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Chapter 19

Electrochemistry

Educators

ES

Problem 1

Define oxidation and reduction and explain the basic procedure for balancing redox reactions.

Linhan Y.
Numerade Educator

Problem 2

Explain the difference between a voltaic (or galvanic) electro-chemical cell and an electrolytic one.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 3

Which reaction (oxidation or reduction) occurs at the anode of a voltaic cell? What is the sign of the anode? Do electrons flow toward or away from the anode?

Linhan Y.
Numerade Educator

Problem 4

Which reaction (oxidation or reduction) occurs at the cathode of a voltaic cell? What is the sign of the cathode? Do electrons flow toward or away from the cathode?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 5

Explain the purpose of a salt bridge in an electrochemical cell.

Linhan Y.
Numerade Educator

Problem 6

Which unit is used to measure the magnitude of electrical current? Which unit is used to measure the magnitude of a potential difference? Explain how electrical current and potential difference differ.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 7

What is the definition of the standard cell potential (Ecell)? What does a large positive standard cell potential imply about the spontaneity of the redox reaction occurring in the cell? What does a negative standard cell potential imply about the reaction?

Aadit S.
Numerade Educator

Problem 8

Describe the basic features of a cell diagram (or line notation) for an electrochemical cell.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 9

Why do some electrochemical cells employ inert electrodes such as platinum?

Linhan Y.
Numerade Educator

Problem 10

Describe the standard hydrogen electrode (SHE) and explain its use in determining standard electrode potentials.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 11

How is the cell potential of an electrochemical cell (Ecell) related to the potentials of the half-cells?

Linhan Y.
Numerade Educator

Problem 12

Does a large positive electrode potential indicate a strong oxidizing agent or a strong reducing agent? What about a large negative electrode potential?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 13

Is a spontaneous redox reaction obtained by pairing any reduction half-reaction with one listed above it or with one listed below it in Table 19.1?

Linhan Y.
Numerade Educator

Problem 14

How can Table 19.1 be used to predict whether or not a metal will dissolve in HCl? In HNO3?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 15

Explain why Ecell, Grxn, and K are all interrelated.

Linhan Y.
Numerade Educator

Problem 16

Does a redox reaction with a small equilibrium constant (K < 1) have a positive or a negative Ecell? Does it have a positive or a negative Grxn?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 17

How does Ecell depend on the concentrations of the reactants and products in the redox reaction occurring in the cell? What effect does increasing the concentration of a reactant have on Ecell? Increasing the concentration of a product?

Aadit S.
Numerade Educator

Problem 18

Use the Nernst equation to show that Ecell = Ecell under standard conditions.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 19

What is a concentration electrochemical cell?

Linhan Y.
Numerade Educator

Problem 20

What are the anode and cathode reactions in a common dry-cell battery? In an alkaline battery?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 21

What are the anode and cathode reactions in a lead-acid storage battery? What happens when the battery is recharged?

Linhan Y.
Numerade Educator

Problem 22

What are the three common types of portable rechargeable batteries, and how does each one work?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 23

What is a fuel cell? What is the most common type of fuel cell, and what reactions occur at its anode and cathode?

Linhan Y.
Numerade Educator

Problem 24

The anode of an electrolytic cell must be connected to which terminal-positive or negative-of the power source?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 25

What species is oxidized, and what species is reduced in the electrolysis of a pure molten salt?

Linhan Y.
Numerade Educator

Problem 26

If an electrolytic cell contains a mixture of species that can be oxidized, how do you determine which species will actually be oxidized? If it contains a mixture of species that can be reduced, how do you determine which one will actually be reduced?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 27

Why does the electrolysis of an aqueous sodium chloride solution produce hydrogen gas at the cathode?

Linhan Y.
Numerade Educator

Problem 28

What is overvoltage in an electrochemical cell? Why is it important?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 29

How is the amount of current flowing through an electrolytic cell related to the amount of product produced in the redox reaction?

Linhan Y.
Numerade Educator

Problem 30

What is corrosion? Why is corrosion only a problem for some metals (such as iron)?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 31

Explain the role of each of the following in promoting corrosion: moisture, electrolytes, and acids.

Linhan Y.
Numerade Educator

Problem 32

How can the corrosion of iron be prevented?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 33

Balance each redox reaction occurring in acidic aqueous solution.
a. K(s) + Cr3+(aq)-Cr(s) + K+(aq)
b. Al(s) + Fe2+(aq)-Al3+(aq) + Fe(s)
c. BrO3-(aq) + N2H4(g)-Br-(aq) + N2(g)

Linhan Y.
Numerade Educator

Problem 34

Balance each redox reaction occurring in acidic aqueous solution.
a. Zn(s) + Sn2+(aq)-Zn2+(aq) + Sn(s)
b. Mg(s) + Cr3+(aq)-Mg2+(aq) + Cr(s)
c. MnO4-(aq) + Al(s)-Mn2+(aq) + Al3+(aq)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 35

Balance each redox reaction occurring in acidic aqueous solution.
a. PbO2(s) + I-(aq)-Pb2+(aq) + I2(s)
b. SO32-(aq) + MnO4-(aq)-SO42-(aq) + Mn2+(aq)
c. S2O32-(aq) + Cl2(g)-SO42-(aq) + Cl2(aq)

Linhan Y.
Numerade Educator

Problem 36

Balance each redox reaction occurring in acidic aqueous solution.
a. I-(aq) + NO2-(aq)-I2(s) + NO(g)
b. ClO4-(aq) + Cl-(aq)-ClO3-(aq) + Cl2(g)
c. NO3-(aq) + Sn2+(aq)-Sn4+(aq) + NO(g)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 37

Balance each redox reaction occurring in basic aqueous solution.
a. H2O2(aq) + ClO2(aq)-ClO2-(aq) + O2(g)
b. Al(s) + MnO4-(aq)-MnO2(s) + Al(OH)4-(aq)
c. Cl2(g)-Cl-(aq) + ClO-(aq)

Aadit S.
Numerade Educator

Problem 38

Balance each redox reaction occurring in basic aqueous solution.
a. MnO4-(aq) + Br-(aq)-MnO2(s) + BrO3-(aq)
b. Ag(s) + CN-(aq) + O2(g)-Ag(CN)2-(aq)
c. NO2-(aq) + Al(s)-NH3(g) + AlO2-(aq)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 39

Sketch a voltaic cell for each redox reaction. Label the anode and cathode and indicate the half-reaction that occurs at each electrode and the species present in each solution. Also indicate the direction of electron flow.
a. 2 Ag+(aq) + Pb(s)-2 Ag(s) + Pb2+(aq)
b. 2 ClO2(g) + 2 I-(aq)-2 ClO2-(aq) + I2(s)
c. O2(g) + 4 H+(aq) + 2 Zn(s)-2 H2O(l) + 2 Zn2+(aq)

Aadit S.
Numerade Educator

Problem 40

Sketch a voltaic cell for each redox reaction. Label the anode and cathode and indicate the half-reaction that occurs at each electrode and the species present in each solution. Also indicate the direction of electron flow.
a. Ni2+(aq) + Mg(s)-Ni(s) + Mg2+(aq)
b. 2 H+(aq) + Fe(s)-H2(g) + Fe2+(aq)
c. 2 NO3-(aq) + 8 H+(aq) + 3 Cu(s)-2 NO(g) + 4 H2O(l) + 3 Cu2+(aq)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 41

Calculate the standard cell potential for each of the electrochemical cells in Problem 39.

Aadit S.
Numerade Educator

Problem 42

Calculate the standard cell potential for each of the electrochemical cells in Problem 40.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 43

Consider the voltaic cell:

a. Determine the direction of electron flow and label the anode and the cathode.
b. Write a balanced equation for the overall reaction and calculate Ecell.
c. Label each electrode as negative or positive.
d. Indicate the direction of anion and cation flow in the salt bridge.

Linhan Y.
Numerade Educator

Problem 44

Consider the voltaic cell:

a. Determine the direction of electron flow and label the anode and the cathode.
b. Write a balanced equation for the overall reaction and calculate Ecell.
c. Label each electrode as negative or positive.
d. Indicate the direction of anion and cation flow in the salt bridge.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 45

Use line notation to represent each electrochemical cell in Problem 39.

Linhan Y.
Numerade Educator

Problem 46

Use line notation to represent each electrochemical cell in Problem 40.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 47

Make a sketch of the voltaic cell represented by the line notation. Write the overall balanced equation for the reaction and calculate Ecell.

Aadit S.
Numerade Educator

Problem 48

Make a sketch of the voltaic cell represented by the line notation. Write the overall balanced equation for the reaction and calculate Ecell.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 49

Determine whether or not each redox reaction occurs spontaneously in the forward direction.
a. Ni(s) + Zn2+(aq)-Ni2+(aq) + Zn(s)
b. Ni(s) + Pb2+(aq)-Ni2+(aq) + Pb(s)
c. Al(s) + 3 Ag+(aq)-Al3+(aq) + 3 Ag(s)
d. Pb(s) + Mn2+(aq)-Pb2+(aq) + Mn(s)

Linhan Y.
Numerade Educator

Problem 50

Determine whether each redox reaction occurs spontaneously in the forward direction.
a. Ca2+(aq) + Zn(s)-Ca(s) + Zn2+(aq)
b. 2 Ag+(aq) + Ni(s)-2 Ag(s) + Ni2+(aq)
c. Fe(s) + Mn2+(aq)-Fe2+(aq) + Mn(s)
d. 2 Al(s) + 3 Pb2+(aq)-2 Al3+(aq) + 3 Pb(s)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 51

Which metal could you use to reduce Mn2+ ions but not Mg2+ ions?

Linhan Y.
Numerade Educator

Problem 52

Which metal can be oxidized with an Sn2+ solution but not with an Fe2+ solution?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 53

Determine whether or not each metal dissolves in 1 M HCl. For those metals that dissolve, write a balanced redox reaction showing what happens when the metal dissolves.
a. Al
b. Ag
c. Pb

Aadit S.
Numerade Educator

Problem 54

Determine whether or not each metal dissolves in 1 M HCl. For those metals that dissolve, write a balanced redox reaction showing what happens when the metal dissolves.
a. Cu
b. Fe
c. Au

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 55

Determine whether or not each metal dissolves in 1 M HNO3. For those metals that dissolve, write a balanced redox reaction showing what happens when the metal dissolves.
a. Cu
b. Au

Linhan Y.
Numerade Educator

Problem 56

Determine whether or not each metal dissolves in 1 M HIO3. For those metals that dissolve, write a balanced redox equation for the reaction that occurs.
a. Au
b. Cr

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 57

Calculate Ecell for each balanced redox reaction and determine if the reaction is spontaneous as written.
a. 2 Cu(s) + Mn2+(aq)-2 Cu+(aq) + Mn(s)
b. MnO2(s) + 4 H+(aq) + Zn(s)-Mn2+(aq) + 2 H2O(l) + Zn2+(aq)
c. Cl2(g) + 2 F-(aq)-F2(g) + 2 Cl-(aq)

Aadit S.
Numerade Educator

Problem 58

Calculate Ecell for each balanced redox reaction and determine if the reaction is spontaneous as written.
a. O2(g) + 2 H2O(l) + 4 Ag(s)-4 OH-(aq) + 4 Ag+(aq)
b. Br2(l) + 2 I-(aq)-2 Br-(aq) + I2(s)
c. PbO2(s) + 4 H+(aq) + Sn(s)-Pb2+(aq) + 2 H2O(l) + Sn2+(aq)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 59

Which metal cation is the best oxidizing agent?
a. Pb2+
b. Cr3+
c. Fe2+
d. Sn2+

Linhan Y.
Numerade Educator

Problem 60

Which metal is the best reducing agent?
a. Mn
b. Al
c. Ni
d. Cr

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 61

Use tabulated electrode potentials to calculate Grxn for each reaction at 25 C.
a. Pb2+(aq) + Mg(s)-Pb(s) + Mg2+(aq)
b. Br2(l) + 2 Cl-(aq)-2 Br-(aq) + Cl2(g)
c. MnO2(s) + 4 H+(aq) + Cu(s)-Mn2+(aq) + 2 H2O(l) + Cu2+(aq)

Aadit S.
Numerade Educator

Problem 62

Use tabulated electrode potentials to calculate Grxn for each reaction at 25 C.
a. 2 Fe3+(aq) + 3 Sn(s)-2 Fe(s) + 3 Sn2+(aq)
b. O2(g) + 2 H2O(l) + 2 Cu(s)-4 OH-(aq) + 2 Cu2+(aq)
c. Br2(l) + 2 I-(aq)-2 Br-(aq) + I2(s)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 63

Calculate the equilibrium constant for each of the reactions in Problem 61.

Aadit S.
Numerade Educator

Problem 64

Calculate the equilibrium constant for each of the reactions in Problem 62.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 65

Calculate the equilibrium constant for the reaction between Ni2+(aq) and Cd(s) (at 25 C).

Aadit S.
Numerade Educator

Problem 66

Calculate the equilibrium constant for the reaction between Fe2+(aq) and Zn(s) (at 25 C).

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 67

Calculate Grxn and Ecell for a redox reaction with n = 2 that has an equilibrium constant of K = 25 (at 25 C).

Aadit S.
Numerade Educator

Problem 68

Calculate Grxn and Ecell for a redox reaction with n = 3 that has an equilibrium constant of K = 0.050 (at 25 C).

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 69

voltaic cell employs the following redox reaction:

Calculate the cell potential at 25 C under each set of conditions.
a. standard conditions
b. [Sn2+] = 0.0100 M; [Mn2+] = 2.00 M
c. [Sn2+] = 2.00 M; [Mn2+] = 0.0100 M

Aadit S.
Numerade Educator

Problem 70

A voltaic cell employs the redox reaction:

Calculate the cell potential at 25 C under each set of conditions.
a. standard conditions
b. [Fe3+] = 1.0 * 10-3 M; [Mg2+] = 2.50 M
c. [Fe3+] = 2.00 M; [Mg2+] = 1.5 * 10-3 M

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 71

An electrochemical cell is based on these two half-reactions:

Calculate the cell potential at 25 C.

Aadit S.
Numerade Educator

Problem 72

An electrochemical cell is based on these two half-reactions:

Calculate the cell potential at 25 C.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 73

A voltaic cell consists of a Zn>Zn2+ half-cell and a Ni>Ni2+ half-cell at 25 C. The initial concentrations of Ni2+ and Zn2+ are 1.50 M and 0.100 M, respectively.

a. What is the initial cell potential?
b. What is the cell potential when the concentration of Ni2+ has fallen to 0.500 M?
c. What are the concentrations of Ni2+ and Zn2+ when the cell potential falls to 0.45 V?

Aadit S.
Numerade Educator

Problem 74

A voltaic cell consists of a Pb>Pb2+ half-cell and a Cu>Cu2+ half-cell at 25 C. The initial concentrations of Pb2+ and Cu2+ are 0.0500 M and 1.50 M, respectively.

a. What is the initial cell potential?
b. What is the cell potential when the concentration of Cu2+ has fallen to 0.200 M?
c. What are the concentrations of Pb2+ and Cu2+ when the cell potential falls to 0.35 V?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 75

Make a sketch of a concentration cell employing two Zn>Zn2+ halfcells. The concentration of Zn2+ in one of the half-cells is 2.0 M, and the concentration in the other half-cell is 1.0 * 10-3 M. Label
the anode and the cathode and indicate the half-reaction occurring at each electrode. Also indicate the direction of electron flow.

Aadit S.
Numerade Educator

Problem 76

Consider the concentration cell:

a. Label the anode and cathode.
b. Indicate the direction of electron flow.
c. Indicate what happens to the concentration of Pb2+ in each half-cell.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 77

A concentration cell consists of two Sn>Sn2+ half-cells. The cell has a potential of 0.10 V at 25 C. What is the ratio of the Sn2+ concentrations in the two half-cells?

Aadit S.
Numerade Educator

Problem 78

A Cu/Cu2+ concentration cell has a voltage of 0.22 V at 25 C. The concentration of Cu2+ in one of the half-cells is 1.5 * 10-3 M. What is the concentration of Cu2+ in the other half-cell? (Assume the concentration in the unknown cell to be the lower of the two concentrations.)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 79

Determine the optimum mass ratio of Zn to MnO2 in an alkaline battery.

Aadit S.
Numerade Educator

Problem 80

What mass of lead sulfate is formed in a lead-acid storage battery when 1.00 g of Pb undergoes oxidation?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 81

Refer to the tabulated values of Gf in Appendix IIB to calculate Ecell for a fuel cell that employs the reaction between methane gas (CH4) and oxygen to form carbon dioxide and gaseous water.

Aadit S.
Numerade Educator

Problem 82

Refer to the tabulated values of Gf in Appendix IIB to calculate Ecell for a fuel cell that employs the following reaction: (Gf for HC2H3O2(g) = -374.2 kJ>mol.)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 83

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron.
a. Zn
b. Sn
c. Mn

Linhan Y.
Numerade Educator

Problem 84

Determine whether or not each metal, if coated onto iron, would prevent the corrosion of iron.
a. Mg
b. Cr
c. Cu

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 85

Consider the electrolytic cell:

a. Label the anode and the cathode and indicate the halfreactions occurring at each.
b. Indicate the direction of electron flow.
c. Label the terminals on the battery as positive or negative and calculate the minimum voltage necessary to drive the reaction.

Aadit S.
Numerade Educator

Problem 86

Draw an electrolytic cell in which Mn2+ is reduced to Mn and Sn is oxidized to Sn2+. Label the anode and cathode, indicate the direction of electron flow, and write an equation for the halfreaction occurring at each electrode. What minimum voltage is necessary to drive the reaction?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 87

Write equations for the half-reactions that occur in the electrolysis of molten potassium bromide.

Linhan Y.
Numerade Educator

Problem 88

Which products are obtained in the electrolysis of molten NaI?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 89

Write equations for the half-reactions that occur in the electrolysis of a mixture of molten potassium bromide and molten lithium bromide.

Aadit S.
Numerade Educator

Problem 90

Which products are obtained in the electrolysis of a molten mixture of KI and KBr?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 91

Write equations for the half-reactions that occur at the anode and cathode for the electrolysis of each aqueous solution:
a. NaBr(aq)
b. PbI2(aq)
c. Na2SO4(aq)

Aadit S.
Numerade Educator

Problem 92

Write equations for the half-reactions that occur at the anode and cathode for the electrolysis of each aqueous solution:
a. Ni(NO3)2(aq)
b. KCI(aq)
c. CuBr2(aq)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 93

Make a sketch of an electrolytic cell that electroplates copper onto other metal surfaces. Label the anode and the cathode and indicate the reactions that occur at each.

Aadit S.
Numerade Educator

Problem 94

Make a sketch of an electrolytic cell that electroplates nickel onto other metal surfaces. Label the anode and the cathode and indicate the reactions that occur at each.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 95

Copper can be electroplated at the cathode of an electrolytic cell by the half-reaction:

How much time does it take for 325 mg of copper to be plated at a current of 5.6 A?

Aadit S.
Numerade Educator

Problem 96

Silver can be electroplated at the cathode of an electrolytic cell by the half-reaction:

What mass of silver plates onto the cathode if a current of 6.8 A flows through the cell for 72 min?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 97

A major source of sodium metal is the electrolysis of molten sodium chloride. What magnitude of current produces 1.0 kg of sodium metal in 1 hour?

Aadit S.
Numerade Educator

Problem 98

What mass of aluminum metal can be produced per hour in the electrolysis of a molten aluminum salt by a current of 25 A?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 99

Consider the unbalanced redox reaction:

Balance the equation and determine the volume of a 0.500 M KMnO4 solution required to completely react with 2.85 g of Zn.

Linhan Y.
Numerade Educator

Problem 100

Consider the unbalanced redox reaction:

Balance the equation and determine the volume of a 0.850 M K2Cr2O7 solution required to completely react with 5.25 g of Cu.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 101

Consider the molecular view of an Al strip and Cu2+ solution. Draw a similar sketch showing what happens to the atoms and ions after the Al strip is submerged in the solution for a few minutes.

Aadit S.
Numerade Educator

Problem 102

Consider the molecular view of an electrochemical cell involving the overall reaction:

Draw a similar sketch of the cell after it has generated a substantial amount of electrical current.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 103

Determine whether HI can dissolve each metal sample. If it can, write a balanced chemical reaction showing how the metal dissolves in HI and determine the minimum volume of 3.5 M HI required to
completely dissolve the sample.
a. 2.15 g Al
b. 4.85 g Cu
c. 2.42 g Ag

Aadit S.
Numerade Educator

Problem 104

Determine if HNO3 can dissolve each metal sample. If it can, write a balanced chemical reaction showing how the metal dissolves in HNO3 and determine the minimum volume of 6.0 M HNO3 required to completely dissolve the sample.
a. 5.90 g Au
b. 2.55 g Cu
c. 4.83 g Sn

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 105

The cell potential of this electrochemical cell depends on the pH of the solution in the anode half-cell.

What is the pH of the solution if Ecell is 355 mV?

Aadit S.
Numerade Educator

Problem 106

The cell potential of this electrochemical cell depends on the gold concentration in the cathode half-cell.

What is the concentration of Au3+ in the solution if Ecell is 1.22V?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 107

Consider the reaction shown here occurring at 25 C.

Determine the value of Ecell and K for the reaction and complete the table.

Aadit S.
Numerade Educator

Problem 108

Consider the reaction shown here occurring at 25 C.

Determine Ecell K, and Grxn for the reaction and complete the table.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 109

A friend wants you to invest in a new battery she has designed that produces 24 V in a single voltaic cell. Why should you be wary of investing in such a battery?

Linhan Y.
Numerade Educator

Problem 110

What voltage can theoretically be achieved in a battery in which lithium metal is oxidized and fluorine gas is reduced? Why might such a battery be difficult to produce?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 111

A battery relies on the oxidation of magnesium and the reduction of Cu2+. The initial concentrations of Mg2+ and Cu2+ are 1.0 * 10-4 M and 1.5 M, respectively, in 1.0-liter half-cells.
a. What is the initial voltage of the battery?
b. What is the voltage of the battery after delivering 5.0 A for 8.0 h?
c. How long can the battery deliver 5.0 A before going dead?

Aadit S.
Numerade Educator

Problem 112

A rechargeable battery is constructed based on a concentration cell constructed of two Ag>Ag+ half-cells. The volume of each half-cell is 2.0 L, and the concentrations of Ag+ in the half-cells are 1.25 M and 1.0 * 10-3 M.
a. How long can this battery deliver 2.5 A of current before it dies?
b. What mass of silver is plated onto the cathode by running at 3.5 A for 5.5 h?
c. Upon recharging, how long would it take to redissolve 1.00 * 102 g of silver at a charging current of 10.0 amps?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 113

If a water electrolysis cell operates at a current of 7.8 A, how long will it take to generate 25.0 L of hydrogen gas at a pressure of 25.0 atm and a temperature of 25 C?

Aadit S.
Numerade Educator

Problem 114

One type of breathalyzer employs a fuel cell to measure the quantity of alcohol in the breath. When a suspect blows into the breathalyzer, ethyl alcohol is oxidized to acetic acid at the anode:

At the cathode, oxygen is reduced:

The overall reaction is the oxidation of ethyl alcohol to acetic acid and water. When a suspected drunk driver blows 188 mL of his breath through this breathalyzer, the breathalyzer produces an average of 324 mA of current for 10 s. Assuming a pressure of 1.0 atm and a temperature of 25 C what percent (by volume) of the driver's breath is ethanol?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 115

The Ksp of CuI is 1.1 * 10-12. Find Ecell for the cell:

Aadit S.
Numerade Educator

Problem 116

The Ksp of Zn(OH)2 is 1.8 * 10-14. Find Ecell for the half-reaction:

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 117

Calculate Grxn and K for each reaction.
a. The disproportionation of Mn2+(aq) to Mn(s) and MnO2(s) in acid solution at 25 C.
b. The disproportionation of MnO2(s) to Mn2+(aq) and MnO4-(aq) in acid solution at 25 C.

Aadit S.
Numerade Educator

Problem 118

Calculate Grxn and K for each reaction.
a. The reaction of Cr2+(aq) with Cr2O72-(aq) in acid solution to form Cr3+(aq).
b. The reaction of Cr3+(aq) and Cr(s) to form Cr2+(aq). [The electrode potential of Cr2+(aq) to Cr(s) is -0.91 V.]

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 119

The molar mass of a metal (M) is 50.9 g/mol; it forms a chloride of unknown composition. Electrolysis of a sample of the molten chloride with a current of 6.42 A for 23.6 minutes produces 1.20g of M at the cathode. Determine the empirical formula of the chloride.

Aadit S.
Numerade Educator

Problem 120

A metal forms the fluoride MF3. Electrolysis of the molten fluoride by a current of 3.86 A for 16.2 minutes deposits 1.25 g of the metal. Calculate the molar mass of the metal.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 121

A sample of impure tin of mass 0.535 g is dissolved in strong acid to give a solution of Sn2+. The solution is then titrated with a 0.0448 M solution of NO3 -, which is reduced to NO(g). The
equivalence point is reached upon the addition of 0.0344 L of the NO3- solution. Find the percent by mass of tin in the original sample, assuming that it contains no other reducing agents.

Aadit S.
Numerade Educator

Problem 122

A 0.0251-L sample of a solution of Cu+ requires 0.0322 L of 0.129M KMnO4 solution to reach the equivalence point. The products of the reaction are Cu2+ and Mn2+. What is the concentration of the Cu2+ solution?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 123

A current of 11.3 A is applied to 1.25 L of a solution of 0.552 M HBr, converting some of the H+ to H2(g), which bubbles out of the solution. What is the pH of the solution after 73 minutes?

Aadit S.
Numerade Educator

Problem 124

A 215 mL sample of a 0.500 M NaCl solution with an initial pH of 7.00 is subjected to electrolysis. After 15.0 minutes, a 10.0 mL portion (or aliquot) of the solution is removed from the cell and titrated with 0.100 M HCl solution. The endpoint in the titration is reached upon addition of 22.8 mL of HCl. Assuming constant current, how much current (in A) was running through the cell?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 125

An MnO2(s)>Mn2+(aq) electrode in which the pH is 10.24 is prepared. Find the [Mn2+] necessary to lower the potential of the half-cell to 0.00V (at 25 C).

Aadit S.
Numerade Educator

Problem 126

To what pH should you adjust a standard hydrogen electrode to achieve an electrode potential of -0.122 V? (Assume that the partial pressure of hydrogen gas remains at 1 atm.)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 127

Suppose a hydrogen-oxygen fuel-cell generator produces electricity for a house. Use the balanced redox reactions and the standard cell potential to predict the volume of hydrogen gas (at STP) required each month to generate the electricity. Assume the home uses 1.2 * 103 kWh of electricity per month.

Aadit S.
Numerade Educator

Problem 128

A voltaic cell designed to measure [Cu2+] is constructed of a standard hydrogen electrode and a copper metal electrode in the Cu2+ solution of interest. If you want to construct a calibration curve for how the cell potential varies with the concentration of copper(II), what do you plot in order to obtain a straight line? What is the slope of the line?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 129

The surface area of an object to be gold plated is 49.8 cm2, and the density of gold is 19.3 g>cm3. A current of 3.25 A is applied to a solution that contains gold in the +3 oxidation state. Calculate the time required to deposit an even layer of gold 1.00 * 10-3 cm thick on the object.

Aadit S.
Numerade Educator

Problem 130

Electrodepositing all the Cu and Cd from a solution of CuSO4 and CdSO4 required 1.20 F of electricity (1 F = 1 mol e-). The mixture of Cu and Cd that was deposited had a mass of 50.36 g. What mass of CuSO4 was present in the original mixture?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 131

Sodium oxalate, Na2C2O4, in solution is oxidized to CO2(g) by MnO4-, which is reduced to Mn2+. A 50.1-mL volume of a solution of MnO4- is required to titrate a 0.339 g sample of sodium oxalate. This solution of MnO4- is used to analyze uranium-containing samples. A 4.62-g sample of a uranium-containing material requires 32.5 mL of the solution for titration. The oxidation of the uranium can be represented by the change UO2+-UO22+. Calculate the percentage of uranium in the sample.

Aadit S.
Numerade Educator

Problem 132

Three electrolytic cells are connected in a series. The electrolytes in the cells are aqueous copper(II) sulfate, gold(III) sulfate, and silver nitrate. A current of 2.33 A is applied, and after some time 1.74 g Cu is deposited. How long was the current applied? What mass of gold and silver was deposited?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 133

The cell Pt(s) Cu+(1 M), Cu2+(1 M) }Cu+(1 M) Cu(s) has Ecell = 0.364 V. The cell Cu(s) Cu2+(1 M) }Cu+1(1 M) Cu(s) has Ecell = 0.182 V. Write the cell reaction for each cell and explain the differences in Ecell. Calculate G for each cell reaction to help explain these differences.

Aadit S.
Numerade Educator

Problem 134

An electrochemical cell has a positive standard cell potential but a negative cell potential. Which statement is true?
a. K 7 1; Q 7 K
b. K 6 1; Q 7 K
c. K 7 1; Q 6 K
d. K 6 1; Q 6 K

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 135

Which oxidizing agent oxidizes Br- but not Cl-?
a. K2Cr2O7 (in acid)
b. KMnO4 (in acid)
c. HNO3

Aadit S.
Numerade Educator

Problem 136

A redox reaction employed in an electrochemical cell has a negative Grxn. Which statement is true?
a. Ecell is positive; K < 1
b. Ecell is negative; K > 1
c. Ecell is negative; K > 1
d. Ecell is positive; K < 1

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 137

A redox reaction has an equilibrium constant of K = 0.055. What is true of Grxn and Ecell for this reaction?

Aadit S.
Numerade Educator

Problem 138

Balance the redox reactions by following the steps in the text. Rotate through the group, having each group member do the next step in the process and explaining that step to the rest of the group.
a. I2(s) + Fe(s)-FeI2(s)
b. Cl2(g) + H2O2(aq)-Cl-(aq) + O2(g) (acidic)
c. Hg2+(aq) + H2(g)-Hg(l) + H2O(l) (basic)
d. CH3OH(l) + O2(g)-CO2(g) + H2O(l) (acidic)

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 139

Have each group member select a half-reaction from Table 19.1. Each member should calculate the standard cell potential of an electrochemical cell formed between each member's half-reaction and the half-reaction of each of the other group members. For each pair of half-reactions, write the overall balanced chemical reaction that is spontaneous.

Check back soon!

Problem 140

Calculate Go and K for each reaction the group created in Question 139. For one of the reactions, explain how the sign or magnitude of each quantity (Ecell, G, and K) is consistent with the fact that the reaction is spontaneous in the direction written.

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 141

Design a device that uses an electrochemical cell to determine the amount of Cu2+ in a sample of water. Describe, in detail, the construction and the theory of operation of your device. If you are able to measure voltage with one-millivolt accuracy, what will be the uncertainty in your measured concentration?

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Problem 142

Using a library or the Internet, research a fuel cell that uses methanol for fuel. What is the reaction at the anode? What is the reaction at the cathode? What is the overall reaction? What is the standard cell potential? How many kWh can it generate from 1 L (0.792 kg) of methanol?

ES
Eugene S.
University of Minnesota - Twin Cities

Problem 143

In this chapter, you have seen that the voltage of an electrochemical cell is sensitive to the concentrations of the reactants and products in the cell. As a result, electrochemical cells can be used to measure the concentrations of certain species in solution. For example, the voltage of an electrochemical cell based on the reaction H2(g) + Cu2+(aq)-2 H+ + Cu(s) is sensitive to both the Cu2+ concentration and the H+ concentration in solution. If the H+ concentration is held constant, then the voltage only depends on the Cu2+ concentration, and we can use the cell to measure the Cu2+ concentration in an unknown solution. The tabulated data show the measured voltage in the hydrogen/copper electrochemical cell just discussed for several Cu2+ concentrations. Examine the data and answer the questions that follow.

a. Construct a graph of the measured voltage versus the the copper concentration. Is the graph linear?
b. Determine how you might manipulate the data to produce a linear graph. (Hint: See the Nernst equation.)
c. Reconstruct a graph of the data using the method to produce a linear graph from part b. Determine the slope and y-intercept of the best-fitting line to the points in your graph. Could you have predicted the slope and intercept from the Nernst equation?
d. The voltage of two unknown solutions are measured and recorded. Use the slope and intercept from part c to determine the Cu2+ concentrations of the unknown solutions.

Aadit S.
Numerade Educator