair is a better oxidizing agent under standard-state conditions:
(a) $\mathrm{Br}_{2}$ or $\mathrm{Au}^{3+} ?$
(b) $\mathrm{H}_{2}$ or $\mathrm{Ag}^{+} ?$
(c) $\mathrm{Cd}^{2+}$ or $\mathrm{Cr}^{3+} ?$
(d) $\mathrm{O}_{2}$ in acidic media or $\mathrm{O}_{2}$ in basic media?

Shazia Naz
Shazia Naz
Numerade Educator
01:07

Problem 18

Which species in each pair is a better reducing agent under standard-state conditions:
(a) Na or Li?
(b) $\mathrm{H}_{2}$ or $\mathrm{I}_{2} ?(\mathrm{c}) \mathrm{Fe}^{2+}$ or $\mathrm{Ag} ?$
(d) $\mathrm{Br}^{-}$ or $\mathrm{Co}^{2+} ?$

Shazia Naz
Shazia Naz
Numerade Educator
01:22

Problem 19

Consider the electrochemical reaction $\mathrm{Sn}^{2+}+\mathrm{X} \longrightarrow$ $\mathrm{Sn}+\mathrm{X}^{2+}$. Given that $E_{\text {cell }}^{\circ}=0.14 \mathrm{~V},$ what is the $E^{\circ}$ for the $\mathrm{X}^{2+} / \mathrm{X}$ half-reaction?

David Collins
David Collins
Numerade Educator
00:58

Problem 20

The $E_{\text {cell }}^{\circ}$ for the following cell is $1.54 \mathrm{~V}$ at $25^{\circ} \mathrm{C}$ : $$\mathrm{U}(s) \mid \mathrm{U}^{3+}(a q)\left\|\mathrm{Ni}^{2+}(a q)\right\| \mathrm{Ni}(s)$$
Calculate the standard reduction potential for the $\mathrm{U}^{3+} / \mathrm{U}$ half-cell.

Shazia Naz
Shazia Naz
Numerade Educator
03:42

Problem 21

Write the equations relating $\Delta G^{\circ}$ and $K$ to the standard emf of a cell. Define all the terms.

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
View

Problem 22

The $E^{\circ}$ value of one cell reaction is positive and that of another cell reaction is negative. Which cell reaction will proceed toward the formation of more products at equilibrium?

Shazia Naz
Shazia Naz
Numerade Educator
00:03

Problem 23

What is the equilibrium constant for the following reaction at $25^{\circ} \mathrm{C} ?$
$$\mathrm{Mg}(s)+\mathrm{Zn}^{2+}(a q) \rightleftharpoons \mathrm{Mg}^{2+}(a q)+\mathrm{Zn}(s)$$

Dr. Satish Ingale
Dr. Satish Ingale
Numerade Educator
01:58

Problem 24

The equilibrium constant for the reaction
$$\operatorname{Sr}(s)+\operatorname{Mg}^{2+}(a q) \rightleftharpoons \operatorname{Sr}^{2+}(a q)+\operatorname{Mg}(s)$$ is $2.69 \times 10^{12}$ at $25^{\circ} \mathrm{C}$. Calculate $E^{\circ}$ for a cell made up of $\mathrm{Sr} / \mathrm{Sr}^{2+}$ and $\mathrm{Mg} / \mathrm{Mg}^{2+}$ half-cells.

Shazia Naz
Shazia Naz
Numerade Educator
01:04

Problem 25

Use the standard reduction potentials to find the equilibrium constant for each of the following reactions at $25^{\circ} \mathrm{C}$
(a) $\mathrm{Br}_{2}(I)+2 \mathrm{I}^{-}(a q) \rightleftharpoons 2 \mathrm{Br}^{-}(a q)+\mathrm{I}_{2}(s)$
(b) $2 \mathrm{Ce}^{4+}(a q)+2 \mathrm{Cl}^{-}(a q) \rightleftharpoons \mathrm{Cl}_{2}(g)+2 \mathrm{Ce}^{3+}(a q)$
(c) $\begin{aligned} 5 \mathrm{Fe}^{2+}(a q)+\mathrm{MnO}_{4}^{-}(a q)+8 \mathrm{H}^{+}(a q) & \Longrightarrow \\ \mathrm{Mn}^{2+}(a q)+4 \mathrm{H}_{2} \mathrm{O}(l)+5 \mathrm{Fe}^{3+}(a q) \end{aligned}$

Kratika Bhadauria
Kratika Bhadauria
Numerade Educator
02:08

Problem 26

Calculate $\Delta G^{\circ}$ and $K_{c}$ for the following reactions at $25^{\circ} \mathrm{C}$
(a) $\mathrm{Mg}(s)+\mathrm{Pb}^{2+}(a q) \Longrightarrow \mathrm{Mg}^{2+}(a q)+\mathrm{Pb}(s)$
(b) $\mathrm{Br}_{2}(l)+2 \mathrm{I}^{-}(a q) \Longrightarrow 2 \mathrm{Br}^{-}(a q)+\mathrm{I}_{2}(s)$
(c) $\mathrm{O}_{2}(g)+4 \mathrm{H}^{+}(a q)+4 \mathrm{Fe}^{2+}(a q) \Longrightarrow$ $2 \mathrm{H}_{2} \mathrm{O}(l)+4 \mathrm{Fe}^{3+}(a q)$
(d) $2 \mathrm{Al}(s)+3 \mathrm{I}_{2}(s) \Longrightarrow 2 \mathrm{Al}^{3+}(a q)+6 \mathrm{I}^{-}(a q)$

Manik Pulyani
Manik Pulyani
Numerade Educator
04:59

Problem 27

Under standard-state conditions, what spontaneous reaction will occur in aqueous solution among the ions $\mathrm{Ce}^{4+}, \mathrm{Ce}^{3+}, \mathrm{Fe}^{3+},$ and $\mathrm{Fe}^{2+} ?$ Calculate $\Delta G^{\circ}$ and
$K_{\mathrm{c}}$ for the reaction.

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
03:21

Problem 28

Given that $E^{\circ}=0.52 \mathrm{~V}$ for the reduction $\mathrm{Cu}^{+}(a q)+$ $e^{-} \longrightarrow \mathrm{Cu}(s),$ calculate $E^{\circ}, \Delta G^{\circ},$ and $K$ for the following reaction at $25^{\circ} \mathrm{C}$ :
$$2 \mathrm{Cu}^{+}(a q) \longrightarrow \mathrm{Cu}^{2+}(a q)+\mathrm{Cu}(s)$$

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
03:52

Problem 29

Write the Nernst equation and explain all the terms.

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
06:01

Problem 30

Write the Nernst equation for the following processes at some temperature $T$.
(a) $\mathrm{Mg}(s)+\mathrm{Sn}^{2+}(a q) \longrightarrow \mathrm{Mg}^{2+}(a q)+\operatorname{Sn}(s)$
(b) $2 \mathrm{Cr}(s)+3 \mathrm{~Pb}^{2+}(a q) \longrightarrow 2 \mathrm{Cr}^{3+}(a q)+3 \mathrm{~Pb}(s)$

Anatole Borisov
Anatole Borisov
Numerade Educator
03:12

Problem 31

What is the potential of a cell made up of $\mathrm{Zn} / \mathrm{Zn}^{2+}$ and $\mathrm{Cu} / \mathrm{Cu}^{2+}$ half-cells at $25^{\circ} \mathrm{C}$ if $\left[\mathrm{Zn}^{2+}\right]=0.25 \mathrm{M}$ and
$\left[\mathrm{Cu}^{2+}\right]=0.15 \mathrm{M} ?$

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
03:29

Problem 32

Calculate $E^{\circ}, E,$ and $\Delta G$ for the following cell meactions
(a) $\mathrm{Mg}(s)+\mathrm{Sn}^{2+}(a q) \longrightarrow \mathrm{Mg}^{2+}(a q)+\mathrm{Sn}(s)$ $\left[\mathrm{Mg}^{2+}\right]=0.045 M,\left[\mathrm{Sn}^{2+}\right]=0.035 M$
(b) $3 \mathrm{Zn}(s)+2 \mathrm{Cr}^{3+}(a q) \longrightarrow 3 \mathrm{Zn}^{2+}(a q)+2 \mathrm{Cr}(s)$
$\left[\mathrm{Cr}^{3+}\right]=0.010 \mathrm{M},\left[\mathrm{Zn}^{2+}\right]=0.0085 \mathrm{M}$

David Collins
David Collins
Numerade Educator
04:28

Problem 33

Calculate the standard potential of the cell consisting of the $\mathrm{Zn} / \mathrm{Zn}^{2+}$ half-cell and the $\mathrm{SHE}$. What will the emf of the cell be if $\left[\mathrm{Zn}^{2+}\right]=0.45 \mathrm{M}, \mathrm{P}_{\mathrm{H}_{2}}=$
$2.0 \mathrm{~atm},$ and $\left[\mathrm{H}^{+}\right]=1.8 \mathrm{M} ?$

Shazia Naz
Shazia Naz
Numerade Educator
02:04

Problem 34

What is the emf of a cell consisting of a $\mathrm{Pb}^{2+} / \mathrm{Pb}$ half-cell and a $\mathrm{Pt} / \mathrm{H}^{+} / \mathrm{H}_{2}$ half-cell if $\left[\mathrm{Pb}^{2+}\right]=0.10 \mathrm{M}$, $\left[\mathrm{H}^{+}\right]=0.050 \mathrm{M},$ and $P_{\mathrm{H}}=2.0 \mathrm{~atm} ?$

David Collins
David Collins
Numerade Educator
02:42

Problem 35

Referring to the arrangement in Figure $18.1,$ calculate the $\left[\mathrm{Cu}^{2+}\right] /\left[\mathrm{Zn}^{2+}\right]$ ratio at which the following reaction is spontaneous at $25^{\circ} \mathrm{C}$
$\mathrm{Cu}(s)+\mathrm{Zn}^{2+}(a q) \longrightarrow \mathrm{Cu}^{2+}(a q)+\mathrm{Zn}(s)$

David Collins
David Collins
Numerade Educator
03:57

Problem 36

Calculate the emf of the following concentration cell.
$\mathrm{Mg}(s) \mid \mathrm{Mg}^{2+}(0.24 M) \| \mathrm{Mg}^{2+}(0.53 \mathrm{M}) \mathrm{IMg}(s)$

Nicholas Mogoi
Nicholas Mogoi
Numerade Educator
02:54

Problem 37

Explain the differences between a primary galvanic cell-one that is not rechargeable-and a storage cell (for example, the lead storage battery), which is rechargeable.

Shazia Naz
Shazia Naz
Numerade Educator
05:14

Problem 38

Discuss the advantages and disadvantages of fuel cells over conventional power plants in producing electricity.

Shazia Naz
Shazia Naz
Numerade Educator
06:07

Problem 39

The hydrogen-oxygen fuel cell is described in Section 18.6 . (a) What volume of $\mathrm{H}_{2}(g),$ stored at $25^{\circ} \mathrm{C}$ at a pressure of 155 atm, would be needed to run an electric motor drawing a current of $8.5 \mathrm{~A}$ for $3.0 \mathrm{~h} ?$ (b) What volume (liters) of air at $25^{\circ} \mathrm{C}$ and 1.00 atm will have to pass into the cell per minute to run the motor? Assume that air is 20 percent $\mathrm{O}_{2}$ by volume and that all the $\mathrm{O}_{2}$ is consumed in the cell. The other components of air do not affect the fuel-cell reactions. Assume ideal gas behavior.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
01:39

Problem 40

Calculate the standard emf of the propane fuel cell discussed in Section 18.6 at $25^{\circ} \mathrm{C},$ given that $\Delta G_{\mathrm{f}}^{\circ}$ for propane is $-23.5 \mathrm{~kJ} / \mathrm{mol}$.

Nicholas Mogoi
Nicholas Mogoi
Numerade Educator
04:51

Problem 41

Steel hardware, including nuts and bolts, is often coated with a thin plating of cadmium. Explain the function of the cadmium layer.

Shazia Naz
Shazia Naz
Numerade Educator
01:54

Problem 42

"Galvanized iron" is steel sheet that has been coated with zinc; "tin" cans are made of steel sheet coated with tin. Discuss the functions of these coatings and

Nicholas Mogoi
Nicholas Mogoi
Numerade Educator
08:22

Problem 42

Galvanized iron" is steel sheet that has been coated with zinc; "tin" cans are made of steel sheet coated with tin. Discuss the functions of these coatings and the electrochemistry of the corrosion reactions that occur if an electrolyte contacts the scratched surface of a galvanized iron sheet or a tin can.

Shazia Naz
Shazia Naz
Numerade Educator
03:33

Problem 43

Tarnished silver contains $\mathrm{Ag}_{2} \mathrm{~S}$. The tarnish can be removed by placing silverware in an aluminum pan containing an inert electrolyte solution, such as $\mathrm{NaCl} .$ Explain the electrochemical principle for this procedure. [The standard reduction potential for the half-cell reaction $\mathrm{Ag}_{2} \mathrm{~S}(s)+2 e^{-} \longrightarrow 2 \mathrm{Ag}(s)+$
$\mathrm{S}^{2-}(a q)$ is $-0.71 \mathrm{~V} .1$

Anatole Borisov
Anatole Borisov
Numerade Educator
02:11

Problem 44

How does the tendency of iron to rust depend on the $\mathrm{pH}$ of solution?

Shazia Naz
Shazia Naz
Numerade Educator
02:04

Problem 45

What is the difference between a galvanic cell (such as a Daniell cell) and an electrolytic cell?

Anatole Borisov
Anatole Borisov
Numerade Educator
01:02

Problem 46

Describe the electrolysis of an aqueous solution of $\mathrm{KNO}_{3}$

Shazia Naz
Shazia Naz
Numerade Educator
01:39

Problem 47

The half-reaction at an electrode is $$\mathrm{Mg}^{2+}(\text { molten })+2 e^{-} \longrightarrow \mathrm{Mg}(s)$$
Calculate the number of grams of magnesium that can be produced by supplying $1.00 \mathrm{~F}$ to the electrode.

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
02:42

Problem 48

Consider the electrolysis of molten barium chloride, $\mathrm{BaCl}_{2}$. (a) Write the half-reactions. (b) How many grams of barium metal can be produced by supplying 0.50 A for 30 min?

Shazia Naz
Shazia Naz
Numerade Educator
02:28

Problem 49

Considering only the cost of electricity, would it be cheaper to produce a ton of sodium or a ton of aluminum by electrolysis?

Shazia Naz
Shazia Naz
Numerade Educator
00:36

Problem 50

If the cost of electricity to produce magnesium by the electrolysis of molten magnesium chloride is $\$ 155$ per ton of metal, what is the cost (in dollars) of the electricity necessary to produce
(a) 10.0 tons of aluminum,
(b) 30.0 tons of sodium,
(c) 50.0 tons of calcium?

Shazia Naz
Shazia Naz
Numerade Educator
04:12

Problem 51

One of the half-reactions for the electrolysis of water is $$2 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{O}_{2}(g)+4 \mathrm{H}^{+}(a q)+4 e^{-}$$
If $0.076 \mathrm{~L}$ of $\mathrm{O}_{2}$ is collected at $25^{\circ} \mathrm{C}$ and $755 \mathrm{mmH} \mathrm{g}$. how many moles of electrons had to pass through the solution?

Rashmi Sinha
Rashmi Sinha
Numerade Educator
10:51

Problem 52

How many moles of electrons are required to produce (a) $0.84 \mathrm{~L}$ of $\mathrm{O}_{2}$ at exactly 1 atm and $25^{\circ} \mathrm{C}$ from aqueous $\mathrm{H}_{2} \mathrm{SO}_{4}$ solution;
(b) $1.50 \mathrm{~L}$ of $\mathrm{Cl}_{2}$ at $750 \mathrm{mmHg}$ and $20^{\circ} \mathrm{C}$ from molten $\mathrm{NaCl} ;$ (c) $6.0 \mathrm{~g}$ of Sn from molten $\mathrm{SnCl}_{2} ?$

Rashmi Sinha
Rashmi Sinha
Numerade Educator
02:03

Problem 53

Calculate the amounts of $\mathrm{Cu}$ and $\mathrm{Br}_{2}$ produced in $1.0 \mathrm{~h}$ at inert electrodes in a solution of $\mathrm{CuBr}_{2}$ by a current of $4.50 \mathrm{~A}$.

Shazia Naz
Shazia Naz
Numerade Educator
02:03

Problem 54

Calculate the amounts of $\mathrm{Cu}$ and $\mathrm{Br}_{2}$ produced in $1.0 \mathrm{~h}$ at inert electrodes in a solution of $\mathrm{CuBr}_{2}$ by a current of 4.50 A.

Shazia Naz
Shazia Naz
Numerade Educator
00:57

Problem 54

In the electrolysis of an aqueous AgNO $_{3}$ solution, $0.67 \mathrm{~g}$ of $\mathrm{Ag}$ is deposited after a certain period of time. (a) Write the half-reaction for the reduction of $\mathrm{Ag}^{+} .$ (b) What is the probable oxidation halfreaction? (c) Calculate the quantity of electricity used, in coulombs.

Manik Pulyani
Manik Pulyani
Numerade Educator
01:03

Problem 55

A steady current was passed through molten $\mathrm{CoSO}_{4}$ until $2.35 \mathrm{~g}$ of metallic cobalt was produced. Calculate the number of coulombs of electricity used.

Ronald Prasad
Ronald Prasad
Numerade Educator
04:40

Problem 56

A constant electric current flows for $3.75 \mathrm{~h}$ through two electrolytic cells connected in series. One contains a solution of $\mathrm{AgNO}_{3}$ and the second a solution of $\mathrm{CuCl}_{2}$. During this time $2.00 \mathrm{~g}$ of silver are deposited in the first cell. (a) How many grams of copper are deposited in the second cell? (b) What is the current flowing, in amperes?

Shazia Naz
Shazia Naz
Numerade Educator
02:50

Problem 57

What is the hourly production rate of chlorine gas (in $\mathrm{kg}$ ) from an electrolytic cell using aqueous $\mathrm{NaCl}$ electrolyte and carrying a current of $1.500 \times 10^{3} \mathrm{~A} ?$ The anode efficiency for the oxidation of $\mathrm{Cl}^{-}$ is 93.0 percent.

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
03:31

Problem 58

Chromium plating is applied by electrolysis to objects suspended in a dichromate solution, according to the following (unbalanced) half-reaction: $$\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+e^{-}+\mathrm{H}^{+}(a q) \longrightarrow \mathrm{Cr}(s)+\mathrm{H}_{2} \mathrm{O}(l) $$
How long (in hours) would it take to apply a chromium plating $1.0 \times 10^{-2} \mathrm{~mm}$ thick to a car bumper with a surface area of $0.25 \mathrm{~m}^{2}$ in an electrolytic cell carrying a current of 25.0 A? (The density of chro$\left.\operatorname{mium}_{\text {is }} 7.19 \mathrm{~g} / \mathrm{cm}^{3} .\right)$

David Collins
David Collins
Numerade Educator
02:50

Problem 59

The passage of a current of 0.750 A for $25.0 \mathrm{~min}$ deposited $0.369 \mathrm{~g}$ of copper from a $\mathrm{CuSO}_{4}$ solution. From this information, calculate the molar mass of copper.

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
01:38

Problem 60

A quantity of $0.300 \mathrm{~g}$ of copper was deposited from a CuSO solution by passing a current of 3.00 A through the solution for 304 s. Calculate the value of the Faraday constant.

Nicholas Mogoi
Nicholas Mogoi
Numerade Educator
02:30

Problem 61

In a certain electrolysis experiment, $1.44 \mathrm{~g}$ of $\mathrm{Ag}$ were deposited in one cell (containing an aqueous AgNO solution), while $0.120 \mathrm{~g}$ of an unknown metal X was deposited in another cell (containing an aqueous $\mathrm{XCl}_{3}$ solution in series with the $\mathrm{AgNO}_{3}$ cell. Calculate the molar mass of X.

Nicholas Mogoi
Nicholas Mogoi
Numerade Educator
03:28

Problem 62

One of the half-reactions for the electrolysis of water is $$2 \mathrm{H}^{+}(a q)+2 e^{-} \longrightarrow \mathrm{H}_{2}(g)$$
If $0.845 \mathrm{~L}$ of $\mathrm{H}_{2}$ is collected at $25^{\circ} \mathrm{C}$ and $782 \mathrm{mmHg}$, how many moles of electrons had to pass through the solution?

Rashmi Sinha
Rashmi Sinha
Numerade Educator
02:49

Problem 63

A steady current of 10.0 A is passed through three electrolytic cells for $10.0 \mathrm{~min} .$ Calculate the mass of the metals formed if the solutions are $0.10 M \mathrm{AgNO}_{3}, 0.10 M \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2},$ and $0.10 M$
$\mathrm{Au}\left(\mathrm{NO}_{3}\right)_{3}$

David Collins
David Collins
Numerade Educator
02:55

Problem 64

Industrially, copper metal can be purified electrolytically according to the following arrangement.

David Collins
David Collins
Numerade Educator
02:25

Problem 64

Industrially, copper metal can be purified electrolytically according to the following arrangement. The anode is made of the impure Cu electrode and the cathode is the pure Cu electrode. The electrodes are immersed in a $\mathrm{CuSO}_{4}$ solution.
(a) Write the half-cell reactions at the electrodes. (b) Calculate the mass (in grams) of Cu purified after passing a current of 20 A for $10 \mathrm{~h}$. (c) Explain why impurities such as $\mathrm{Zn}, \mathrm{Fe}, \mathrm{Au},$ and $\mathrm{Ag}$ are not deposited at the electrodes.

David Collins
David Collins
Numerade Educator
04:19

Problem 65

A Daniell cell consists of a zinc electrode in $1.00 \mathrm{~L}$ of $1.00 \mathrm{M} \mathrm{ZnSO}_{4}$ and a Cu electrode in $1.00 \mathrm{~L}$ of $1.00 \mathrm{M} \mathrm{CuSO}_{4}$ at $25^{\circ} \mathrm{C}$. A steady current of $10.0 \mathrm{~A}$
is drawn from the cell. Calculate the $E_{\text {cell }}$ after $1.00 \mathrm{~h}$. Assume volumes to remain constant.

David Collins
David Collins
Numerade Educator
04:59

Problem 66

A concentration cell is constructed having Cu electrodes in two CuSO $_{4}$ solutions $\mathrm{A}$ and $\mathrm{B}$. At $25^{\circ} \mathrm{C}$, the osmotic pressures of the two solutions are 48.9 atm and 4.89 atm, respectively. Calculate the $E_{\text {cell }},$ assuming no ion-pair formation.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
07:22

Problem 67

For each of the following redox reactions, (i) write the half-reactions, (ii) write a balanced equation for the whole reaction, (iii) determine in which direction the reaction will proceed spontaneously under standard-state conditions:
(a) $\mathrm{H}_{2}(g)+\mathrm{Ni}^{2+}(a q) \longrightarrow \mathrm{H}^{+}(a q)+\mathrm{Ni}(s)$
(b) $\mathrm{MnO}_{4}^{-}(a q)+\mathrm{Cl}^{-}(a q) \longrightarrow$
$\quad \mathrm{Mn}^{2+}(a q)+\mathrm{Cl}_{2}(g)$ (in acid solution)
$\begin{array}{ll}\text { (c) } \mathrm{Cr}(s)+\mathrm{Zn}^{2+}(a q) & \longrightarrow \mathrm{Cr}^{3+}(a q)+\mathrm{Zn}(s)\end{array}$

Rashmi Sinha
Rashmi Sinha
Numerade Educator
05:36

Problem 68

The oxidation of $25.0 \mathrm{~mL}$ of a solution containing $\mathrm{Fe}^{2+}$ requires $26.0 \mathrm{~mL}$ of $0.0250 \mathrm{M} \mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$ in acidic solution. Balance the following equation and calculate the molar concentration of $\mathrm{Fe}^{2+}$ $\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+\mathrm{Fe}^{2+}+\mathrm{H}^{+} \longrightarrow \mathrm{Cr}^{3+}+\mathrm{Fe}^{3+}$

Shazia Naz
Shazia Naz
Numerade Educator
View

Problem 69

The $\mathrm{SO}_{2}$ present in air is mainly responsible for the phenomenon of acid rain. The concentration of $\mathrm{SO}_{2}$ can be determined by titrating against a standard permanganate solution as follows: $5 \mathrm{SO}_{2}+2 \mathrm{MnO}_{4}^{-}+2 \mathrm{H}_{2} \mathrm{O} \longrightarrow \overrightarrow{5 \mathrm{SO}_{4}^{2-}+2 \mathrm{Mn}^{2+}+4 \mathrm{H}^{+}}$
Calculate the number of grams of $\mathrm{SO}_{2}$ in a sample of air if $7.37 \mathrm{~mL}$ of $0.00800 \mathrm{M} \mathrm{KMnO}_{4}$ solution are required for the titration.

Tom Comey
Tom Comey
Numerade Educator
05:16

Problem 70

A sample of iron ore weighing $0.2792 \mathrm{~g}$ was dissolved in an excess of a dilute acid solution. All the iron was first converted to Fe(II) ions. The solution then required $23.30 \mathrm{~mL}$ of $0.0194 \mathrm{M} \mathrm{KMnO}_{4}$ for oxidation to Fe(III) ions. Calculate the percent by mass of iron in the ore.

Shazia Naz
Shazia Naz
Numerade Educator
04:40

Problem 71

The concentration of a hydrogen peroxide solution can be conveniently determined by titration against a standardized potassium permanganate solution in an acidic medium according to the following unbalanced equation:
$$\mathrm{MnO}_{4}^{-}+\mathrm{H}_{2} \mathrm{O}_{2} \longrightarrow \mathrm{O}_{2}+\mathrm{Mn}^{2+}$$
(a) Balance the above equation. (b) If $36.44 \mathrm{~mL}$ of a $0.01652 M \mathrm{KMnO}_{4}$ solution are required to completely oxidize $25.00 \mathrm{~mL}$ of a $\mathrm{H}_{2} \mathrm{O}_{2}$ solution, calculate the molarity of the $\mathrm{H}_{2} \mathrm{O}_{2}$ solution.

Shazia Naz
Shazia Naz
Numerade Educator
01:31

Problem 72

Oxalic acid $\left(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\right)$ is present in many plants and vegetables. (a) Balance the following equation in acid solution:
$$\mathrm{MnO}_{4}^{-}+\mathrm{C}_{2} \mathrm{O}_{4}^{2-} \longrightarrow \mathrm{Mn}^{2+}+\mathrm{CO}_{2}$$
(b) If a 1.00-g sample of $\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}$ requires $24.0 \mathrm{~mL}$ of $0.0100 \mathrm{M} \mathrm{KMnO}_{4}$ solution to reach the equivalence point, what is the percent by mass of $\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}$ in the sample?

Manik Pulyani
Manik Pulyani
Numerade Educator
01:22

Problem 73

Complete the following table. State whether the cell reaction is spontaneous, nonspontaneous, or at equilibrium.
$=0$

David Collins
David Collins
Numerade Educator
04:45

Problem 74

Calcium oxalate $\left(\mathrm{CaC}_{2} \mathrm{O}_{4}\right)$ is insoluble in water. This property has been used to determine the amount of $\mathrm{Ca}^{2+}$ ions in blood. The calcium oxalate isolated from blood is dissolved in acid and titrated against a standardized $\mathrm{KMnO}_{4}$ solution as described in Problem $18.72 .$ In one test, it is found that the calcium oxalate isolated from a 10.0 -mL sample of blood requires $24.2 \mathrm{~mL}$ of $9.56 \times 10^{-4} \mathrm{M} \mathrm{KMnO}_{4}$ for
titration. Calculate the number of milligrams of calcium per milliliter of blood.

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
02:47

Problem 75

From the following information, calculate the solubility product of AgBr:
$\mathrm{Ag}^{+}(a q)+e^{-} \longrightarrow \operatorname{Ag}(s) \quad E^{\circ}=0.80 \mathrm{~V}$
$\operatorname{AgBr}(s)+e^{-} \longrightarrow \operatorname{Ag}(s)+\operatorname{Br}^{-}(a q) \quad E^{\circ}=0.07 \mathrm{~V}$

David Collins
David Collins
Numerade Educator
04:22

Problem 76

Consider a galvanic cell composed of the SHE and a half-cell using the reaction $\mathrm{Ag}^{+}(a q)+e^{-} \longrightarrow \mathrm{Ag}(s)$
(a) Calculate the standard cell potential. (b) What is the spontaneous cell reaction under standard-state conditions? (c) Calculate the cell potential when $\left[\mathrm{H}^{+}\right]$ in the hydrogen electrode is changed to (i) $1.0 \times 10^{-2} M$ and (ii) $1.0 \times 10^{-5} M$, all other reagents being held at standard-state conditions.
(d) Based on this cell arrangement, suggest a design for a pH meter.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
02:37

Problem 77

A galvanic cell consists of a silver electrode in contact with $346 \mathrm{~mL}$ of $0.100 \mathrm{M} \mathrm{AgNO}_{3}$ solution and a magnesium electrode in contact with $288 \mathrm{~mL}$ of $0.100 M \mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}$ solution. (a) Calculate $E$ for the cell at $25^{\circ} \mathrm{C}$. (b) A current is drawn from the cell until $1.20 \mathrm{~g}$ of silver have been deposited at the silver electrode. Calculate $E$ for the cell at this stage of operation.

Manik Pulyani
Manik Pulyani
Numerade Educator
00:28

Problem 78

Explain why chlorine gas can be prepared by electrolyzing an aqueous solution of $\mathrm{NaCl}$ but fluorine gas cannot be prepared by electrolyzing an aqueous solution of NaF.

Shazia Naz
Shazia Naz
Numerade Educator
03:28

Problem 79

Calculate the emf of the following concentration cell at $25^{\circ} \mathrm{C}$ :
$$\mathrm{Cu}(s)\left|\mathrm{Cu}^{2+}(0.080 M) \| \mathrm{Cu}^{2+}(1.2 M)\right| \mathrm{Cu}(s)$$

Kevin Zaborsky
Kevin Zaborsky
Numerade Educator
04:07

Problem 80

The cathode reaction in the Leclanché cell is given by $$2 \mathrm{MnO}_{2}(s)+\mathrm{Zn}^{2+}(a q)+2 e^{-} \longrightarrow \mathrm{ZnMn}_{2} \mathrm{O}_{4}(s)$$
If a Leclanché cell produces a current of $0.0050 \mathrm{~A}$, calculate how many hours this current supply will last if there are initially $4.0 \mathrm{~g}$ of $\mathrm{MnO}_{2}$ present in the cell. Assume that there is an excess of $\mathrm{Zn}^{2+}$ ions.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
01:30

Problem 81

Suppose you are asked to verify experimentally the electrode reactions shown in Example $18.8 .$ In addition to the apparatus and the solution, you are also given two pieces of litmus paper, one blue and the other red. Describe what steps you would take in this experiment.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
02:54

Problem 82

For a number of years it was not clear whether mercury(I) ions existed in solution as $\mathrm{Hg}^{+}$ or as $\mathrm{Hg}_{2}^{2+}$. To distinguish between these two possibilities, we could set up the following system:
$$\mathrm{Hg}(l) \mid \text { soln } \mathrm{A} \| \operatorname{soln} \mathrm{B} \mid \mathrm{Hg}(l)$$
where soln A contained 0.263 g mercury(I) nitrate per liter and soln $\mathrm{B}$ contained $2.63 \mathrm{~g}$ mercury $(\mathrm{I}) \mathrm{ni}-$ trate per liter. If the measured emf of such a cell is $0.0289 \mathrm{~V}$ at $18^{\circ} \mathrm{C},$ what can you deduce about the nature of the mercury(I) ions?

David Collins
David Collins
Numerade Educator
01:25

Problem 83

An aqueous KI solution to which a few drops of phenolphthalein have been added is electrolyzed using an apparatus like the one shown here: Describe what you would observe at the anode and the cathode. (Hint: Molecular iodine is only slightly soluble in water, but in the presence of $\mathrm{I}^{-}$ ions, it forms the brown color of $\mathrm{I}_{3}^{-}$ ions. See Problem $12.102 .$

Rashmi Sinha
Rashmi Sinha
Numerade Educator
02:37

Problem 84

A piece of magnesium metal weighing $1.56 \mathrm{~g}$ is placed in $100.0 \mathrm{~mL}$ of $0.100 \mathrm{M} \mathrm{AgNO}_{3}$ at $25^{\circ} \mathrm{C}$
Calculate $\left[\mathrm{Mg}^{2+}\right]$ and $\left[\mathrm{Ag}^{+}\right]$ in solution at equilibrium. What is the mass of the magnesium left? The volume remains constant.

Manik Pulyani
Manik Pulyani
Numerade Educator
01:17

Problem 85

Describe an experiment that would enable you to determine which is the cathode and which is the anode in a galvanic cell using copper and zinc electrodes.

Shazia Naz
Shazia Naz
Numerade Educator
04:51

Problem 86

An acidified solution was electrolyzed using copper electrodes. A constant current of 1.18 A caused the anode to lose $0.584 \mathrm{~g}$ after $1.52 \times 10^{3} \mathrm{~s}$. (a) What is the gas produced at the cathode and what is its volume at STP? (b) Given that the charge of an electron is $1.6022 \times 10^{-19} \mathrm{C},$ calculate Avogadro's number. Assume that copper is oxidized to $\mathrm{Cu}^{2+}$ ions.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
04:13

Problem 87

In a certain electrolysis experiment involving $\mathrm{Al}^{3+}$ ions, $60.2 \mathrm{~g}$ of $\mathrm{Al}$ is recovered when a current of $0.352 \mathrm{~A}$ is used. How many minutes did the electrolysis last?

Shazia Naz
Shazia Naz
Numerade Educator
02:47

Problem 88

Consider the oxidation of ammonia: $$4 \mathrm{NH}_{3}(g)+3 \mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{~N}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(l)$$
(a) Calculate the $\Delta G^{\circ}$ for the reaction.
(b) If this reaction were used in a fuel cell, what would the standard cell potential be?

Rashmi Sinha
Rashmi Sinha
Numerade Educator
04:25

Problem 89

When an aqueous solution containing gold(III) salt is electrolyzed, metallic gold is deposited at the cathode and oxygen gas is generated at the anode.
(a) If $9.26 \mathrm{~g}$ of Au is deposited at the cathode, calculate the volume (in liters) of $\mathrm{O}_{2}$ generated at $23^{\circ} \mathrm{C}$ and $747 \mathrm{mmHg} .$
(b) What is the current used if the electrolytic process took $2.00 \mathrm{~h} ?$

Nicole Smina
Nicole Smina
Numerade Educator
02:29

Problem 90

In an electrolysis experiment, a student passes the same quantity of electricity through two electrolytic cells, one containing a silver salt and the other a gold salt. Over a certain period of time, she finds that $2.64 \mathrm{~g}$ of $\mathrm{Ag}$ and $1.61 \mathrm{~g}$ of $\mathrm{Au}$ are deposited at the cathodes. What is the oxidation state of gold in the gold salt?

Rashmi Sinha
Rashmi Sinha
Numerade Educator
01:37

Problem 91

People living in cold-climate countries where there is plenty of snow are advised not to heat their garages in the winter. What is the electrochemical basis for this recommendation?

Shazia Naz
Shazia Naz
Numerade Educator
03:37

Problem 92

Given that $\begin{array}{ll}2 \mathrm{Hg}^{2+}(a q)+2 e^{-} \longrightarrow \mathrm{Hg}_{2}^{2+}(a q) & E^{\circ}=0.92 \mathrm{~V} \\ \mathrm{Hg}_{2}^{2+}(a q)+2 e^{-} \longrightarrow 2 \mathrm{Hg}(l) & E^{\circ}=0.85 \mathrm{~V}\end{array}$ calculate $\Delta G^{\circ}$ and $K$ for the following process at $25^{\circ} \mathrm{C}$ : $\mathrm{Hg}_{2}^{2+}(a q) \longrightarrow \mathrm{Hg}^{2+}(a q)+\mathrm{Hg}(l)$
(The preceding reaction is an example of a disproportionation reaction in which an element in one oxidation state is both oxidized and reduced.)

Rashmi Sinha
Rashmi Sinha
Numerade Educator
05:18

Problem 93

A galvanic cell with $E_{\mathrm{cell}}^{\circ}=0.30 \mathrm{~V}$ can be constructed using an Fe electrode in a $1.0 \mathrm{M} \mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}$ solution, and either a Sn electrode in a $1.0 \mathrm{M} \mathrm{Sn}\left(\mathrm{NO}_{3}\right)_{2}$ solution, or a Cr electrode in a $1.0 \mathrm{M} \mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{3}$ solution, even though $\mathrm{Sn}^{2+} / \mathrm{Sn}$ and $\mathrm{Cr}^{3+} / \mathrm{Cr}$ have different standard reduction potentials. Explain.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
04:23

Problem 94

Shown here is a galvanic cell connected to an electrolytic cell. Label the electrodes (anodes and cathodes) and show the movement of electrons along the wires and cations and anions in solution. For simplicity, the salt bridge is not shown for the galvanic cell.

Shazia Naz
Shazia Naz
Numerade Educator
04:22

Problem 95

Fluorine $\left(\mathrm{F}_{2}\right)$ is obtained by the electrolysis of liquid hydrogen fluoride (HF) containing potassium fluoride (KF). (a) Write the half-cell reactions and the overall reaction for the process. (b) What is the purpose of KF? (c) Calculate the volume of $\mathrm{F}_{2}$ (in liters) collected at $24.0^{\circ} \mathrm{C}$ and 1.2 atm after electrolyzing the solution for $15 \mathrm{~h}$ at a current of 502 A.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
04:03

Problem 96

A 300 -mL solution of $\mathrm{NaCl}$ was electrolyzed for 6.00 min. If the $\mathrm{pH}$ of the final solution was 12.24 calculate the average current used.

Shazia Naz
Shazia Naz
Numerade Educator
02:36

Problem 97

Industrially, copper is purified by electrolysis. The impure copper acts as the anode, and the cathode is made of pure copper. The electrodes are immersed in a CuSO $_{4}$ solution. During electrolysis, copper at the anode enters the solution as $\mathrm{Cu}^{2+}$ while $\mathrm{Cu}^{2+}$ ions are reduced at the cathode. (a) Write halfcell reactions and the overall reaction for the electrolytic process.
(b) Suppose the anode was contaminated with $\mathrm{Zn}$ and $\mathrm{Ag} .$ Explain what happens to these impurities during electrolysis. (c) How many hours will it take to obtain $1.00 \mathrm{~kg}$ of $\mathrm{Cu}$ at a current of $18.9 \mathrm{~A} ?$

David Collins
David Collins
Numerade Educator
02:55

Problem 98

An aqueous solution of a platinum salt is electrolyzed at a current of 2.50 A for $2.00 \mathrm{~h}$. As a result, $9.09 \mathrm{~g}$ of metallic $\mathrm{Pt}$ are formed at the cathode. Calculate the charge on the Pt ions in this solution.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
02:20

Problem 99

Consider a galvanic cell consisting of a magnesium electrode in contact with $1.0 \mathrm{M} \mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}$ and a cadmium electrode in contact with $1.0 \mathrm{M}$ $\mathrm{Cd}\left(\mathrm{NO}_{3}\right)_{2} .$ Calculate $E^{\circ}$ for the cell, and draw a diagram showing the cathode, anode, and direction of electron flow.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
04:52

Problem 100

A current of 6.00 A passes through an electrolytic cell containing dilute sulfuric acid for $3.40 \mathrm{~h}$. If the volume of $\mathrm{O}_{2}$ gas generated at the anode is $4.26 \mathrm{~L}$ (at STP), calculate the charge (in coulombs) on an electron.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
01:45

Problem 101

Gold will not dissolve in either concentrated nitric acid or concentrated hydrochloric acid. However, the metal does dissolve in a mixture of the acids (one part $\mathrm{HNO}_{3}$ and three parts $\mathrm{HCl}$ by volume $)$ called aqua regia. (a) Write a balanced equation for this reaction. (Hint: Among the products are $\mathrm{HAuCl}_{4}$ and $\mathrm{NO}_{2} .$ ) (b) What is the function of $\mathrm{HCl} ?$

Rashmi Sinha
Rashmi Sinha
Numerade Educator
01:18

Problem 102

Explain why most useful galvanic cells give voltages of no more than 1.5 to $2.5 \mathrm{~V}$. What are the prospects for developing practical galvanic cells with voltages of $5 \mathrm{~V}$ or more?

Shazia Naz
Shazia Naz
Numerade Educator
04:42

Problem 103

The table here shows the standard reduction potentials of several half-reactions:
\begin{tabular}{lr}
Half-Reactions & $\boldsymbol{E}^{\circ}(\mathbf{V})$ \\
\hline $\mathrm{A}^{2+}+2 e^{-} \longrightarrow \mathrm{A}$ & -1.46 \\
$\mathrm{~B}_{2}+2 e^{-} \longrightarrow 2 \mathrm{~B}^{-}$ & 0.33 \\
$\mathrm{C}^{3+}+3 e^{-} \longrightarrow \mathrm{C}$ & 1.13 \\
$\mathrm{D}^{+}+e^{-} \longrightarrow \mathrm{D}$ & -0.87 \\
\hline
\end{tabular}

David Collins
David Collins
Numerade Educator
02:58

Problem 104

Consider a concentration cell made of the following two compartments: $\mathrm{Cl}_{2}(0.20 \mathrm{~atm}) \mathrm{ICl}^{-}(1.0 \mathrm{M})$ and
$\mathrm{Cl}_{2}(2.0 \mathrm{~atm}) \mid \mathrm{Cl}^{-}(1.0 \mathrm{M}) .$ Platinum is used as the in-
ert electrodes. Draw a cell diagram for the cell and calculate the emf of the cell at $25^{\circ} \mathrm{C}$.

David Collins
David Collins
Numerade Educator
06:20

Problem 105

A silver rod and a SHE are dipped into a saturated aqueous solution of silver oxalate, $\mathrm{Ag}_{2} \mathrm{C}_{2} \mathrm{O}_{4},$ at $25^{\circ} \mathrm{C}$. The measured potential difference between the rod and the $\mathrm{SHE}$ is $0.589 \mathrm{~V},$ the rod being positive. Calculate the solubility product constant for silver oxalate.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
04:16

Problem 106

Zinc is an amphoteric metal; that is, it reacts with both acids and bases. The standard reduction potential is $-1.36 \mathrm{~V}$ for the reaction
$$
\mathrm{Zn}(\mathrm{OH})_{4}^{2-}(a q)+2 e^{-} \longrightarrow \mathrm{Zn}(s)+4 \mathrm{OH}^{-}(a q)
$$
Calculate the formation constant $\left(K_{f}\right)$ for the reaction
$$
\mathrm{Zn}^{2+}(a q)+4 \mathrm{OH}^{-}(a q) \rightleftharpoons \mathrm{Zn}(\mathrm{OH})_{4}^{2-}(a q)
$$

Rashmi Sinha
Rashmi Sinha
Numerade Educator
02:21

Problem 107

Use the data in Table 18.1 to determine whether or not hydrogen peroxide will undergo disproportionation in an acid medium: $2 \mathrm{H}_{2} \mathrm{O}_{2} \rightarrow 2 \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}$

David Collins
David Collins
Numerade Educator
03:21

Problem 108

The magnitudes (but not the signs) of the standard reduction potentials of two metals $X$ and $Y$ are
$$
\begin{array}{ll}
\mathrm{Y}^{2+}+2 e^{-} \longrightarrow \mathrm{Y} & \mid E^{\mathrm{O}} \mathrm{I}=0.34 \mathrm{~V} \\
\mathrm{X}^{2+}+2 e^{-} \longrightarrow \mathrm{X} & \mid E^{\circ} \mathrm{I}=0.25 \mathrm{~V}
\end{array}
$$ where the II notation denotes that only the magnitude (but not the sign) of the $E^{\circ}$ value is shown. When the half-cells of $\mathrm{X}$ and $\mathrm{Y}$ are connected, electrons flow from $X$ to $Y$. When $X$ is connected to a SHE, electrons flow from $X$ to $\mathrm{SHE}$. (a) Are the $E^{\circ}$ values of the half-reactions positive or negative?
(b) What is the standard emf of a cell made up of $\mathrm{X}$ and $\mathrm{Y} ?$

David Collins
David Collins
Numerade Educator
05:30

Problem 109

A galvanic cell is constructed as follows. One half-cell consists of a platinum wire immersed in a solution containing $1.0 M \mathrm{Sn}^{2+}$ and $1.0 M \mathrm{Sn}^{4+} ;$ the other half-cell has a thallium rod immersed in a solution of $1.0 M \mathrm{Tl}^{+}$. (a) Write the half-cell reactions and the overall reaction.
(b) What is the equilibrium constant at $25^{\circ} \mathrm{C} ?$
(c) What is the cell voltage if the $\mathrm{T} 1^{+}$ concentration is increased tenfold? $\left(E_{\mathrm{TI}^{+} / \mathrm{T} 1}^{\circ}=-0.34 \mathrm{~V} .\right)$

Susan Hallstrom
Susan Hallstrom
Numerade Educator
01:02

Problem 110

Given the standard reduction potential for $\mathrm{Au}^{3+}$ in Table 18.1 and
$$
\mathrm{Au}^{+}(a q)+e^{-} \longrightarrow \mathrm{Au}(s) \quad E^{\circ}=1.69 \mathrm{~V}
$$
answer the following questions. (a) Why does gold not tarnish in air? (b) Will the following disproportionation occur spontaneously?
$$
3 \mathrm{Au}^{+}(a q) \longrightarrow \mathrm{Au}^{3+}(a q)+2 \mathrm{Au}(s)
$$
(c) Predict the reaction between gold and fluorine gas.

Shazia Naz
Shazia Naz
Numerade Educator
02:29

Problem 111

The ingestion of a very small quantity of mercury is not considered too harmful. Would this statement still hold if the gastric juice in your stomach were mostly nitric acid instead of hydrochloric acid?

Shazia Naz
Shazia Naz
Numerade Educator
01:32

Problem 112

When $25.0 \mathrm{~mL}$ of a solution containing both $\mathrm{Fe}^{2+}$ and $\mathrm{Fe}^{3+}$ ions is titrated with $23.0 \mathrm{~mL}$ of $0.0200 \mathrm{M}$ $\mathrm{KMnO}_{4}$ (in dilute sulfuric acid), all of the $\mathrm{Fe}^{2+}$ ions are oxidized to $\mathrm{Fe}^{3+}$ ions. Next, the solution is treated with Zn metal to convert all of the $\mathrm{Fe}^{3+}$ ions to $\mathrm{Fe}^{2+}$ ions. Finally, $40.0 \mathrm{~mL}$ of the same $\mathrm{KMnO}_{4}$ solution are added to the solution in order to oxidize the $\mathrm{Fe}^{2+}$ ions to $\mathrm{Fe}^{3+}$. Calculate the molar concentrations of $\mathrm{Fe}^{2+}$ and $\mathrm{Fe}^{3+}$ in the original solution.

Manik Pulyani
Manik Pulyani
Numerade Educator
01:50

Problem 113

Consider the Daniell cell in Figure $18.1 .$ When viewed externally, the anode appears negative and the cathode positive (electrons are flowing from the anode to the cathode). Yet in solution anions are moving toward the anode, which means that it must appear positive to the anions. Because the anode cannot simultaneously be negative and positive, give an explanation for this apparently contradictory situation.

Shazia Naz
Shazia Naz
Numerade Educator
03:37

Problem 114

Use the data in Table 18.1 to show that the decomposition of $\mathrm{H}_{2} \mathrm{O}_{2}$ (a disproportionation reaction) is spontaneous at $25^{\circ} \mathrm{C}$ :
$$
2 \mathrm{H}_{2} \mathrm{O}_{2}(a q) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{O}_{2}(g)
$$

Rashmi Sinha
Rashmi Sinha
Numerade Educator
02:53

Problem 115

Consider two electrolytic cells A and B. Cell A contains a $0.20 \mathrm{M} \mathrm{CoSO}_{4}$ solution and platinum electrodes. Cell B differs from cell A only in that cobalt metals are used as electrodes. In each case, a current of $0.20 \mathrm{~A}$ is passed through the cell for $1.0 \mathrm{~h}$.
(a) Write equations for the half-cell and overall cell

Susan Hallstrom
Susan Hallstrom
Numerade Educator
10:43

Problem 115

Consider two electrolytic cells A and B. Cell A contains a $0.20 \mathrm{M} \mathrm{CoSO}_{4}$ solution and platinum electrodes. Cell B differs from cell A only in that cobalt metals are used as electrodes. In each case, a current of $0.20 \mathrm{~A}$ is passed through the cell for $1.0 \mathrm{~h}$.
(a) Write equations for the half-cell and overall cell reactions for these cells. (b) Calculate the products formed (in grams) at the anode and cathode in each case.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
00:28

Problem 116

A galvanic cell consists of a Mg electrode in a $1 M$ $\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}$ solution and another metal electrode $\mathrm{X}$ in a $1 M \mathrm{X}\left(\mathrm{NO}_{3}\right)_{2}$ solution. Listed here are the $E_{\mathrm{cell}}^{\circ}$ values of four such galvanic cells. In each case, identify X from Table 18.1 .
(a) $E_{\text {cell }}^{\circ}=2.12 \mathrm{~V}$,
(b) $E_{\text {cell }}^{\circ}=2.24 \mathrm{~V}$
(c) $E_{\text {cell }}^{\circ}=1.61 \mathrm{~V}$
(d) $E_{\text {cell }}^{\circ}=1.93 \mathrm{~V}$.

Shazia Naz
Shazia Naz
Numerade Educator
10:08

Problem 117

The concentration of sulfuric acid in the leadstorage battery of an automobile over a period of time has decreased from 38.0 percent by mass (density = $1.29 \mathrm{~g} / \mathrm{mL})$ to 26.0 percent by mass $(1.19 \mathrm{~g} / \mathrm{mL}) .$
Assume the volume of the acid remains constant at $724 \mathrm{~mL}$. (a) Calculate the total charge in coulombs supplied by the battery. (b) How long (in hours) will it take to recharge the battery back to the original sulfuric acid concentration using a current of 22.4 amperes?

Susan Hallstrom
Susan Hallstrom
Numerade Educator
01:20

Problem 118

Consider a Daniell cell operating under nonstandardstate conditions. Suppose that the cell's reaction is multiplied by $2 .$ What effect does this have on each of the following quantities in the Nernst equation:
(a) $E,(b) E^{\circ},(c) Q$
(d) $\ln Q,$ (e) $n ?$

Shazia Naz
Shazia Naz
Numerade Educator
03:28

Problem 119

An electrolysis cell was constructed similar to the \begin{tabular}{l} one shown in Figure $18.18,$ except $0.1 M$ \\ \hline \end{tabular} $\mathrm{MgCl}_{2}(a q)$ was used as the electrolyte solution. Under these conditions, a clear gas was formed at one electrode and a very pale green gas was formed at the other electrode in roughly equal volumes.
(a) What gases are formed at these electrodes?
(b) Write balanced half-reactions for each electrode. Account for any deviation from the normally expected results.

David Collins
David Collins
Numerade Educator
00:28

Problem 120

Comment on whether $\mathrm{F}_{2}$ will become a stronger oxidizing agent with increasing $\mathrm{H}^{+}$ concentration.

Shazia Naz
Shazia Naz
Numerade Educator
04:17

Problem 121

In recent years there has been much interest in electric cars. List some advantages and disadvantages of electric cars compared to automobiles with internal combustion engines.

Shazia Naz
Shazia Naz
Numerade Educator
01:14

Problem 122

Calculate the pressure of $\mathrm{H}_{2}$ (in atm) required to maintain equilibrium with respect to the following reaction at $25^{\circ} \mathrm{C}$ :
$$
\mathrm{Pb}(s)+2 \mathrm{H}^{+}(a q) \rightleftharpoons \mathrm{Pb}^{2+}(a q)+\mathrm{H}_{2}(g)
$$
Given that $\left[\mathrm{Pb}^{2+}\right]=0.035 M$ and the solution is buffered at $\mathrm{pH} 1.60$.

Manik Pulyani
Manik Pulyani
Numerade Educator
00:57

Problem 123

A piece of magnesium ribbon and a copper wire are partially immersed in a $0.1 M \mathrm{HCl}$ solution in a beaker. The metals are joined externally by another piece of metal wire. Bubbles are seen to evolve at both the $\mathrm{Mg}$ and $\mathrm{Cu}$ surfaces. (a) Write equations representing the reactions occurring at the metals.
(b) What visual evidence would you seek to show that $\mathrm{Cu}$ is not oxidized to $\mathrm{Cu}^{2+} ?$ (c) At some stage, NaOH solution is added to the beaker to neutralize the HCl acid. Upon further addition of $\mathrm{NaOH}$, a white precipitate forms. What is it?

Manik Pulyani
Manik Pulyani
Numerade Educator
02:58

Problem 124

The zinc-air battery shows much promise for electric cars because it is lightweight and rechargeable: The net transformation is $\mathrm{Zn}(s)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{ZnO}(s)$
(a) Write the half-reactions at the zinc-air electrodes and calculate the standard emf of the battery at $25^{\circ} \mathrm{C}$.
(b) Calculate the emf under actual operating conditions when the partial pressure of oxygen is 0.21 atm.
(c) What is the energy density (measured as the energy in kilojoules that can be obtained from $1 \mathrm{~kg}$ of the metal) of the zinc electrode? (d) If a current of $2.1 \times 10^{5} \mathrm{~A}$ is to be drawn from a zinc-air battery system, what volume of air (in liters) would need to be supplied to the battery every second? Assume that the temperature is $25^{\circ} \mathrm{C}$ and the partial pressure of oxygen is 0.21 atm.

Shazia Naz
Shazia Naz
Numerade Educator
01:20

Problem 125

Calculate $E^{\circ}$ for the reactions of mercury with (a) $1 M$ $\mathrm{HCl}$ and $(\mathrm{b}) 1 \mathrm{M} \mathrm{HNO}_{3} . \mathrm{Which}$ acid will oxidize $\mathrm{Hg}$
to $\mathrm{Hg}_{2}^{2+}$ under standard-state conditions? Can you identify which test tube shown contains $\mathrm{HNO}_{3}$ and $\mathrm{Hg}$ and which contains $\mathrm{HCl}$ and $\mathrm{Hg} ?$

Manik Pulyani
Manik Pulyani
Numerade Educator
03:41

Problem 126

Because all alkali metals react with water, it is not possible to measure the standard reduction potentials of these metals directly as in the case of, say, zinc. An indirect method is to consider the following hypothetical reaction
$$
\mathrm{Li}^{+}(a q)+\frac{1}{2} \mathrm{H}_{2}(g) \longrightarrow \mathrm{Li}(s)+\mathrm{H}^{+}(a q)
$$
Using the appropriate equation presented in this chapter and the thermodynamic data in Appendix 2 , calculate $E^{\circ}$ for $\mathrm{Li}^{+}(a q)+e^{-} \longrightarrow \mathrm{Li}(s)$ at $298 \mathrm{~K}$.
Compare your result with that listed in Table 18.1 . (See back endpaper for the Faraday constant.)

Susan Hallstrom
Susan Hallstrom
Numerade Educator
06:38

Problem 127

Because all alkali metals react with water, it is not possible to measure the standard reduction potentials of these metals directly as in the case of, say, zinc. An indirect method is to consider the following hypothetical reaction
$$
\mathrm{Li}^{+}(a q)+\frac{1}{2} \mathrm{H}_{2}(g) \longrightarrow \mathrm{Li}(s)+\mathrm{H}^{+}(a q)
$$
Using the appropriate equation presented in this chapter and the thermodynamic data in Appendix 2 , calculate $E^{\circ}$ for $\mathrm{Li}^{+}(a q)+e^{-} \longrightarrow \mathrm{Li}(s)$ at $298 \mathrm{~K}$.
Compare your result with that listed in Table 18.1 . (See back endpaper for the Faraday constant.)

Susan Hallstrom
Susan Hallstrom
Numerade Educator
01:39

Problem 127

A galvanic cell using $\mathrm{Mg} / \mathrm{Mg}^{2+}$ and $\mathrm{Cu} / \mathrm{Cu}^{2+}$ halfcells operates under standard-state conditions at $25^{\circ} \mathrm{C}$ and each compartment has a volume of $218 \mathrm{~mL}$. The cell delivers 0.22 A for $31.6 \mathrm{~h}$.
(a) How many grams of $\mathrm{Cu}$ are deposited? (b) What is the $\left[\mathrm{Cu}^{2+}\right]$ remaining?

Manik Pulyani
Manik Pulyani
Numerade Educator
01:15

Problem 128

Given the following standard reduction potentials, calculate the ion-product, $K_{w},$ for water at $25^{\circ} \mathrm{C}$ :
$$
\begin{array}{lr}
2 \mathrm{H}^{+}(a q)+2 e^{-} \longrightarrow \mathrm{H}_{2}(g) & E^{\circ}=0.00 \mathrm{~V} \\
2 \mathrm{H}_{2} \mathrm{O}(l)+2 e^{-} \longrightarrow \mathrm{H}_{2}(g)+2 \mathrm{OH}^{-}(a q) & \\
E^{\circ}=-0.83 \mathrm{~V}
\end{array}
$$

Shazia Naz
Shazia Naz
Numerade Educator
11:28

Problem 129

Compare the pros and cons of a fuel cell, such as the hydrogen-oxygen fuel cell, and a coal-fired power station for generating electricity.

Shazia Naz
Shazia Naz
Numerade Educator
06:03

Problem 130

Lead storage batteries are rated by ampere hours, that is, the number of amperes they can deliver in an hour. (a) Show that $1 \mathrm{~A} \cdot \mathrm{h}=3600 \mathrm{C}$. (b) The lead anodes of a certain lead-storage battery have a total mass of 406 g. Calculate the maximum theoretical capacity of the battery in ampere hours. Explain why in practice we can never extract this much energy from the battery. (Hint: Assume all of the lead will be used up in the electrochemical reaction and refer to the electrode reactions in Section $18.6 .$ ) (c) Calculate $E_{\text {cell }}^{\circ}$ and $\Delta G^{\circ}$ for the battery.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
07:59

Problem 131

Use Equations (17.10) and (18.3) to calculate the emf values of the Daniell cell at $25^{\circ} \mathrm{C}$ and $80^{\circ} \mathrm{C}$. Comment on your results. What assumptions are used in the derivation? (Hint: You need the thermodynamic data in Appendix $2 . ?$

Susan Hallstrom
Susan Hallstrom
Numerade Educator
06:15

Problem 132

A construction company is installing an iron culvert (a long cylindrical tube) that is $40.0 \mathrm{~m}$ long with a radius of $0.900 \mathrm{~m}$. To prevent corrosion, the culvert must be galvanized. This process is carried out by first passing an iron sheet of appropriate dimensions through an electrolytic cell containing $\mathrm{Zn}^{2+}$ ions, using graphite as the anode and the iron sheet as the cathode. If the voltage is $3.26 \mathrm{~V},$ what is the cost of electricity for depositing a layer $0.200 \mathrm{~mm}$ thick if the efficiency of the process is 95 percent? The electricity rate is $\$ 0.12$ per kilowatt hour $(\mathrm{kWh}),$ where $1 \mathrm{~W}=1 \mathrm{~J} / \mathrm{s}$ and the density of Zn is $7.14 \mathrm{~g} / \mathrm{cm}^{3}$.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
09:50

Problem 133

A $9.00 \times 10^{2}-\mathrm{mL} 0.200 \mathrm{M} \mathrm{MgI}_{2}$ was electrolyzed.
As a result, hydrogen gas was generated at the cathode and iodine was formed at the anode. The volume of hydrogen collected at $26^{\circ} \mathrm{C}$ and $779 \mathrm{mmHg}$ was $1.22 \times 10^{3} \mathrm{~mL}$. (a) Calculate the charge in coulombs consumed in the process. (b) How long (in min) did the electrolysis last if a current of $7.55 \mathrm{~A}$ was used? (c) A white precipitate was formed in the process. What was it and what was its mass in grams? Assume the volume of the solution was constant.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
04:21

Problem 134

Based on the following standard reduction potentials:
$$
\begin{aligned}
\mathrm{Fe}^{2+}(a q)+2 e^{-} & \longrightarrow \mathrm{Fe}(s) & & E_{1}^{\circ}=-0.44 \mathrm{~V} \\
\mathrm{Fe}^{3+}(a q)+e^{-} \longrightarrow \mathrm{Fe}^{2+}(a q) & & E_{2}^{\circ}=& 0.77 \mathrm{~V}
\end{aligned}
$$ calculate the standard reduction potential for the half-reaction
$$
\mathrm{Fe}^{3+}(a q)+3 e^{-} \longrightarrow \mathrm{Fe}(s) \quad E_{3}^{\circ}=?
$$

Rashmi Sinha
Rashmi Sinha
Numerade Educator
01:48

Problem 135

A galvanic cell is constructed by immersing a piece of copper wire in $25.0 \mathrm{~mL}$ of a $0.20 \mathrm{M} \mathrm{CuSO}_{4}$ solution and a zinc strip in $25.0 \mathrm{~mL}$ of a $0.20 \mathrm{M} \mathrm{ZnSO}_{4}$ solution. (a) Calculate the emf of the cell at $25^{\circ} \mathrm{C}$ and predict what would happen if a small amount of concentrated $\mathrm{NH}_{3}$ solution were added to (i) the $\mathrm{CuSO}_{4}$ solution and (ii) the $\mathrm{ZnSO}_{4}$ solution. Assume that the volume in each compartment remains constant at $25.0 \mathrm{~mL}$. (b) In a separate experiment, $25.0 \mathrm{~mL}$ of $3.00 \mathrm{M} \mathrm{NH}_{3}$ are added to the $\mathrm{CuSO}_{4}$ so-
lution. If the emf of the cell is $0.68 \mathrm{~V},$ calculate the formation constant $\left(K_{\mathrm{f}}\right)$ of $\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}^{2+}$

Manik Pulyani
Manik Pulyani
Numerade Educator
02:27

Problem 136

Calculate the equilibrium constant for the following reaction at $298 \mathrm{~K}:$
$$
\mathrm{Zn}(s)+\mathrm{Cu}^{2+}(a q) \longrightarrow \mathrm{Zn}^{2+}(a q)+\mathrm{Cu}(s)
$$

Shazia Naz
Shazia Naz
Numerade Educator
01:55

Problem 137

To remove the tarnish $\left(\mathrm{Ag}_{2} \mathrm{~S}\right)$ on a silver spoon, a student carried out the following steps. First, she placed the spoon in a large pan filled with water so the spoon was totally immersed. Next, she added a few tablespoonful of baking soda (sodium bicarbonate , which readily dissolved. Finally, she placed some aluminum foil at the bottom of the pan in contact with the spoon and then heated the solution to about $80^{\circ} \mathrm{C}$. After a few minutes, the spoon was removed and rinsed with cold water. The tarnish was gone and the spoon regained its original shiny appearance. (a) Describe with equations the electrochemical basis for the procedure. (b) Adding $\mathrm{NaCl}$ instead of $\mathrm{NaHCO}_{3}$ would also work because both compounds are strong electrolytes. What is the added advantage of using $\mathrm{NaHCO}_{3} ?$ (Hint:
Consider the $\mathrm{pH}$ of the solution. $)$ (c) What is the purpose of heating the solution? (d) Some commercial tarnish removers contain a fluid (or paste) that is a dilute $\mathrm{HCl}$ solution. Rubbing the spoon with the fluid will also remove the tarnish. Name two disadvantages of using this procedure compared to the one described above.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
02:43

Problem 138

The nitrite ion $\left(\mathrm{NO}_{2}^{-}\right)$ in soil is oxidized to nitrate ion $\left(\mathrm{NO}_{3}^{-}\right)$ by the bacteria Nitrobacter agilis in the presence of oxygen. The half-reduction reactions are
$$
\begin{aligned}
\mathrm{NO}_{3}^{-}+2 \mathrm{H}^{+}+2 e^{-} & \longrightarrow \mathrm{NO}_{2}^{-}+\mathrm{H}_{2} \mathrm{O} & & E^{\circ}=0.42 \mathrm{~V} \\
\mathrm{O}_{2}+4 \mathrm{H}^{+}+4 e^{-} & \longrightarrow & 2 \mathrm{H}_{2} \mathrm{O} & & E^{\circ}=1.23 \mathrm{~V}
\end{aligned}
$$
Calculate the yield of ATP synthesis per mole of nitrite oxidized. (Hint: See Section 17.7.)

Susan Hallstrom
Susan Hallstrom
Numerade Educator
03:29

Problem 138

The nitrite ion $\left(\mathrm{NO}_{2}^{-}\right)$ in soil is oxidized to nitrate ion $\left(\mathrm{NO}_{3}^{-}\right)$ by the bacteria Nitrobacter agilis in the presence of oxygen. The half-reduction reactions are
$\mathrm{NO}_{3}^{-}+2 \mathrm{H}^{+}+2 e^{-} \longrightarrow \mathrm{NO}_{2}^{-}+\mathrm{H}_{2} \mathrm{O} \quad E^{\circ}=0.42 \mathrm{~V}$
$$
\mathrm{O}_{2}+4 \mathrm{H}^{+}+4 e^{-} \longrightarrow 2 \mathrm{H}_{2} \mathrm{O} \quad E^{\circ}=1.23 \mathrm{~V}
$$
Calculate the yield of ATP synthesis per mole of nitrite oxidized. (Hint: See Section 17.7.)

Susan Hallstrom
Susan Hallstrom
Numerade Educator
14:44

Problem 139

The diagram here shows an electrolytic cell consisting of a Co electrode in a $2.0 \mathrm{M} \mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2}$ solution and a Mg electrode in a $2.0 \mathrm{M} \mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}$ solution.
(a) Label the anode and cathode and show the halfcell reactions. Also label the signs $(+$ or $-)$ on the battery terminals. (b) What is the minimum voltage to drive the reaction? (c) After the passage of $10.0 \mathrm{~A}$ for $2.00 \mathrm{~h}$ the battery is replaced with a voltmeter and the electrolytic cell now becomes a galvanic cell. Calculate $E_{\text {cell. }}$ Assume volumes to remain constant at $1.00 \mathrm{~L}$ in each compartment.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
02:37

Problem 140

Fluorine is a highly reactive gas that attacks water to form $\mathrm{HF}$ and other products. Follow the procedure in Problem 18.126 to show how you can determine indirectly the standard reduction for fluorine as shown in Table 18.1 .

Rashmi Sinha
Rashmi Sinha
Numerade Educator
06:49

Problem 141

Show a sketch of a galvanic concentration cell. Each compartment consists of a Co electrode in a $\mathrm{Co}\left(\mathrm{NO}_{3}\right)_{2}$ solution. The concentrations in the compartments are $2.0 \mathrm{M}$ and $0.10 \mathrm{M}$, respectively. Label the anode and cathode compartments. Show the direction of electron flow. (a) Calculate the $E_{\text {cell }}$ at $25^{\circ} \mathrm{C}$. (b) What are the concentrations in the compartments when the $E_{\text {cell }}$ drops to 0.020 V? Assume volumes to remain constant at $1.00 \mathrm{~L}$ in each compartment.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
07:04

Problem 142

The emf of galvanic cells varies with temperature (either increases or decreases). Starting with Equation ( 18.3 ), derive an equation that expresses $E_{\text {cell }}^{\circ}$ in terms of $\Delta H^{\circ}$ and $\Delta S^{\circ} .$ Predict whether $E_{\text {cell }}^{\circ}$ will increase or decrease if the temperature of a Daniell cell increases. Assume both $\Delta H^{\circ}$ and $\Delta S^{\circ}$ to be temperature independent.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
03:12

Problem 143

A concentration cell ceases to operate when the concentrations of the two cell compartments are equal. At this stage, is it possible to generate an emf from the cell by adjusting another parameter without changing the concentrations? Explain.

David Collins
David Collins
Numerade Educator
12:50

Problem 144

It has been suggested that a car can be powered from the hydrogen generated by reacting aluminum soda cans with a solution of lye (sodium hydroxide) according to the following reaction:

How many aluminum soda cans would be required to generate the same amount of chemical energy as contained in one tank of gasoline? Read the Chemistry in Action on aluminum recycling in Section $21.7,$ and comment on the cost and environmental impact of powering a car with aluminum cans.

Susan Hallstrom
Susan Hallstrom
Numerade Educator
02:14

Problem 145

Estimate how long it would take to electroplate a teaspoon with silver from a solution of $\mathrm{AgNO}_{3},$ assuming a constant current of 2 A.

David Collins
David Collins
Numerade Educator
02:47

Problem 146

The potential for a cell based on the standard hydrogen electrode and the half-reaction
$$
\mathrm{M}^{n+}(a q)+n e^{-} \longrightarrow \mathrm{M}(s)
$$
was measured at several concentrations of $\mathrm{M}^{n+}(a q)$ giving the following plot. What is the value of $n$ in the half-reaction?

David Collins
David Collins
Numerade Educator