CHM1
Review Exam 12
Topics – REDOX
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REDOX Reactions
• Oxidation
• Reduction
• Oxidizing agent
• Reducing agent
Galvanic (Voltaic) Cells
• Anode
• Cathode
• Salt bridge
• Electrolyte
• Half-reactions
• Voltage
o Positive voltages are due to spontaneous REDOX reactions
o Negative voltages are due to nonspontaeous REDOX reactions
Electrolysis Cells
• Applying a more positive electrical potential to a cell with negative voltage can cause a
nonspontaeous REDOX cell to become spontaneous.
o Water
o Electroplating
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Multiple Choice
1. Given the reaction
2 Al (s) + Fe2O3 (s)  Al2O3 (s) + 2 Fe (s)
Which species undergoes reduction?
(1) Al
(2) Fe
(3) Al3+
(4) Fe3+
2. Which energy transformation occurs when an electrolytic cell is in operation?
(1) chemical energy  electrical energy
(2) electrical energy  chemical energy
(3) light energy  heat energy
(4) light energy  chemical energy
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3. Given the reaction
Mg (s) + 2 AgNO3 (aq)  Mg(NO3)2 (aq) + 2 Ag (s)
Which type of reaction is a REDOX reaction?
(1) single replacement
(2) double replacement
4.
(3) synthesis
(4) decomposition
Which equation shows conservation of both mass and charge?
(1) Cl2 + Br-  Cl- + Br2
(2) Cu + 2 Ag+  Cu2+ + Ag
(3) Zn + Cr3+  Zn2+ + Cr
(4) Ni + Pb2+  Ni2+ + Pb
5. The diagram below shows a key being plated with copper in an electrolytic cell.
Given the reduction reaction for this cell:
Cu2+ (aq) + 2 e-  Cu (s)
This reduction occurs at
(1) A, which is the anode
(2) A, which is the cathode
(3) B, which is the anode
(4) B, which is the cathode
6. What is conserved during a chemical reaction?
(1) mass, only
(2) charge, only
(3) both mass and charge
(4) neither mass nor charge
CHM1
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7. Which type of reaction occurs when nonmetal atoms become negative nonmetal ions?
(1) oxidation
(2) reduction
(3) substitution
(4) condensation
8. Given the reaction:
Zn (s) + 2 HCl (aq)  ZnCl2 (aq) + H2
Which statement correctly describes what occurs when this reaction takes place in a
closed system?
(1) Atoms of Zn (s) lose electrons and are oxidized.
(2) Atoms of Zn (s) lose electrons and are reduced.
(3) There is a net loss of mass.
(4) There is a net gain of mass.
9. A voltaic (Galvanic) cell differs from an electrolytic cell in that in a voltaic cell
(1) energy is produced when the reaction occurs
(2) energy is required for the reaction to occur
(3) both oxidation and reduction occur
(4) neither oxidation nor reduction occur
10. What is the purpose of the salt bridge in a voltaic cell?
(1) It blocks the flow of electrons
(2) It blocks the flow of positive and negative ions.
(3) It is a path for the flow of electrons.
(4) It is a path for the flow of positive and negative ions.
11. How many electrons must be removed from elemental hydrogen (H2) to produce two
moles of hydrogen ions (H+) in an aqueous solution (6.02 x 1023 electrons per 1
mole)?
(1) 6.02 x 1023
(2) 12.04 x 1023
(3) 3.01 x 1023
(4) none of the above
12. Which statement is true for any electrochemical cell?
(1) Oxidation occurs at the anode, only.
(2) Reduction occurs at the anode, only.
(3) Oxidation occurs at both the anode and the cathode.
(4) Reduction occurs at both the anode and the cathode.
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Review for Exam 10
13. Given the equation:
2 Al + 3 Cu2+  2 Al3+ + 3 Cu
The reduction half reaction is
(1) Al  Al3+ + 3 e- (3) Al + 3 e-  Al3+
(2) Cu2+ + 2 e-  Cu (4) Cu2+  Cu + 2 e14. A diagram of a electrochemical cell and an equation are shown below.
When the switch is closed, the electrons will flow from
(1) the Pb (s) to the Cu (s)
(2) the Cu (s) to the Pb (s)
(3) the Pb2+ (aq) to the Pb (s)
(4) the Cu2+ (aq) to the Cu (s)
15. When a neutral atom undergoes oxidation, the atom’s oxidation state
(1) decreases as it gains electrons
(2) decreases as it loses electrons
(3) increases as it gains electrons
(4) increases as it loses electrons
16. Given the equation:
C (s) + H2O (g)  CO (g) + H2 (g)
Which species undergoes reduction?
(1) C (s)
(2) H+
(3) C2+
(4) H2 (g)
CHM1
Review for Exam 10
17. Given:
Mg (s) + 2 H+ (aq) + 2 Cl- (aq) --> Mg2+ (aq) + 2 Cl- (aq) + H2 (g)
Which species undergoes oxidation?
(1) Mg (s)
(2) H+ (aq)
(3) Cl- (aq)
(4) H2 (g)
18. Which particles are gained and lost during a redox reaction?
(1) electrons
(2) protons
(3) neutrons
(4) positrons
19. What is the oxidation number of chromium in K2Cr2O7?
(1) 12+
(2) 2+
(3) 3+
(4) 6+
20. What is the oxidation number of manganese in MnO4-?
(1) -1
(2) 4-
(3) 5+
(4) 7+
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Short Answer
Base your answers to the following questions on the diagram of the voltaic cell below.
21. When the switch is closed, in which half-cell does oxidation occur?
22. When the switch is closed, state the direction that electrons will flow through the
wire.
23. Based on the given equation, write the balanced half-reaction that occurs in half-cell
1.
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Review for Exam 10
24. If, Ag+ (aq) + e-  Ag (s), E° = +0.799 V and, Zn2+ (aq) + 2 e-  Zn (s), E° = –0.63
V, what is the standard potential of the cell shown below. Explain.
KNO3
Ag (s)
Salt bridge
Ag+ (aq)
Zn (s)
Zn2+ (aq)
2 Ag+ (aq) + Zn (s)  2 Ag (s) + Zn2+ (aq)
25. Define the following
(a) Oxidation
(b) oxidizing agent
(c) salt bridge
(d) anode
(e) electrolysis
CHM1
Review for Exam 10
Answers
1. 4
2. 2
3. 1
4. 4
5. 2
6. 3
7. 2
8. 1
9. 1
10. 4
11. 2
12. 1
13. 2
14. 1
15. 4
16. 2
17. 1
18. 1
19. 4
20. 4
21. Oxidation occurs at the anode, which in this case is the compartment containing the
Pb electrode.
22. FAT CAT from the anode to the cathode, or from the Pb electrode to the Ag
electrode.
23. Pb (s)  Pb2+ (aq) + 2 e24. ince the Ag+ is reduced with a potential of +0.799 V and the Zn is oxidized with a
potential of +0.63 V the overall REDOX potential is 1.43 V. The reaction is
spontaneous.
25. (a) oxidation is the lose of electrons; (b) the oxidizing agent is the species that gets
reduced; (c) The salt bridge conducts ions between the anode and cathode; (d) The
anode is the electrode where oxidation occurs; (e) electrolysis is a redox process in
which electrical potential energey is used to cause a nonspontaneous redox reaction to
become spontaneous.