,CHEM 104 Module 4 Exam General Chemistry II
w/Lab | Portage | 26/27|Q&A Actual (PDF)
1. Which statement correctly defines oxidation in the context of electron transfer?
A) Gain of electrons, resulting in a decrease in oxidation number.
B) Loss of electrons, resulting in an increase in oxidation number.
C) Gain of protons, resulting in a decrease in pH.
D) Loss of oxygen atoms, resulting in a decrease in mass.
Correct Answer: Loss of electrons, resulting in an increase in oxidation number.
Rationale: Oxidation is defined as the loss of electrons by a species, which corresponds to an increase
in its oxidation number. Option A describes reduction, option C confuses electron transfer with proton
transfer, and option D describes a chemical change that is not the defining feature of oxidation.
2. What is the oxidation number of sulfur in the sulfate ion, SO4^2-?
A) +2
B) +4
C) +6
D) -2
,Correct Answer: +6
Rationale: In SO4^2-, oxygen is assigned an oxidation number of -2. The sum of oxidation numbers
must equal the ion's charge of -2. Letting x be the oxidation number of sulfur: x + 4(-2) = -2, so x = +6.
Options A, B, and D result from incorrect algebraic setups or ignoring the overall charge.
3. In the reaction Zn(s) + Cu^2+(aq) → Zn^2+(aq) + Cu(s), which species is the reducing agent?
A) Zn(s)
B) Cu^2+(aq)
C) Zn^2+(aq)
D) Cu(s)
Correct Answer: Zn(s)
Rationale: The reducing agent is the species that donates electrons and is itself oxidized. Zn(s) loses
electrons to become Zn^2+, so it is oxidized and acts as the reducing agent. Cu^2+ is reduced and acts
as the oxidizing agent. Options C and D are products and do not function as agents in the forward
reaction.
4. Which of the following is the correct half-reaction for the reduction of MnO4- to Mn^2+ in acidic
solution?
A) MnO4- + 8 H+ + 5 e- → Mn^2+ + 4 H2O
B) MnO4- + 4 H+ + 3 e- → Mn^2+ + 2 H2O
C) MnO4- + 8 H+ + 3 e- → Mn^2+ + 4 H2O
, D) MnO4- + 4 H2O + 5 e- → Mn^2+ + 8 OH-
Correct Answer: MnO4- + 8 H+ + 5 e- → Mn^2+ + 4 H2O
Rationale: Balancing the reduction of MnO4- to Mn^2+ in acid requires adding 8 H+ to the reactant
side to balance oxygen atoms as water and 5 electrons to balance the charge. Option B has an
incorrect electron count, option C has incorrect electron and hydrogen counts, and option D is the
half-reaction for basic solution.
5. A galvanic cell is constructed with a standard hydrogen electrode (SHE) as the anode and a
Cu^2+/Cu electrode as the cathode. If E° for Cu^2+/Cu is +0.34 V, what is the standard cell potential?
A) -0.34 V
B) 0.00 V
C) +0.34 V
D) +0.68 V
Correct Answer: +0.34 V
Rationale: E°cell = E°cathode - E°anode. The SHE has E° = 0.00 V by definition, and the copper
electrode has E° = +0.34 V. Thus, E°cell = 0.34 - 0.00 = +0.34 V. Options A and B are incorrect signs or
values, and option D incorrectly doubles the potential.
6. Which of the following statements about a voltaic cell is correct?
A) Oxidation occurs at the cathode, and reduction occurs at the anode.
w/Lab | Portage | 26/27|Q&A Actual (PDF)
1. Which statement correctly defines oxidation in the context of electron transfer?
A) Gain of electrons, resulting in a decrease in oxidation number.
B) Loss of electrons, resulting in an increase in oxidation number.
C) Gain of protons, resulting in a decrease in pH.
D) Loss of oxygen atoms, resulting in a decrease in mass.
Correct Answer: Loss of electrons, resulting in an increase in oxidation number.
Rationale: Oxidation is defined as the loss of electrons by a species, which corresponds to an increase
in its oxidation number. Option A describes reduction, option C confuses electron transfer with proton
transfer, and option D describes a chemical change that is not the defining feature of oxidation.
2. What is the oxidation number of sulfur in the sulfate ion, SO4^2-?
A) +2
B) +4
C) +6
D) -2
,Correct Answer: +6
Rationale: In SO4^2-, oxygen is assigned an oxidation number of -2. The sum of oxidation numbers
must equal the ion's charge of -2. Letting x be the oxidation number of sulfur: x + 4(-2) = -2, so x = +6.
Options A, B, and D result from incorrect algebraic setups or ignoring the overall charge.
3. In the reaction Zn(s) + Cu^2+(aq) → Zn^2+(aq) + Cu(s), which species is the reducing agent?
A) Zn(s)
B) Cu^2+(aq)
C) Zn^2+(aq)
D) Cu(s)
Correct Answer: Zn(s)
Rationale: The reducing agent is the species that donates electrons and is itself oxidized. Zn(s) loses
electrons to become Zn^2+, so it is oxidized and acts as the reducing agent. Cu^2+ is reduced and acts
as the oxidizing agent. Options C and D are products and do not function as agents in the forward
reaction.
4. Which of the following is the correct half-reaction for the reduction of MnO4- to Mn^2+ in acidic
solution?
A) MnO4- + 8 H+ + 5 e- → Mn^2+ + 4 H2O
B) MnO4- + 4 H+ + 3 e- → Mn^2+ + 2 H2O
C) MnO4- + 8 H+ + 3 e- → Mn^2+ + 4 H2O
, D) MnO4- + 4 H2O + 5 e- → Mn^2+ + 8 OH-
Correct Answer: MnO4- + 8 H+ + 5 e- → Mn^2+ + 4 H2O
Rationale: Balancing the reduction of MnO4- to Mn^2+ in acid requires adding 8 H+ to the reactant
side to balance oxygen atoms as water and 5 electrons to balance the charge. Option B has an
incorrect electron count, option C has incorrect electron and hydrogen counts, and option D is the
half-reaction for basic solution.
5. A galvanic cell is constructed with a standard hydrogen electrode (SHE) as the anode and a
Cu^2+/Cu electrode as the cathode. If E° for Cu^2+/Cu is +0.34 V, what is the standard cell potential?
A) -0.34 V
B) 0.00 V
C) +0.34 V
D) +0.68 V
Correct Answer: +0.34 V
Rationale: E°cell = E°cathode - E°anode. The SHE has E° = 0.00 V by definition, and the copper
electrode has E° = +0.34 V. Thus, E°cell = 0.34 - 0.00 = +0.34 V. Options A and B are incorrect signs or
values, and option D incorrectly doubles the potential.
6. Which of the following statements about a voltaic cell is correct?
A) Oxidation occurs at the cathode, and reduction occurs at the anode.
