254 ❯ STEP 4. Review the Knowledge You Need to Score High
- Co2+ + 2 e- → Co E° = –0.28 V
Cd^2 + + 2 e- → Cd E° = –0.40 V
Given the above standard reduction potentials,
estimate the approximate value of the equilib-
rium constant for the following reaction:
Cd + Co^2 + → Cd^2 + + Co
(A) 10-^4
(B) 10-^2
(C) 10^4
(D) 10^16- A sample of silver is to be purified by electro-
refining. This will separate the silver from an
impurity of gold. The impure silver is made into
an electrode. Which of the following is the best
way to set up the electrolytic cell?
(A) an impure silver cathode and an inert anode
(B) an impure silver cathode and a pure gold
anode
(C) a pure silver cathode with an impure silver
anode
(D) a pure gold cathode with an impure silver
anode - 2 Fe^3 + + Zn → Zn^2 + + 2 Fe^2 +
The reaction shown above was used in an electro-
lytic cell. The voltage measured for the cell was
not equal to the calculated E° for the cell. Which
of the following could cause this discrepancy?
(A) The anion in the anode compartment was
chloride instead of nitrate, as in the cathode
compartment.
(B) One or more of the ion concentrations was
not 1 M.
(C) Both solutions were at 25°C instead of 0°C.
(D) The solution in the salt bridge was Na 2 SO 4
instead of KNO 3.
- How many grams of mercury could be produced
by electrolyzing a 1.0 M Hg(NO 3 ) 2 solution with
a current of 2.00 A for 3.00 h?
(A) 22.4 g
(B) 201 g
(C) 11.2 g
(D) 44.8 g
12. An electrolysis cell was constructed with two
platinum electrodes in a 1.00 M aqueous solution
of KCl. An odorless gas evolves from one elec-
trode, and a gas with a distinctive odor evolves
from the other electrode. Choose the correct
statement from the following list.
(A) The gas with the distinctive odor was evolved
at the anode.
(B) The odorless gas was oxygen.
(C) The gas with the distinctive odor was evolved
at the cathode.
(D) The odorless gas was evolved at the anode.
13. 2 BrO 3 - (aq) + 12 H+(aq) + 10 e- → Br 2 (aq) +
6 H 2 O(l)
Which of the following statements is correct for
the above reaction?
(A) The BrO 3 - undergoes oxidation at the anode.
(B) Br goes from a –1 oxidation to a 0-oxidation
state.
(C) Br 2 is oxidized at the anode.
(D) The BrO 3 - undergoes reduction at the
cathode.
14. 2 M(s) + 3 Zn^2 +(aq) → 2 M^3 +(aq) + 3 Zn^2 +(aq)
E ° = 0.90 V
Zn^2 +(aq) + 2e- → Zn(s) E ° = –0.76 V
Using the above information, determine the
standard reduction potential for the following
reaction: M^3 +(aq) + 3 e- → M(s).
(A) 0.90 V
(B) –1.66 V
(C) 0.00 V
(D) –0.62 V
15. 2 SO 42 - (aq) + 10 H+(aq) + 8 e- → S 2 O 32 - (aq) +
5 H 2 O(l)
A chemistry student constructs a voltaic cell. The
above half-reaction occurs in one of the cell com-
partments. Which of the following statements is
true concerning this half-reaction?
(A) The sulfur undergoes oxidation.
(B) This half-reaction occurs at the cathode.
(C) The oxidation state of sulfur does not change.
(D) The H+ serves as a catalyst.