1. No category

Name __________________________________
Period ______
Homework Packet – Unit 6
1. What is the oxidation state of arsenic in
H3AsO3?
(A) +1
(B) +3
(C) +5
(D) –3
(E) –5
2. In the reaction
SO2(g) + 2H2S(g) → 3S(s) + 2H2O(l)
(A) S is oxidized and H is reduced
(B) S is reduced and there is no oxidation
(C) S is reduced and H is oxidized
(D) S is both reduced and oxidized
3. 3Cu(s) + 2NO3–(aq) + 8H+(aq) →
3Cu2+(aq) + 2NO(g) + 4H2O(l)
True statements about the reaction
represented above include which of the
following?
I. Cu(s) acts as an oxidizing agent.
II. The oxidation state of nitrogen
changes from +5 to +2.
III. Hydrogen ions are oxidized to form
H2O(l).
(A) I only
(B) II only
(C) III only
(D) I and II
(E) II and III
4. When the reaction below is balanced, what
is the coefficient for H+?
_MnO4–(aq) + _NO2–(aq) + _H+(aq) →
_MnO2(s) + _NO3–(aq) + _H2O(l)
(A) 1
(B) 2
(C) 4
(D) 6
(E) 8
5. Which ion can be oxidized by appropriate
chemical means but also can be reduced by a
different chemical reaction?
(A) Fe2+
(B) F–
(C) CO32–
(D) NO3–
6. Which of the following occurs in this
reaction?
AlF63–(aq) + 3e– → Al(s) + 6F–(aq)
(A) AlF63– is reduced at the cathode.
(B) Al is oxidized at the anode.
(C) Aluminum is converted from the –3
oxidation state to the 0 oxidation state.
(D) F– acts as a reducing agent.
(E) F– is reduced at the cathode.
7. What is the potential in a voltaic cell for the
spontaneous reaction between the Ag/Ag+
and Zn/Zn2+ half–cells?
Zn2+ + 2e– → Zn, E = –0.763 V
Ag+ + e– → Ag, E = +0.799 V
(A) –2.361 V
(B) –1.562 V
(C) +1.562 V
(D) +2.361 V
8. Given the following standard electrode
potentials,
Ni2+ + 2e– → Ni(s)
E = –0.23 V
3+
–
Cr + 3e → Cr(s)
E = –0.74 V
which pair of substances will react
spontaneously?
(A) Ni2+ with Cr3+
(B) Ni with Cr3+
(C) Ni2+ with Cr
(D) Ni with Cr
9. The oxidation of the metal M is shown in
the following half reaction:
M3+(aq) + 3e– → M(s)
According to the information shown in the
two reactions below, what is the standard
reduction potential for the half reaction
shown above?
M(s) + 3Ag+(aq) → 3Ag(s) + M3+(aq)
E° = +2.46 V
Ag+(aq) + e– → Ag(s) E° = +0.80 V
(A) –0.06 V
(B) +0.06 V
(C) +1.66 V
(D) +3.26 V
(E) –1.66 V
10. The standard reduction potential for Fe2+ is
–0.44 V and for Ag+ it is +0.80 V.
Determine the value of E°cell for a voltaic
cell in which the overall reaction is
Fe(s) + 2Ag+(aq) → Fe2+(aq) + 2Ag(s)
(A) 0.36 V
(B) 1.16 V
(C) 1.24 V
(D) 2.04 V
(E) 1.68 V
Use the diagram shown above for the next two
questions. The standard reduction potential for
Ni2+ is –0.28 V and for Ag+ it is +0.80 V.
11. The standard reduction potential for Pb2+ is
–0.13 V and for Ni2+ it is –0.28 V. In a
voltaic cell, the reduction reaction occurs at
the ____ electrode. This electrode is called
the____.
(A) Pb, cathode
(B) Pb, anode
(C) Ni, cathode
(D) Ni, anode
(E) no reduction will occur because the
reaction is nonspontaneous.
12. The oxidizing agent in a cell based on nickel
and silver is
(A) Ni
(B) Ni2+
(C) Ag+
(D) Ag
(E) the salt bridge
13. Electrons in the cell flow through the ___
toward the ___.
(A) wire, silver electrode
(B) wire, nickel electrode
(C) salt bridge, nickel electrode
(D) salt bridge, silver electrode
(E) salt bridge, voltmeter
14. A galvanic cell is constructed using a chromium electrode
in a 1.00 M solution of Cr(NO3)3 and a copper electrode
in a 1.00 M solution of Cu(NO3)2. Both solutions are at
25˚C. A partial diagram of the cell is shown here.
a) Write a balanced net ionic equation for the spontaneous reaction that occurs as the cell operates.
Identify the oxidizing agent and the reducing agent.
Cu
Cr
b) Which metal is the cathode?
1 M Cr(NO3)3
c) What additional component is necessary to make the cell operate?
d) What function does the component identified in (c) serve?
2
1 M Cu(NO3)2
15. Describe what you would see if you added a piece of metal to acid as described below. Write
balanced equations for any reactions that occur.
a) A piece of zinc metal to a test tube that contains 6 M hydrochloric acid.
b) A piece of copper metal to another test tube that contains 6 M hydrochloric acid.
c) Explain how you used the table of standard reduction potentials to predict the observed results.
d) In a separate experiment, concentrated nitric acid is added to a test tube containing a piece of
copper metal. Describe what you would see.
e) Explain any differences between the results obtained in the experiment of part (d) and those
obtained with copper metal in part (b).
16. Cu(s) + 2Ag+(aq) → Cu2+(aq) + 2Ag(s)
If the equilibrium constant for the reaction above is 3.7 x 1015, which of the following correctly
describes the standard voltage, E°, and the standard free energy change, ΔG°, for this reaction?
(A) E° is positive and ΔG° is negative.
(B) E° is negative and ΔG° is positive.
(C) E° and ΔG° are both positive.
(D) E° and ΔG° are both negative.
(E) E° and ΔG° are both zero
17. Given the following standard electrode potentials:
E = 0.337 V
Cu2+ + 2e– → Cu(s)
3+
–
Al + 3e → Al(s)
E = –1.66 V
the voltage of the cell: Al2(SO4)3 (0.1 M) / Al // Cu / CuSO4 (0.5 M) would be:
(A) 0.00V
(B) 0.72 V
(C) 2.00 V
(D) 5.70 V
18. What is [Cu2+] in the cell Zn / Zn2+ (0.05 M) // Cu2+ (? M) / Cu if the cell voltage is 1.03 V?
(A) 0.12 M
(B) 0.0002 M
(C) 0.05 M
(D) 0.0035 M
3
19. A voltaic cell is designed using the following reaction: Zn(s) + 2Ag+(aq) → Zn2+(aq) + 2Ag(s)
a) Determine the standard voltage Ecell for this reaction.
b) Suppose the concentration of Zn2+ in the Zn/Zn2+ half–cell is maintained at 1.00 M. Excess
hydrochloric acid is added to the Ag/Ag+ half cell, precipitating AgCl(s) and making the
concentration of Cl– = 0.100 M. Under these conditions, the cell voltage is found to be 1.04 V.
Calculate the concentration of Ag+ in the Ag/Ag+ half–cell.
20. An electrochemical cell consists of a nickel electrode in an acidic solution of 1.00 M Ni(NO3)2
connected by a salt bridge to a second component with an aluminum electrode in an acidic solution
of 1.00 M AlCl3.
a) Write an equation for the half–cell reaction occurring at each electrode. Indicate whether each
reaction occurs at the anode or the cathode.
b) Write a net ionic equation for the overall spontaneous cell reaction that occurs when the circuit is
complete. Calculate the standard voltage Ecell for this reaction.
c) Calculate the change in voltage when the cell described above has initial concentrations of 0.500
M Ni(NO3)2 and 0.750 M AlCl3.
21. E = 1.101 V at 25C for the reaction of a metal with copper ion is:
M(s) + Cu2+(aq) → M2+(aq) + Cu(s)
a) Determine the standard electrode potential for the reduction half–reaction:
M2+(aq) + 2e– → M(s)
b) A cell is constructed in which the reaction above occurs. All substances are initially in their
standard states and equal volumes of the solutions are used. The cell is then discharged.
Calculate the value of the cell potential E when [Cu2+] drops to 0.20 M.
4
The spontaneous reaction that occurs when this cell
operates is:
2Ag+(aq) + Cd(s) → 2Ag(s) + Cd2+(aq)
Select A – E below for the next four problems.
(A) Voltage increases.
(B) Voltage decreases.
(C) Voltage becomes zero and remains at zero.
(D) No change in voltage occurs.
(E) Direction of voltage change cannot be predicted
without additional information.
Which of the above occurs for each of the following circumstances?
22. A 50 mL sample of a 2 M Cd(NO3)2 solution is added to the beaker on the left.
23. The silver electrode is made larger.
24. The salt bridge is replaced by a platinum wire.
25. Current is allowed to flow for 5 minutes
26. If 0.060 faraday is passed through an electrolytic cell containing a solution of In3+ ions, the
maximum number of moles of In that could be deposited at the cathode is
(A) 0.010 mole
(B) 0.020 mole
(C) 0.030 mole
(D) 0.060 mole
(E) 0.18 mole
27. A direct-current power supply of low voltage (less than 10 volts) has lost the markings that indicate
which output terminal is positive and which is negative. A chemist suggests that the power supply
terminals be connected to a pair of platinum electrodes that dip into a 0.1 M KI solution. Which of
the following correctly identifies the polarities of the power supply terminals?
(A) A gas will be evolved only at the positive electrode.
(B) A gas will be evolved only at the negative electrode.
(C) A brown color will appear in the solution near the negative electrode.
(D) A metal will be deposited on the positive electrode.
(E) None of the methods above will identify the polarities of the power supply terminals.
28. In the electroplating of nickel, 0.200 faraday of electrical charge is passed through a solution of
NiSO4. What mass of nickel is deposited?
(A) 2.94 g
(B) 5.87 g
(C) 11.7 g
(D) 58.7 g
(E) 294 g
5
29. In the reaction AlF63– + 3e– → Al + 6F–, A steady current of 10 amperes in passed though an
aluminum-production cell for 15 minutes. Which of the following is the correct expression for
calculating the number of grams of aluminum produced? (1 faraday = 96,500 coulombs)
10 x 15 x 96500
(A)
g
27 x 60
10 x 15 x 27
(B) 60 x 96500 g
10 x 15 x 60 x 27
(C)
g
96500 x 3
96500 x 27
(D) 10 x 15 x 60 x 3 g
27 x 3
(E) 96500 x 10 x 15 x 60 g
30. A solution of an unknown metal nitrate, M(NO3)2, is electrolyzed.
a) When a constant current of 2.50 amperes is applied for 35.0 minutes, 3.06 grams of the metal M
is deposited. Calculate the molar mass of M and identify the metal.
b) The metal identified in (a) is used with zinc to construct a galvanic cell, as shown below. Write
the net ionic equation for the cell reaction and calculate the cell potential, E°cell.
K
M etal
M
1.0 M M(NO3)2
+
Cl Zinc
1.0 M ZnSO4
c) Calculate the value of the standard free energy change ∆G° at 25˚C for the reaction in (b).
d) Calculate the potential E for the cell shown in (b) if the initial concentration of ZnSO4 is 0.10 M
but the concentration of the M(NO3)2 solution remains unchanged.
6
31. 10 amperes are passed through molten aluminum chloride for 5.5 hours. How many grams of
aluminum metal could be produced by this electrolysis?
(A) 18.5 g
(B) 55.4 g
(C) 91.2 g
(D) 273 g
32. In the electroplating of silver from cyanide solution, the reaction at the cathode is:
Ag(CN)2–(aq) + e– → Ag(s) + 2CN–(aq)
How many grams of silver should be deposited by a current of 4.5 A in 28.0 minutes?
(A) 0.141 g
(B) 4.23 g
(C) 8.45 g
(D) 12.53 g
33. Aluminum oxide may be electrolyzed at 1000C to furnish aluminum metal. The cathode reaction is:
Al3+ + 3e– → Al
To prepare 5.12 kg of aluminum metal by this method would require how many coulombs of
electricity?
(A) 5.49 x 107 C
(B) 1.83 x 107 C
(C) 5.49 x 104 C
(D) 54.9 C
34. The electrolysis of molten sodium chloride is carried out in an electrochemical cell.
a) Write the balanced half–cell reactions that occur at each electrode, indicating whether each takes
place at the anode or cathode.
b) If a current of 1.06 A is used, how long will it take to produce 1.00 L of Cl2(g) at 24 C and
742 mm Hg?
c) Calculate G for this system.
7
35. Explain each of the following.
a) When an aqueous solution of NaCl is electrolyzed, Cl2(g) is produced at the anode, but no Na(s)
is produced at the cathode.
b) The mass of Fe(s) produced when 1 faraday is used to reduce a solution of FeSO4 is 1.5 times the
mass of Fe(s) produced when 1 faraday is used to reduce a solution of FeCl3.
([Pb2+] = [Zn2+] = 1 M)
c) Zn(s) + Pb2+(aq) → Zn2+(aq) + Pb(s)
The cell that utilizes the reaction above has a higher potential when [Zn2+] is decreased and
[Pb2+] is held constant, but a lower potential when [Pb2+] is decreased and [Zn2+] is held
constant.
d) The cell that utilizes the reaction given in (c) has the same cell potential as another cell in which
[Zn2+] and [Pb2+] are each 0.1 M.
36. Titanium can be reduced in an acid solution from TiO2+(aq) to Ti3+(aq) with zinc metal.
a) Write a balanced equation for the reaction of TiO2+(aq) with zinc in acid solution.
b) What mass of zinc metal is required for the complete reduction of a 50.00 mL sample of a
0.115 M solution of TiO2+(aq)?
c) Alternatively, the reduction of TiO2+(aq) to Ti3+(aq) can be carried out electrochemically. What
is the minimum time, in seconds, required to reduce another 50.00 mL sample of the
0.115 M TiO2+(aq) solution with a direct current of 1.06 amperes?
d) The standard reduction potential E° for TiO2+(aq) to Ti3+(aq) is +0.060 V. The standard
reduction potential E° for Zn2+(aq) to Zn(s) is –0.763 V. Calculate the standard cell potential
E°cell and the standard free energy change ∆G° for the reaction described in part (a).
8