I. Multiple Choice. (96 points) Select the best response for each of the following and record your answers on the Scantron. Do not erase; erasures may result in a misgrading of your response.
1. Which one of the
following changes requires an oxidizing agent?
b. O2- ® H2O
c. H+ ® H2
d. Zn2+ ® Zn
e. Fe3+ ® Fe2+
2. For the cell reaction, O2 + 4 H+ + 2 Cu
® 2 Cu2+ + 2 H2O, the E° = 0.89 V. Which one of the following changes will increase the potential of the cell?a. increase the pH
b. decrease the concentration of the Cu2+
c. decrease the partial pressure of O2
d. increase the size of the copper anode
e. increase the size of the platinum cathode
3. For the voltaic cell, Zn|Zn2+||Fe3+,
Fe2+|C(gr), one of the following statements is false. Which one?
a. The electrons flow from zinc to graphite
b. The anode itself is oxidized
c. Zn2+ flows toward the graphite electrode
d. Fe2+ is reduced at the graphite electrode
e. The reducing agent in the cell is the zinc electrode
4. In an electrolytic cell, electrons flow from ______ and cations
flow toward the ________.
a. anode to cathode, positive electrode
b. anode to cathode, anode
c. cathode to anode, cathode
d. anode to cathode, negative electrode
e. cathode to anode, positive electrode
5. All of the above complexes have the same ligands and same metal
ion. Identify two isomers that are optical isomers (enantiomers).
a. a and b
b. a and d
c. c and d
d. c and e
e. b and e
6. In the dry cell,
a. the zinc electrode is the oxidizing agent
b. electrons flow from the graphite electrode to the zinc electrode
c. the electrolyte is MnO2
d. the reducing agent is MnO2
e. the graphite electrode is the cathode
7. Consider the following half-reactions:
MnO4- + 8 H+ + 5 e- ® Mn2+ + 4 H2O E° = +1.51 V
Fe3+ + e- ® Fe2+
E° = +0.77 V
Pb2+ + 2 e- ® Pb
E° = –0.13 V
Al3+ + 3 e- ® Al
E° = –1.66 V
Identify the correct statement
a. Fe3+ will oxidize Mn2+
b. Pb metal is a stronger reducing agent than is Al metal
c. Al metal is the strongest oxidizing agent of those listed
d. Fe3+ is a stronger oxidizing agent than is Pb2+
e. Al3+ reacts with any metal or ion above Al in the table
8. In the discharge of the lead-acid (automobile) battery,
a. the cell reaction has a potential of about 2 V
b. the anode is constructed of lead
c. the oxidizing agent is PbO2
d. PbSO4 forms at both the anode and the cathode
e. all of the above statements are true
9. The industrial process used for the production of active
metals such as sodium and magnesium is
a. mining
b. electrolysis of an aqueous salt solution
c. a mixture of an oxidizing agent with a reducing agent
d. electrolytic refining
e. electrolysis of a molten salt
10. An electrolytic cell equipped with copper electrodes is used to
electrolyze an aqueous CuCl2 solution. Which is the most likely reaction
occurring at the cathode?
a. H2O
b. H2O ® O2, H+
c. Cu2+ ® Cu
d. Cl- ® Cl2
e. Cl2 ® Cl-
11. When an aqueous solution of sodium sulfate is electrolyzed,
a gas is evolved at the cathode. The gas is
a. oxygen
b. nitrogen
c. hydrogen
d. sulfur dioxide
e. sulfur trioxide
12. For the coordination compound, K2[Co(CN)4(en)],
the coordination number and the oxidation state of the metal ion of the complex are
respectively
a. 5 and 3+
b. 5 and 2-
c. 5 and 2+
d. 6 and 2+
e. 6 and 3+
13. The two complexes of [PtCl2Br2]2-
are
a. square planar, anionic, and geometric isomers
b. square planar, anionic, and linkage isomers
c. tetrahedral, cationic, and geometric isomers
d. square planar, cationic, and geometric isomers
e. square planar, anionic, and optical isomers
14. For the voltaic cell, Fe|Fe3+||Cl-|Cl2|Pt
a. Fe3+ is oxidized at the Fe electrode
b. Cl2 is produced at the Pt electrode
c. Cl- is reduced at the Pt electrode
d. Cl2 is reduced at the Pt electrode
e. Fe3+ is reduced at the Fe electrode
15. The number of moles of AgCl that precipitates from the reaction
of [CoCl(NH3)5]Cl2 and an excess of AgNO3 is
a. 0
b. 1
c. 2
d. 3
e. not enough information
II. Exercises. (69 points) Complete the following exercises in the space provided. Your organized and chemically logical (neat) work must be shown; correct answers only account for 10% of the credit indicated.
1. (10 points) An aqueous solution of K2CrO4
is used for electroplating chromium metal. How many hours will it take to
electroplate 25.0 g of chromium metal onto an automobile grill using a current of
15.0 amperes.
5.15 hours
2. (24 points) Consider a voltaic cell constructed from the two redox
couples.
Sn4+ + 2 e-
Cd2+ + 2 e- ® Cd E° = –0.40 V
a. (10 pts) Write the cell notation for the cell
Cd | Cd2+ || Sn4+,Sn2+ | Pt
b. (6 pts) The direction of electron flow is from the
(specify metal) _cadmium____ electrode to the (metal) __platinum___ electrode.
c. (3 pts) The Sn2+ ions flow toward the (specify metal) __cadmium_____ electrode.
d. (5 pts) Calculate the standard free energy change, DG°, for the voltaic cell.
DG° = -106 kJ
3. (35 points) A voltaic cell was constructed from the following two half-reactions:
NO3- (0.010 M) + 4 H+ (pH = 2.0) + 3 e-
Ag+ (0.0060 M) + e- ® Ag E° = +0.80 V
a. (10 pts) Write the balanced cell reaction. (Hint: write the cathodic and anodic half-reactions as they occur in the voltaic cell.)
NO3- + 4 H+ + 3 Ag ® NO + 2 H2O + 3 Ag+
b. (5 pts) What is the standard cell potential?
E° = 0.16 V
c. (15 pts) What is the actual cell potential?
E = 0.094 V
d. (5 pts) What is the equilibrium constant for the cell reaction?
K = 1.3 x 108