Deck 18: Electrochemistry and Its Applications

Question 1

The unit used to measure electrical current is the

A) ampere
B) coulomb
C) faraday
D) joule
E) volt

Answer 1

ampere

Question 2

The unit used to measure electromotive force (emf) is the

A) horsepower
B) electromagnetic Faraday
C) volt
D) coulomb
E) ampere

Answer 2

horsepower

Question 3

Consider an electrochemical cell as shown, with Zn in ZnCl₂(aq) and Cu in Cu(NO₃)₂(aq), and a salt bridge containing KNO₃(aq). The overall chemical reaction is

Which statement is correct?

A) one mole of electrons is transferred in this reaction
B) copper is oxidized at the anode
C) electrons travel from the Zn electrode to the Cu electrode
D) this is an example of a concentration cell
E) zinc is reduced at the cathode

Answer 3

electrons travel from the Zn electrode to the Cu electrode

Question 4

Which cell notation represents a battery constructed using zinc and iron electrodes with electrons flowing from zinc to iron?

A) Fe³⁺(aq) | Fe²⁺(aq) || Zn(s) | Zn²⁺(aq)
B) Fe³⁺(aq) | Fe(s) || Zn(s) | Zn²⁺(aq)
C) Zn(s) | Zn²⁺(aq) || Fe³⁺(aq) | Fe²⁺(aq)
D) Zn(s) | Zn²⁺(aq) || Fe³⁺(aq) | Fe(s)
E) Zn(s) | Zn²⁺(aq) || Fe(s) | Fe³⁺(aq)

Question 5

In the salt bridge in an electrochemical cell,

A) negatively charged ions migrate towards the anode compartment
B) positively charged ions migrate towards the anode compartment
C) negatively charged ions migrate towards the cathode compartment
D) both b and c
E) neither a nor c

Question 6

In the anode compartment of a simple electrochemical cell the electrode is being ____, and ____ are flowing in from the salt bridge.

A) oxidized; anions
B) oxidized; cations
C) oxidized; electrons
D) reduced; cations
E) reduced; anions

Question 7

Which statement is not correct?

A) an electrochemical cell can extract electrical energy from a reactant-favored chemical reaction
B) all electrochemical cells have at least two electrodes
C) a voltaic cell is a type of electrochemical cell
D) reduction occurs at the cathode in an electrochemical cell
E) a battery is an example of an electrochemical cell

Question 8

Select the material containing the element with the highest oxidation number and determine how many electrons are required to reduce that element to an oxidation number of zero.

A) 8
B) 7
C) 6
D) 4
E) 3

Question 9

Which change does not indicate a reduction?

A) decrease in oxidation number
B) gain of electrons
C) electrons as reactants
D) reactant acting as a reducing agent
E) pure oxygen becoming oxide ion

Question 10

If cadmium metal and the Fe(III) ion are mixed in aqueous solution, a solution containing Cd(II) and Fe(II) results. The balanced equation for this process is

A) Cd(s) + Fe³⁺(aq) Fe²⁺(aq) + Cd²⁺(aq)
B) Cd(s) + 2 Fe³⁺(aq) 2 Fe²⁺(aq) + Cd²⁺(aq)
C) 2 Cd(s) + Fe³⁺(aq) Fe²⁺(aq) + 2 Cd²⁺(aq)
D) 2 Cd(s) + Fe³⁺(aq) 2 Fe²⁺(aq) + Cd²⁺(aq)

Question 11

Which statement is correct?

A) all electrolytic cells are voltaic cells
B) all voltaic cells are electrolytic cells
C) metals corrode by an electrolytic process
D) voltaic cells and electrolytic cells are both electrochemical cells
E) all electrochemical cells are electrolytic cells

Question 12

Which compound contains the atom with the highest oxidation number?

A) FeCl₃
B) SnH₄
C) NaClO₄
D) CrO₃
E) H₂O₂

Question 13

Which is not true of the standard conditions for electrochemical cell measurements?

A) the cell voltage is always positive
B) solutes are at 1.0 M concentration
C) solids are in the pure state
D) liquids are in the pure state
E) gases are at 1 bar pressure

Question 14

Which change describes an oxidation half-reaction?

A) decrease in oxidation number
B) loss of electrons
C) electrons as reactants
D) reactant acting as an oxidizing agent
E) pure oxygen becoming oxide ion

Question 15

In the reaction shown below, ____ is the oxidizing agent and ____ the reducing agent.

A) Zn²⁺; H₂
B) Zn; H⁺
C) H₂; Zn²⁺
D) H⁺; Zn²⁺
E) H⁺; Zn

Question 16

The study of the relationships between electron flow and redox reactions is called

A) nuclear chemistry.
B) electrochemistry.
C) thermodynamics.
D) electrodynamics.
E) inorganic chemistry.

Question 17

Which of these components must be present in a redox reaction?

A) a substance present as an element which becomes incorporated into a molecule, or vice versa
B) an atom whose oxidation number increases
C) an atom whose oxidation number decreases
D) either b or c
E) both b and c

Question 18

A voltaic cell is one in which

A) the standard reduction potentials of the two half-cell reactions are equal to one another
B) the standard cell voltage is positive
C) the standard cell voltage is negative
D) both a and b are correct
E) both a and c are correct

Question 19

Exhibit 18-2 Use this list of half-reactions to answer the following question(s).

Refer to Exhibit 18-2. How many different cells with E ^$\circ$ _cell in excess of +1.90 V can be constructed using the half-reactions given in the table?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 20

When the reaction shown below is balanced, the coefficients are ____, and ____ electrons are transferred.

A) 1, 3, 1, and 3; 6
B) 2, 3, 2, and 3; 6
C) 3, 2, 3, and 2; 6
D) 2, 3, 2, and 3; 12
E) 3, 2, 3, and 2; 12

Question 21

The value of E ^$\circ$ _cell for the cell shown below is + 1.41 V.
What is the value of E_cell at 25 ^$\circ$ C if the concentration of Al³⁺(aq) is 0.050 M, and of Ni²⁺(aq), 2.0 M?

A) +1.34 V
B) +1.38 V
C) +1.41 V
D) +1.44 V
E) +1.48 V

Question 22

The value of E ^$\circ$ _cell for an aluminum-nickel electrochemical cell is +1.41 V at 25 ^$\circ$ C. The value of K ^$\circ$ for this cell under standard conditions is

A) <<0.01
B) » 0.01
C) » 1
D) » 100
E) >>100

Question 23

Exhibit 18-2 Use this list of half-reactions to answer the following question(s).
Refer to Exhibit 18-2. The strongest reducing agent in the table is

A) Al(s).
B) Al³⁺(aq).
C) H⁺(aq).
D) MnO₄^-(aq).
E) Mn²⁺(aq).

Question 24

The value of E ^$\circ$ _cell for an aluminum-nickel electrochemical cell is +1.41 V at 25 ^$\circ$ C. Calculate the value of DG ^$\circ$ for this cell under standard conditions.

A) -816 kJ
B) -680 kJ
C) -272 kJ
D) +403 kJ
E) +680 kJ

Question 25

An electrolytic reaction is a system in which

A) the reaction conditions are manipulated to change the value of E ^$\circ$ _cell to a favorable one.
B) a reactant-favored reaction is forced to produce electricity by the input of heat or light.
C) the same element is both oxidized and reduced.
D) electricity is used to produce a chemical reaction.
E) a chemical reaction is used to produce electricity.

Question 26

Calculate the value of E_cell for a zinc-platinum electrochemical cell when the concentration of Pt²⁺(aq) is 0.050 M and the concentration of Zn²⁺(aq) is 1.1 M. E ^$\circ$ _cell = 1.96 V under standard conditions. Pt is the less active metal.

A) 2.04 V
B) 2.00 V
C) 1.96 V
D) 1.92 V
E) 1.88 V

Question 27

Exhibit 18-2 Use this list of half-reactions to answer the following question(s).
Refer to Exhibit 18-2. The strongest oxidizing agent in the table is

A) Al(s)
B) Al³⁺(aq)
C) H⁺(aq)
D) MnO₄^-(aq)
E) Mn²⁺(aq)

Question 28

A mass of 0.839 g of a divalent metal is plated out of a solution of the divalent metal ion. This takes 67.2 min at a current of 0.63 A. What is the metal? (Hint: find its atomic mass.)

A) Cd
B) Cu
C) Hg
D) Fe
E) Mg

Question 29

Consider the cell reaction The value of E ^$\circ$ _cell is 0.447 V at 25 ^$\circ$ C. Calculate the value of DG ^$\circ$ and K for this cell.

A) -86.3 kJ; 1.26 × 10¹⁵
B) -43.1 kJ; 1.37 × 10⁴³
C) 43.1 kJ; 3.55 × 10⁷
D) 86.3 kJ; 7.92 × 10^-16
E) 86.3 kJ; 2.00 × 10⁸⁶

Question 30

Which process could not be an electrolytic reaction?

A) 2 H₂O(l) 2 H₂(g) + O₂(g)
B) 2 Al₂O₃(l) 4 Al(l) + 3 O₂(g)
C) Na⁺(aq) + Cl^-(aq) 2 Na(l) + Cl₂(g)
D) 2 Fe(s) + 3 O₂(g) Fe₂O₃(s)
E) 2 PbSO₄(s) + 4 H₂O(l) Pb(s) + PbO₂(s) + 2 H₂SO₄(aq)

Question 31

Which statement about lead storage batteries is not correct?

A) The value of E ^$\circ$ _cell is slightly more than 2 V
B) The anode reaction involves the conversion of Pb to Pb²⁺
C) Nitric acid serves as the electrolyte
D) The cathode reaction involves the conversion of Pb⁴⁺ to Pb²⁺
E) In order to provide 12 volts, the battery consists of six cells

Question 32

Exhibit 18-2 Use this list of half-reactions to answer the following question(s).
Refer to Exhibit 18-2. The potential for the product-favored reaction involving aluminum and copper metals, Al³⁺(aq) and Cu²⁺(aq), is

A) 2.17 V.
B) 2.00 V.
C) 1.79 V.
D) 1.32 V.
E) 1.15 V.

Question 33

Which statement concerning the proton exchange membrane fuel cell is not correct?

A) At the anode, hydrogen gas is reduced to form water.
B) At the cathode, oxygen is reduced to water.
C) The cell uses platinum as a catalyst.
D) The actual fuel cell reaction causes no pollution of any kind.
E) A limiting factor is the cost of producing hydrogen as the fuel.

Question 34

Which of the following would require the most Faradays of electricity?

A) converting 2.0 mol of Al³⁺ into Al
B) converting 2.0 mol of Cr³⁺ into Cr
C) converting 1.5 mol of Cr⁶⁺ into Cr
D) converting 3.0 mol of Sn⁴⁺ into Sn²⁺
E) converting 2.0 mol of Sn⁴⁺ into Sn

Question 35

A fuel cell is

A) an electrolytic cell that is used to supply electrical power
B) an electrochemical cell that converts chemical energy directly into electricity
C) a cell in which a hydrogen-oxygen is ignited to produced electricity
D) typically not susceptible to contamination
E) currently both technically feasible and commercially viable as a source of electrical power

Question 36

The relationship between Gibbs free energy and E ^$\circ$ _cell is DG ^$\circ$ =

A)
B)
C) -nFE ^$\circ$ _cell.
D) nFE ^$\circ$ _cell.
E) -RT ln K.

Question 37

Exhibit 18-2 Use this list of half-reactions to answer the following question(s).
Refer to Exhibit 18-2. Which of these combinations would result in a spontaneous reaction?

A) Al³⁺(aq) and Cr³⁺(aq)
B) Al³⁺(aq) and Cu(s)
C) Cr₂O₇^2-(aq) and MnO₄^-(aq)
D) Cu(s) and MnO₄^-(aq)
E) Pt(s) and Pb²⁺(aq)

Question 38

The value of E_cell at 25 ^$\circ$ C for the cell shown below is +1.27 V. What is the value of E ^$\circ$ _cell?

A) 1.57 V
B) 1.28 V
C) 1.26 V
D) 1.23 V
E) 0.97 V

Question 39

A secondary cell is one which ____; this is possible because ____.

A) is driven by a primary cell; the cell reactions are coupled
B) is disposable without harming the environment; no mercury is used
C) is rechargeable; the cell reaction is reversible
D) has double the lifetime of a primary cell; two primary cells are placed in parallel
E) has double the voltage of a primary cell; two primary cells are placed in series

Question 40

A primary battery is one in which

A) the electrochemical reactions can be easily reversed
B) the electrochemical reactions cannot be easily reversed
C) the battery is "dead" and it must be discarded
D) the cell is rechargeable
E) both b and c are correct

Question 41

Is the part of a flashlight battery that is marked "+" the anode or the cathode? Explain why it is labeled in that way.

Question 42

Explain why galvanizing steel chain-link fencing is a more effective strategy to prevent corrosion than simply painting it.

Question 43

Galvanizing a metal (coating its surface with zinc) to prevent corrosion works because

A) the coating limits access of oxygen to the metal surface
B) the coating reacts to give an impermeable layer of zinc hydroxide
C) the zinc coating provides cathodic protection
D) of reasons a and b.
E) of reasons a, b, and c.

Question 44

Calculate the time needed to plate out 175 g of nickel from a Ni²⁺ solution when a current of 10.0 A is applied.

A) 4.00 hr
B) 8.00 hr
C) 9.40 hr
D) 16.0 hr
E) 32.0 hr

Question 45

Refer to the following values of standard reduction potentials.
a. Write the balanced overall reaction for gold reacting with zinc(II) ion.
b. Calculate the value of E°_cell for the reaction.
c. How many electrons are transferred in this reaction? Explain.
d. Calculate the value of DG° for this cell at 25°C.
e. Is this reaction product-favored or reactant-favored? Explain how your answers in Parts b, d, and e support this conclusion.

Question 46

Calculate the mass of cobalt that will be deposited when a current of 2.00 A is passed through a solution of CoSO₄ for 10.0 hours.

A) 6.11 × 10^-3 g
B) 0.366 g
C) 4.40 g
D) 8.72 g
E) 22.0 g

Question 47

Unwanted oxidation of a metal exposed to the environment is

A) galvanization.
B) electroplating.
C) electrolysis.
D) corrosion.
E) cathodic protection.

Question 48

Which statement concerning the number of electrons involved in electrolysis is not correct?

A) The total charge is obtained by multiplying the current in amps by the time in seconds.
B) The charge associated with one mole of electrons is called the Faraday.
C) In producing one mole of Cl₂(g) from Cl^-(aq), one mole of electrons is produced.
D) When one mole of Fe(s) is produced from Fe³⁺(aq), three moles of electrons are needed.
E) Electroplating of one mole of silver from a solution of silver ions requires one mole of electrons.

Question 49

Although aluminum is a moderately reactive metal, it can be regarded as unreactive in everyday use because a layer of aluminum oxide coats the surface and prevents further oxidation. This is an example of

A) anodic inhibition.
B) cathodic inhibition.
C) galvanization.
D) cathodic protection.
E) anodic protection.

Question 50

Explain, with reference to the Nernst equation, how it is possible for a cell to have a positive cell potential under standard conditions, but a negative cell potential under other conditions.

Question 51

Answer the following questions:
a. Briefly explain why aluminum is usually isolated from its ore by electrolysis, not by chemical reduction.
b. Explain why this electrolysis has to be performed on a molten aluminum salt, not in aqueous solution.

Question 52

If all of the following metals are part of a metal piping system, and an electrolyte solution is pumped through the system, which metal will corrode the most?

A) Cu (E ^$\circ$ _anode = +0.34 V)
B) Fe (E ^$\circ$ _anode = -0.44 V)
C) Sn (E ^$\circ$ _anode = -0.14 V)
D) Mg (E ^$\circ$ _anode = -2.37 V)
E) Ni (E ^$\circ$ _anode = -0.25 V)

Question 53

An underground steel fuel pipe buried in an area that is infiltrated by sea water could be protected against corrosion by using

A) anodic inhibition
B) cathodic protection
C) both anodic inhibition and cathodic protection
D) any of these methods would be effective
E) none of these methods would be effective

Question 54

Balance the following redox equation.
The oxidation process is clearly