Reduction-Oxidation Reactions and Electrochemistry MCQ
- In recitation, you studied the electrochemistry
involved in the "fruit clock". If an orange is used to power the
fruit clock, which of the following statements is TRUE?
- Free electrons flow through the orange to maintain
electrical neutrality.
- The orange allows the Zn2+ and Cu2+
ions produced in the reaction to mix thereby maintaining electrical
neutrality.
- The orange functions as the anode.
- The orange functions as the salt bridge by maintaining
electrical neutrality.
- The acids present in the orange are oxidized at the
anode to produce hydrogen gas.
- Which of the following reactions IS a
reduction-oxidation reaction?
- formation of N2 in automobile airbags: 2NaN3(s)
--> 2Na(l) + 3N2(g)
- combustion of propane in a gas grill: C3H8(g)
+ 5O2(g) --> 3CO2(g) + 4H2O(g)
- decomposition of hydrogen peroxide (H2O2)
by light: 2H2O2(aq) --> 2H2O(l) + O2(g)
- All of these are reduction-oxidation reactions.
- None of these are reduction-oxidation reactions.
- Which of the following metals could be used
successfully to galvanize iron?
- Ni
- Cu
- Sn
- Co
- Mn
- Calculate the standard cell potential (in V) for the
following reaction at 25oC.
2Cr(s)
+ 3Ni2+(aq) --> 2Cr3+(aq) + 3Ni(s)
- The layer of zinc on a piece of galvanized iron can be
removed by placing it in a concentrated solution of acid. Calculate the
standard cell potential (in V) for this reaction.
- A beaker contains a small amount of gold dust (Au(s)).
Which of the following aqueous solutions, when added to the beaker, would
dissolve the gold dust (i.e., convert Au(s) to Au3+(aq))?
- Cr2O72- (acidic
solution)
- H2O2 (acidic solution)
- Br2
- Zn2+
- Al3+
- Which of the following statements best describes what
will happen when liquid bromine (Br2) is poured into a beaker
containing aluminum metal?
- Br2 will be reduced; Al will be oxidized
- Br2 will be oxidized; Al will be reduced
- Br2 will function as the reducing agent; Al
will function as the oxidizing agent
- A reaction will not occur.
- It is impossible to tell.
- Consider the following galvanic cell reaction at 25oC,
4Cr2+(aq)
+ O2(g) + 4H3O+(aq) --> 4Cr3+(aq)
+ 6H2O(l)
Which of the following statements
best describes what would happen to the cell potential if the concentration of
Cr2+ is increased?
- The cell potential would become less positive.
- The cell potential would become more positive.
- The cell potential would remain the same.
- It is impossible to tell.
- Which of the following half-reactions is involved in
the STANDARD HYDROGEN ELECTRODE?
- Pt2+(aq) + 2e- --> Pt(s)
- 2H3O+(aq) + 2e-
--> 2H2O(l) + H2(g)
- H2O2(aq) + 2H3O+(aq)
+ 2e- --> 4H2O(l)
- O2(g) + 2H2O(l) + 4e-
--> 4OH-(aq)
- None of the above.
- A concentration cell containing aqueous solutions of
Cu(NO3)2 and solid copper metal is constructed so
that the Cu2+ ion concentration in the cathode half-cell is
0.66 M. Calculate the concentration of the Cu2+ ion in the
anode half-cell if the cell potential for the concentration cell at 25oC
is 0.034 V.
- Consider a galvanic cell based on the following overall
reaction,
Fe(s)
+ 2Ag+(aq) --> Fe2+(aq) + 2Ag(s)
Calculate the cell potential (in V)
for this reaction at 25oC when the concentration of Ag+
ions is 0.050 M and the concentration of Fe2+ ions is 1.50 M.
- Which of the following metal ions will plate out on a
piece of galvanized iron which has NOT had the layer of Zn metal
removed?
- Cu2+
- Au3+
- Ni2+
- All of these.
- None of these.
- Which of the following best explains why concentration
cells must be run under non-standard conditions in order for them to do
electrical work?
- A concentration cell can only do electrical work when
either NH3 or NaOH is added to one of the half-cells.
- A concentration cell cannot do electrical work at 25oC.
- The change in free energy for a concentration cell is
always negative under standard conditions.
- A concentration cell has a cell potential equal to
zero under standard conditions.
- A concentration cell can only do electrical work when
the cell is run under standard conditions.
- Which of the following statements about a salt bridge
in a voltaic cell is TRUE?
- Free electrons flow through the salt bridge to
maintain electrical neutrality in the two half-cells.
- The salt bridge allows the ions present in the two
half-cells to mix extensively.
- The wire must be connected directly to the salt bridge
in order for the salt bridge to be able to maintain electrical neutrality
in the two half-cells.
- In some cases, a salt bridge functions as the anode.
- Ions from the electrolyte in the salt bridge flow into
each half-cell to maintain electrical neutrality.
- Which of the following reactions can be used to
construct a voltaic cell?
- H3O+(aq) + OH-(aq)
<==> 2H2O(l)
- HF(g) + H2O(l) <==> H3O+(aq)
+ F-(aq)
- Cu2+(aq) + 4F-(aq) <==>
CuF42-(aq)
- O2(g) + 4H3O+(aq) +
4I-(aq) <==> 2I2(aq) + 6H2O(l)
- 2NO2(g, nitrogen dioxide) <==> N2O4(g,
dinitrogen tetroxide)
- Consider the following standard reduction potentials,
half
reaction
|
Eo, V
|
Fe3+(aq)
+ e- <==> Fe2+(aq)
|
0.77
|
H2O2(aq) + 2e- <==>
2OH-(aq)
|
0.88
|
- For the voltaic cell reaction below, calculate the Fe2+
concentration (in M) that would be needed to produce a cell potential
equal to 0.16 V at 25oC when (OH-) = 0.10 M, (Fe3+)
= 0.50 M and (H2O2) = 0.35 M.
- 2Fe2+(aq) + H2O2(aq)
--> 2Fe3+(aq) + 2OH-(aq)
- Consider the following standard reduction potentials,
half
reaction
|
Eo, V
|
Ni2+(aq)
+ 2e- <==> Ni(s)
|
-0.23
|
Co2+(aq)
+ 2e- <==> Co(s)
|
-0.28
|
Fe2+(aq)
+ 2e- <==> Fe(s)
|
-0.41
|
Cr3+(aq)
+ 3e- <==> Cr(s)
|
-0.74
|
Mn2+(aq)
+ 2e- <==> Mn(s)
|
-1.03
|
- which of the following metals could be used
successfully to galvanize steel?
- Ni only
- Ni and Co
- Fe only
- Mn only
- Mn and Cr
- Consider the following standard reduction potentials,
half
reaction
|
Eo, V
|
Ag+(aq)
+ e- <==> Ag(s)
|
0.800
|
AgI(s)
+ e- <==> Ag(s) + I-(aq)
|
-0.164
|
- Calculate the value of the solubility product
equilibrium constant, Ksp, at 25oC for silver iodide
(AgI).
- AgI(s) <==> Ag+(aq) + I-(aq)
- Which of the following is TRUE for an operating
voltaic cell?
- G
> 0 ; E = 0
- G
< 0 ; E < 0
- G
= 0 ; E > 0
- G
= 0 ; E = 0
- G
< 0 ; E > 0
- Consider the following standard reduction potentials,
half
reaction
|
Eo, V
|
Cu2+(aq)
+ 2e- <==> Cu(s)
|
0.34
|
MnO4-(aq)
+ 2H2O(l) + 3e- <==> MnO2(s) + 4OH-(aq)
|
0.59
|
O2(g) + 2H3O+(aq) + 2e-
<==> H2O2(aq) + 2H2O(l)
|
0.68
|
- and the following redox reactions,
27.i. H2O2(aq) + 2H2O(l)
+ Cu2+(aq) <==> O2<(g) + 2H3O+(aq)
+ Cu(s)
28.
29.ii. 2MnO4-(aq) +
4H2O(l) + 3Cu(s) <==> 3Cu2+(aq) + 2MnO2(s)
+ 8OH-(aq)
30.
31.iii. 2MnO4-(aq) + 10H2O(l)
+ 3H2O2(aq) <==> 3O2(g) + 6H3O+(aq)
+ 2MnO2(s) + 8OH-(aq)
- Which of the redox reactions above will be spontaneous
under standard conditions?
- i only
- ii only
- i and iii
- ii and iii
- None of these.
- In recitation, you saw that silver tarnish (Ag2S(s))
can be converted to silver metal (Ag(s)) by placing the tarnished silver
piece in a dilute solution of baking soda contained in an aluminum pan.
The following half-reactions are thought to be involved,
Ag2S(s)
+ 2H3O+(aq) + 2e- <==> 2Ag(s) + H2S(g)
+ 2H2O(l)
Al3+(aq)
+ 3e- <==> Al(s)
Which of the following statements is
TRUE?
- As the silver piece is being cleaned, H3O+
ions are produced and H2S gas is consumed.
- It is necessary that the silver piece and the aluminum
pan touch so that electrons can be transferred.
- As the silver piece is being cleaned, Al3+
ions in the solution are reduced to Al metal.
- The silver piece being cleaned functions as the anode.
- All of the above are TRUE.
- Calculate the cell potential (in V) at 25oC
for a copper concentration cell in which the Cu2+ concentration
in one half-cell is equal to 0.050 M and the Cu2+ concentration
in the other half-cell is equal to 1.5 M. Note: the number of moles of
electrons transferred is equal to 2.
- Which of the following is a correctly balanced
oxidation/reduction reaction.
- Fe2+ + Au3+ <=> Fe3+
+ Au
- 2 Fe2+ + Au3+ <=> 2 Fe3+
+ Au
- Fe2+ + 3 Au3+ <=> Fe3+
+ 3 Au
- 3 Fe2+ + Au3+ <=> 3 Fe3+
+ Au
- The correct response is not given.
- In acid solution, dichromate ion oxidizes
ferrous iron to ferric iron as illustrated in the partial equation:
Fe2+
+ Cr2O72- <=> Fe3+ + Cr3+
When this equation is balanced, the
right side of the equation will be as follows:
- <=> Fe3+ + 2 Cr3+ + 7 H2O
- <=> 6 Fe3+ + 2 Cr3+ + 7 H2O
- <=> 3 Fe3+ + 2 Cr3+ + 7 H2O
- <=> Fe3+ + 2 Cr3+ + H2O
- The correct response is not given.
- You have observed all of the reactions listed below.
Which of these reactions IS a reduction-oxidation reaction?
- HCl(aq) + H2O(l) --> H3O+(aq)
+ Cl-(aq)
- Fe2O3(s, iron oxide) + 2Al(s)
--> 2Fe(s) + Al2O3(s, aluminum oxide)
- Cu2+(aq) + 4NH3(aq) --> Cu(NH3)42+(aq)
- NH4NO3(s, ammonium nitrate)
--> NH4+(aq) + NO3-(aq)
- None of these is a reduction-oxidation reaction.
- In an electrochemical process called
"electrolysis", H2 gas and O2 gas can be
obtained by passing an electric current through liquid water,
2H2O(l)
--> 2H2(g) + O2(g)
Which species is the OXIDIZING
AGENT and which species is the REDUCING AGENT in this reaction,
respectively?
- H2O(l) ; H2(g)
- O2(g) ; H2O(l)
- H2O(l) ; H2O(l)
- O2(g) ; H2(g)
- H2(g) ; H2O(l)
- In recitation, you saw that silver tarnish (Ag2S(s))
can be converted to silver metal (Ag(s)) by placing the tarnished silver
piece in a dilute solution of baking soda contained in an aluminum pan.
The following half-reactions are involved,
Ag2S(s)
+ 2H3O+(aq) + 2e- --> 2Ag(s) + H2S(g)
+ 2H2O(l)
Al3+(aq)
+ 3e- --> Al(s)
Which of the following is the
correct overall balanced equation for the reaction?
- Ag2S + 2H3O+ + Al
--> 2Ag + H2S + Al3+ + 2H2O
- 6Ag + 3H2S + 6H2O + 2Al3+
--> 2Al + 3Ag2S + 6H3O+
- Ag2S + Al --> Ag + Al3+
- 2Al + 3Ag2S + 6H3O+
--> 6Ag + 3H2S + 6H2O + 2Al3+
- Ag2S + 2H3O+ + Al
--> 2Ag + H2S + 2H2O + Al3+ + e-
- Which of the following statements about porous disks in
voltaic cells is TRUE?
- Free electrons flow through the porous disk to
maintain electrical neutrality in the two half-cells.
- Ions present in the two half-cells flow through the
porous disk to maintain electrical neutrality in both half-cells.
- A porous disk contains a strong electrolyte like
potassium chloride (KCl).
- The wire must be connected directly to the porous disk
in order for the porous disk to be able to maintain electrical neutrality
in the two half-cells.
- In some cases, a porous disk functions as the cathode.
- In the Standard Hydrogen Electrode, a platinum wire is
used as the electrode. Consider the following standard reduction
potentials,
half
reaction
|
Eo, V
|
Zn2+(aq)
+ 2e- --> Zn(s)
|
-0.76
|
2H3O+(aq)
+ 2e- --> 2H2O(l) + H2(g)
|
0.00
|
Pt2+(aq)
+ 2e- --> Pt(s)
|
1.20
|
- Which of the following statements best describes what
would happen if the platinum wire in the Standard Hydrogen Electrode were
replaced with a zinc wire? Note: assume that this is the only change made
to the half-cell.
- Zinc ion in the solution would be reduced; the mass of
the zinc electrode would increase.
- The pH of the solution would decrease.
- The zinc electrode would be oxidized; the mass of the
zinc electrode would decrease.
- This change would have no effect - the Standard
Hydrogen Electrode would continue to function properly.
- It is impossible to tell.
- In recitation, you examined a diagram of a voltaic cell
constructed from zinc and copper in which a tube containing a porous disk
and a solution of KCl was placed in each half-cell (recall, the two tubes
were not connected). Which of the following statements best describes why
this cell has a cell potential of 0.00 V?
- The sum of the zinc and copper half-cell potentials is
equal to 0.00 V.
- Electrical neutrality cannot be maintained in the
half-cells and the KCl tubes.
- All voltaic cells which use zinc in one of the
half-cells have a cell potential of 0.00 V.
- The tubes needed to contain a weak electrolyte, like
AgCl, in order for the cell to function.
- There was not enough information given to solve the
problem.
- Which of the following statements best describes what
will happen when magnesium metal is added to an aqueous solution
containing 1.0 M ferric ion (Fe3+) at 25oC?
half
reaction
|
Eo, V
|
Mg2+(aq)
+ 2e- --> Mg(s)
|
-2.375
|
Fe3+(aq)
+ 3e- --> Fe(s)
|
-0.036
|
- Mg(s) will be oxidized; Fe3+(aq) will be
reduced; the standard cell potential will be 2.339 V.
- Mg(s) will be oxidized; Fe3+(aq) will be
reduced; the standard cell potential will be -2.339 V.
- Fe3+(aq) will be oxidized; Mg(s) will be
reduced; the standard cell potential will be -2.339 V.
- Fe3+(aq) will be oxidized; Mg(s) will be
reduced; the standard cell potential will be 2.339 V.
- There is not enough information given to answer the
question.
- In recitation, you explored the electrochemistry of the
"fruit clock". Which of the following statements best describes
why the clock functions best when citrus fruits (i.e., lemons, oranges,
limes, etc.) are used?
- Citrus fruits work best because they are often
brightly colored.
- Only fruits and vegetables that grow on trees can be
used to power the fruit clock.
- Citrus fruits contain very high concentrations of
copper ion.
- Acid is a product in one of the half-reactions
involved.
- Acid is a reactant in one of the half-reactions
involved.
- Suppose you have been given the task of selecting a
metal to be used as the sacrificial anode for the cathodic protection of a
buried iron fuel tank. Considering the following standard reduction
potentials,
half
reaction
|
Eo, V
|
Pd2+(aq)
+ 2e- --> Pd(s)
|
0.99
|
Ag+(aq)
+ e- --> Ag(s)
|
0.80
|
Cu2+(aq)
+ 2e- --> Cu(s)
|
0.34
|
Ni2+(aq)
+ 2e- --> Ni(s)
|
-0.23
|
Fe2+(aq)
+ 2e- --> Fe(s)
|
-0.41
|
- which of the following metals could be used as the
sacrificial anode in this application?
- Pd
- Ag
- Cu
- Ni
- None of these.
- In lecture, one area of current research in
electrochemistry was described: the development of improved batteries for
use in electric cars. Which of the following properties of batteries are
researchers currently trying to improve?
- range (the number of miles that can be driven before
the batteries must be recharged)
- cost
- lifetime (the number of times the batteries can be
recharged before they must be replaced)
- recharge time (the time required to fully recharge the
batteries)
- Researchers are currently trying to improve all of the
above.
- Use the Standard Reduction Potentials given below to
calculate Kf for Zn(NH3)42+ at
25oC.
Zn2+(aq)
+ 4NH3(aq) <==> Zn(NH3)42+(aq),
Kf = ??
half
reaction
|
Eo, V
|
Zn(NH3)42+(aq)
+ 2e- <==> Zn(s) + 4NH3(aq)
|
-1.04
|
Zn2+(aq)
+ 2e- <==> Zn(s)
|
-0.76
|
- The cell potential for the electrochemical reaction
shown below depends upon the Cl- and Cu2+
concentrations. Calculate the cell potential (in V) at 25oC if
[Cu2+] = 3.5 M and [Cl-] = 1.7 M. Note: the
number of moles of electrons transported in this reaction is equal to 2.
Cu2+(aq)
+ 2Cl-(aq) + 2Ag(s) --> Cu(s) + 2AgCl(s), Eo = 0.12 V
- Consider the following standard reduction potentials,
half
reaction
|
Eo, V
|
I3-(aq) + 2e- --> 3I-(aq)
|
0.53
|
Cr3+(aq)
+ e- --> Cr2+(aq)
|
-0.41
|
- Calculate Go
(in kJ) for the following reaction at 25oC.
- Cr2+(aq) + I3-(aq)
--> Cr3+(aq) + I-(aq)
- In which of the following reactions does the oxidation
number of the sulfur atom NOT CHANGE?
- 3S2- + 8H+ + 2NO3-
(nitrate ion) --> 2NO + 3S + 4H2O
- 2SO2 (sulfur dioxide) + O2
--> 2SO3 (sulfur trioxide)
- 2H2S + 3O2 --> 2SO2
(sulfur dioxide) + 2H2O
- S8 + 8O2 --> 8SO2
(sulfur dioxide)
- SO2 (sulfur dioxide) + H2O
--> H2SO3 (sulfurous acid)
- Which of the following reactions IS a
reduction-oxidation reaction?
- NH3(aq) + H2O(l) --> NH4+(aq)
+ OH-(aq)
- Cu2+(aq) + 4NH3(aq) --> Cu(NH3)42+(aq)
- AgF(s) --> Ag+(aq) + F-(aq)
- 2Cu+(aq) --> Cu2+(aq) + Cu(s)
- 2NO2(g, nitrogen dioxide) --> N2O4(g,
dinitrogen tetroxide)
- Which of the following statements explains why a
definition of standard state conditions is needed in electrochemistry?
- Cell potentials vary with concentration.
- Cell potentials vary with temperature.
- Cell potentials vary with partial pressures of gases.
- Responses (a) and (c) are correct.
- Responses (a), (b) and (c) are all correct.
- Consider the following reaction and standard cell
potential,
Ni2+(aq)
+ 6NH3(aq) --> Ni(NH3)62+(aq), Eo
= +0.25 V
Which of the following best
describes what would happen in a solution that initially contains 1.0 M Ni2+,
0.01 M NH3 and 6.0 M Ni(NH3)62+ at
25oC? (Assume that the number of moles of electrons transported in
this reaction is equal to 2.)
- The concentrations of both Ni2+ and NH3
would decrease and the concentration of Ni(NH3)62+
would increase.
- The concentrations of both Ni2+ and NH3
would increase and the concentration of Ni(NH3)62+
would decrease.
- The concentration of Ni(NH3)62+
would decrease, the concentration of NH3 would increase and
the concentration of Ni2+ would remain the same.
- The concentrations of Ni2+, NH3
and Ni(NH3)62+ would all remain the
same.
- It is impossible to tell.
- Consider the following standard reduction potentials,
half
reaction
|
Eo, V
|
Ca2+
+ 2e- --> Ca
|
-2.76
|
Pb2+
+ 2e- --> Pb
|
-0.13
|
Cu2+
+ 2e- --> Cu
|
+0.34
|
Hg22+
+ 2e- --> Hg
|
+0.80
|
Pt2+
+ 2e- --> Pt
|
+1.20
|
- Which of the following metals is the strongest REDUCING
AGENT?
- Ca
- Pb
- Cu
- Hg
- Pt
- Consider the following standard reduction potentials,
half
reaction
|
Eo, V
|
Fe2+
+ 2e- --> Fe
|
-0.4090
|
Ag+
+ e- --> Ag
|
0.7996
|
O2 + 2H2O + 4e- -->
4OH-
|
+0.4010
|
- Which of the following statements best describes what
would happen if a block of silver metal were connected to a buried iron
pipe via a wire (i.e., as in a cathodic protection process).
- The silver metal would corrode, a current would be
produced in the wire, and O2 would be reduced on the surface
of the iron pipe.
- The silver metal would corrode, a current would be
produced in the wire, and Fe2+ would be reduced on the surface
of the iron pipe.
- The iron pipe would corrode, a current would be
produced in the wire, and Ag+ would be reduced on the surface
of the silver metal.
- The iron pipe would corrode, no current would be
produced in the wire, and O2 would be reduced on the surface
of the iron pipe.
- Neither the iron pipe nor the silver metal would be
oxidized but O2 would be reduced.
- Consider the following reduction-oxidation reaction,
Zn(s)
+ Cu2+(aq) --> Cu(s) + Zn2+(aq), Eo = +1.10
V
When the components of the two
half-reactions involved in this reaction are correctly separated, this reaction
can be used to do electrical work and the change in internal energy of the
system decreases. Which of the following statements best describes what will
happen if Zn(s) is added to a solution containing Cu2+(aq) at
constant volume at 25oC?
- The reaction will occur and the temperature of the
solution will increase.
- The reaction will occur and the temperature of the
solution will decrease.
- The reaction will occur and the temperature of the
solution will remain the same.
- The reaction will not occur and the temperature of the
solution will remain the same.
- The reaction will not occur but the temperature of the
solution will increase.
- Using the following standard reduction potentials,
half
reaction
|
Eo, V
|
Cl2
+ 2e- --> 2Cl-
|
+1.36
|
Cr3+
+ 3e- --> Cr
|
-0.74
|
- calculate Go
(in kJ) for the reaction,
- 3Cl2 + 2Cr --> 6Cl- + 2Cr3+
- Use the following information to answer the next four
(4) questions.
- A galvanic cell is constructed from a half cell
containing a solid copper electrode in 1.0 M Cu(NO3)2
solution and a half cell containing a solid aluminum electrode in 1.0 M
Al(NO3)3 solution at standard conditions. The half
cells are linked by an external circuit and by a KCl salt bridge.
- The balanced overall (net) cell reaction for a
spontaneous process is:
- Cu(s) + Al3+(aq) --> Cu2+(aq)
+ Al(s)
- 3 Cu(s) + 2 Al3+(aq) --> 3 Cu2+(aq)
+ 2 Al(s)
- 3 Cu2+(aq) + 2 Al(s) --> 3 Cu(s) + 2 Al3+(aq)
- Cu2+(aq) + Al(s) --> Cu(s) + Al3+(aq)
- The reaction is not spontaneous.
- Which of the following statements is TRUE about this
cell?
- The aluminum electrode is the anode; the copper
electrode is the cathode.
- The electrons flow from the copper electrode to the
aluminum electrode.
- The cell diagram is |Cu solid|Cu2+, 1.0
M|salt bridge|Al solid|Al3+, 1.0 M|
- G
is greater than zero.
- S
is the driving force of this reaction.
- This cell generates a standard potential of:
- +1.32 V
- -2.00 V
- -1.32 V
- +2.00 V
- The cell is at equilibrium.
- An expression for the equilibrium constant of this
reaction at 25oC is:
- e205
- e298
- e467
- e831
- e965
- You have installed a new hot water heater in your
house, and you notice that the iron tank has a large metal bar bolted to
it on the inside. You conclude that this bar is a sacrificial anode and
that it could be made of:
- Ag
- Ni
- Pb
- Sn
- Mg
- We used copper and zinc electrodes stuck in an apple to
run a small clock. Which of the following statements must be TRUE?
- The zinc strip was the anode.
- The apple was the salt bridge.
- Ecell > 0.
- G
< 0.
- All of these statements are true.