Redox Review
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. After balancing the redox equation BrO2 + OH– + N2O4  BrO3– + H2O + NO2–, the coefficients, in order
from left to right, are
a. 1, 4, 3, 1, 4, 6.
c. 2, 6, 2, 2, 4, 12.
b. 2, 4, 1, 2, 2, 2.
d. 1, 8, 3, 2, 4, 2.
____
2. After balancing the redox equation HBr + NaMnO4  NaBr + MnBr2 + Br2 + H2O, the coefficients, in order
from left to right, are
a. 8, 2, 2, 2, 5, 8.
c. 16, 2, 2, 2, 3, 4.
b. 4, 1, 1, 1, 3, 2.
d. 16, 2, 2, 2, 5, 8.
____
3. After balancing the redox equation FeCl2 + KMnO4 + HCl  FeCl3 + MnCl2 + H2O + KCl, the coefficients,
in order from left to right, are
a. 3, 1, 4, 3, 1, 2, 1.
c. 5, 1, 8, 5, 1, 4, 1.
b. 4, 2, 5, 4, 2, 3, 2.
d. 5, 1, 4, 5, 1, 4, 1.
____
4. After balancing the redox equation Cr2O72– + SO2 + H+  Cr3+ + HSO4– + H2O, the coefficients, in order from
left to right, are
a. 1, 3, 5, 2, 3, 1.
c. 2, 5, 10, 4, 5, 2.
b. 1, 2, 4, 2, 2, 1.
d. 2, 1, 2, 5, 1, 2.
____
5. After balancing the redox equation FeSO4 + KMnO4 + H2SO4  Fe2(SO4)3 + MnSO4 + K2SO4 + H2O, the
coefficients, in order from left to right, are
a. 5, 4, 8, 5, 1, 2, 4.
c. 10, 2, 8, 5, 2, 1, 8.
b. 2, 5, 3, 2, 5, 1, 4.
d. 5, 1, 4, 3, 1, 1, 4.
____
6. After balancing the redox equation in which elemental chlorine reacts with sodium hydroxide to produce
sodium hypochlorite (NaClO), water, and sodium chloride, the coefficients of these substances are,
respectively,
a. 1, 1, 1, 1, 1.
c. 2, 4, 2, 1, 2.
b. 1, 2, 1, 1, 1.
d. 1, 2, 1, 2, 1.
____
7. After balancing the redox equation FeCl3 + Zn  ZnCl2 + Fe, the coefficients, in order from left to right, are
a. 2, 2, 1, 2.
c. 4, 3, 3, 4.
b. 1, 1, 1, 1.
d. 2, 3, 3, 2.
____
8. After balancing the redox equation Bi(OH)3 + SnO22–  Bi + SnO32– + H2O, the coefficients, in order from
left to right, are
a. 4, 5, 4, 6, 6.
c. 3, 5, 3, 5, 5.
b. 2, 3, 2, 3, 3.
d. 2, 1, 2, 1, 3.
Relative Strength of Oxidizing and
Reducing Agents
Reducing Agents
Oxidizing Agents
S
Li
Li+
W
T
K
K+
E
R
Ca
Ca2+
A
O
N
G
E
R
W
E
A
K
E
R
____
Na
Mg
Al
Zn
Cr
Fe
Ni
Sn
Pb
H2
H2S
Cu
I–
MnO42–
Fe2+
Hg
Ag
NO2–
Br–
Mn2+
SO2
Cr3+
Cl–
Mn2+
F–
Na+
Mg2+
Al3+
Zn2+
Cr3+
Fe2+
Ni2+
Sn2+
Pb2+
H3O+
S
Cu2+
I2
MnO4–
Fe3+
Hg22+
Ag+
NO3–
Br2
MnO2
H2SO4 (conc.)
Cr2O72–
Cl2
MnO4–
F2
K
E
R
S
T
R
O
N
G
E
R
9. In the figure above, which ion oxidizes Sn to Sn2+ but does NOT oxidize Hg to Hg22+?
a. NO3–
c. Cr2O72–
3+
b. Al
d. Cu2+
____ 10. In the figure above, which ion is reduced by Zn but reduces Ag+ to Ag?
a. Mg2+
c. Fe2+
3+
b. Fe
d. NO3–
____ 11. In the figure above, which element displaces Cu2+ ions from solution but is displaced by Ni metal when it is in
ionic form?
a. Al
c. Fe
b. Ag
d. Pb
____ 12. What is the oxidation number of a free element?
a. its group number
c. +1
b. its total number of valence electrons
d. 0
____ 13. What are the oxidation numbers in the compound KCl?
a. K = 0, Cl = 0
c. K = +1, Cl = –1
b. K = –1, Cl = +1
d. K = +2, Cl = –2
____ 14. What are the oxidation numbers in the compound H2O2?
a. H = +1, O = –2
c. H = +2, O = –2
b. H = –1, O = –2
d. H = +1, O = –1
____ 15. What are the oxidation numbers in the compound NO2?
a. N = +2, O = –1
c. N = –2, O = +1
b. N = +2, O = –2
d. N = +4, O = –2
____ 16. What are the oxidation numbers in the compound H3PO4?
a. H = +1, P = 0, O = –2
c. H = –1, P = +7, O = –1
b. H = +1, P = +5, O = –2
d. H = +1, P = +1, O = –1
____ 17. What are the oxidation numbers in the ion SO32–?
a. S = +6, O = –2
c. S = +4, O = –2
b. S = +1, O = –1
d. S = 0, O = –1
____ 18. In the reaction O2 + 4e–  2O2–, the species O2 is
a. oxidized.
c. electrolyzed.
b. reduced.
d. autooxidized.
____ 19. In the reaction Fe  Fe3+ + 3e–, the species Fe is
a. oxidized.
c. electrolyzed.
b. reduced.
d. autooxidized.
____ 20. In the reaction 2K + Br2  2K+ + 2Br–, which species is reduced?
a. K only
c. both K and Br2
b. Br2 only
d. neither K nor Br2
____ 21. In the reaction F2 + Mg  2F– + Mg2+, which species is oxidized?
a. F2 only
c. both Mg and F2
b. Mg only
d. neither Mg nor F2
____ 22. In the reaction Na+ + Br–  NaBr, which species is reduced?
a. Na+ only
c. both Na+ and Br–
–
b. Br only
d. neither Na+ nor Br–
____ 23. Which of the following is an oxidation-reduction reaction?
a. H2  2H
b. 2O–  O22–
c. H2 + Cl2  2HCl
d. HCl + NaBr  HBr + NaCl
____ 24. Which of the following is an oxidation-reduction reaction?
a. Na  Na+ + e–
c. N2O4  2NO2
b. 2SO2 + O2  2SO3
d. 2e– + F2  2F–
____ 25. Which of the following is NOT an oxidation-reduction reaction?
a. H2O + SO2  H2SO3
b. N2 + O2  2NO
c. H2 + Cl2  2HCl
d. 2NaBr + Cl2  2NaCl + Br2
____ 26. Which of the following substances could be produced from SO3 only by an oxidation-reduction reaction?
a. H2SO4
c. SF6
b. H2SO3
d. None of the above
____ 27. In a redox reaction, MnO4– is changed to Mn2+. How many electrons must be lost or gained by Mn?
a. two lost
b. two gained
c. five lost
d. five gained
____ 28. In a redox reaction, MnO4– is changed to MnO42–. How many electrons must be lost or gained by Mn?
a. none lost or gained
c. one gained
b. one lost
d. two gained
____ 29. In a redox reaction, CO is changed to CO2. How many electrons must be lost or gained by C?
a. one lost
c. two lost
b. one gained
d. two gained
____ 30. The redox equation 4H+ + N2  NH4+ + N is
a. correctly balanced.
b. correctly balanced for number of atoms but not for charge.
c. correctly balanced for charge but not for number of atoms.
d. not balanced for number of atoms or charge.
____ 31. The redox equation MnO4– + 4CO2 + 4H+  4CO3+ + Mn2+ + 4H2O is
a. correctly balanced.
b. correctly balanced for number of atoms but not for charge.
c. correctly balanced for charge but not for number of atoms.
d. not balanced for number of atoms or charge.
____ 32. The redox equation Cu2+ + 2Fe  Cu + 2Fe2+ is
a. correctly balanced.
b. correctly balanced for number of atoms but not for charge.
c. correctly balanced for charge but not for number of atoms.
d. not balanced for number of atoms or charge.
____ 33. The redox equation H2 + O2  2H+ + O2– is
a. correctly balanced.
b. correctly balanced for number of atoms but not for charge.
c. correctly balanced for charge but not for number of atoms.
d. not balanced for number of atoms or charge.
____ 34. The redox equation H2 + S + 2O2  2H+ + SO42– is
a. correctly balanced.
b. correctly balanced for number of atoms but not for charge.
c. correctly balanced for charge but not for number of atoms.
d. not balanced for charge or number of atoms.
____ 35. Which is the most active reducing agent among the elements?
a. cesium
c. fluorine
b. iodine
d. lithium
____ 36. Which is the most active oxidizing agent among the elements?
a. cesium
c. fluorine
b. iodine
d. lithium
____ 37. Which of the following reactions is an autooxidation?
a. 2H2O2  2H2O + O2
b. 2H2O  H3O+ + OH–
c. Cu + 2AgNO3  Cu(NO3)2 + 2Ag
d. 2Li + 2H2O  2LiOH + H2
____ 38. When hydrogen peroxide decomposes, usually the only products are
a. hydrogen and oxygen.
c. oxygen and water.
b. hydrogen and water.
d. hydrogen, oxygen, and water.
____ 39. Which of the following reactions is an autooxidation?
a. 2NO2  N2O4
c. 2NO + O2  2NO2
b. N2O3  NO2 + NO
d. N2 + O2  2NO
____ 40. Give the oxidation numbers for the oxygen atoms in H2O2, H2O, and O2, respectively.
a. –2, –1, 0
c. –2, –2, 0
b. –1, –2, 0
d. –1, 0, 0
____ 41. What is the oxidation number of a monatomic ion?
a. 0
c. its charge
b. +1
d. its number of electrons
____ 42. What is the most common oxidation number of combined oxygen?
a. –2
c. 0
b. –1
d. +1
____ 43. What is the most common oxidation number of combined hydrogen?
a. –2
c. 0
b. –1
d. +1
____ 44. The algebraic sum of the oxidation numbers of the atoms in a compound
a. is always zero.
c. is always –1.
b. is always +1.
d. can be any whole number.
____ 45. In an oxidation, atoms or ions
a. increase their oxidation number.
b. decrease their oxidation number.
c. do not change their oxidation number.
d. have a zero oxidation number after the reaction.
____ 46. In a reduction, atoms or ions
a. increase their oxidation number.
b. decrease their oxidation number.
c. do not change their oxidation number.
d. have a zero oxidation number after the reaction.
____ 47. Which of the following are numbers assigned to atoms and ions to keep track of electrons?
a. charges
c. electrode potentials
b. coefficients
d. oxidation numbers
____ 48. A species whose oxidation number decreases in a reaction is
a. oxidized.
c. electrolyzed.
b. reduced.
d. autooxidized.
____ 49. A species whose oxidation number increases in a reaction is
a. oxidized.
c. electrolyzed.
b. reduced.
d. autooxidized.
____ 50. Oxidation and reduction
a. always occur simultaneously.
b. always occur at different times.
c. do not occur in the same reaction.
d. always occur with oxidation first, then reduction.
____ 51. If species change their oxidation numbers, the process is a(n)
a. synthesis.
c. electrolysis.
b. decomposition.
d. oxidation-reduction reaction.
____ 52. Another name for an oxidation-reduction reaction is a(n)
a. double-replacement reaction.
c. electrochemical reaction.
b. redox reaction.
d. decomposition reaction.
____ 53. In a balanced redox equation, how does the total number of reactant molecules compare with the total number
of product molecules?
a. The two numbers are always equal.
b. Reactant molecules are always more numerous.
c. Product molecules are always more numerous.
d. No relationship exists between the two numbers.
____ 54. In a balanced redox equation, how does the total number of reactant atoms compare with the total number of
product atoms?
a. The two numbers are always equal.
b. Reactant atoms are always more numerous.
c. Product atoms are always more numerous.
d. No relationship exists between the two numbers.
____ 55. In a balanced redox equation, how does the total charge of reactants compare with the total charge of
products?
a. The two totals are always equal.
b. Total reactant charge is always greater.
c. Total product charge is always greater.
d. No relationship exists between the two totals.
____ 56. During redox reactions, oxidizing agents
a. increase their oxidation number.
b. decrease their oxidation number.
c. keep the same oxidation number.
d. do not participate.
____ 57. During redox reactions, reducing agents
a. increase their oxidation number.
b. decrease their oxidation number.
c. keep the same oxidation number.
d. do not participate.
____ 58. In redox reactions,
a. the oxidizing agent is the substance oxidized.
b. the reducing agent is the substance oxidized.
c. both oxidizing and reducing agents are oxidized.
d. the reducing agent is the substance reduced.
____ 59. What is the formula of the peroxide ion?
a. O2–
b. O–
c. O2–
d. O22–
____ 60. When hydrogen peroxide decomposes, oxygen is
a. reduced only.
c. both oxidized and reduced.
b. oxidized only.
d. electrolyzed.
85.
In which of the following does nitrogen have an oxidation state of +4?
a)
HNO3
b)
NO2
c)
N2O
d)
NH4Cl
e)
NaNO2
86.
The oxidation state of iodine in IO3– is:
a)
0
b)
+3
c)
–3
d)
+5
e)
–5
87.
The oxidation state of chlorine in ClO3– is:
a)
0
b)
+5
c)
-5
d)
+7
e)
-7
88.
Which of the following statements is not true?
a)
When a metal reacts with a nonmetal, an ionic compound is formed.
b)
A metal-nonmetal reaction can always be assumed to be an oxidation-reduction reaction.
c)
Two nonmetals can undergo an oxidation-reduction reaction.
d)
When two nonmetals react, the compound formed is ionic.
e)
A metal-nonmetal reaction involves electron transfer.
89.
In the reaction 2Ca(s) + O2(g)  2CaO(s), which species is oxidized?
a)
O2
b)
O2–
c)
Ca
d)
Ca2+
e)
none of these
90.
In the reaction 2Cs(s) + Cl2(g)  2CsCl(s), Cl2 is
a)
the reducing agent
b)
the oxidizing agent
c)
oxidized
d)
the electron donor
e)
two of these
91.
In the reaction N2(g) + 3H2(g)  2NH3(g), N2 is
a)
oxidized
b)
reduced
c)
the electron donor
d)
the reducing agent
e)
two of these
92.
In the reaction P4(s) + 10Cl2(g)  4PCl5(s), the reducing agent is
a)
chlorine
b)
PCl5
c)
phosphorus
d)
Cl–
e)
none of these
93.
In the reaction C(s) + O2(g)  CO2(g) carbon is __________.
a)
the reducing agent
b)
the electron acceptor
c)
d)
e)
reduced
the oxidizing agent
more than one of these
94.
Which of the following reactions does not involve oxidation-reduction?
a)
CH4 + 3O2  2H2O + CO2
b)
Zn + 2HCl  ZnCl2 + H2
c)
2Na + 2H2O  2NaOH + H2
d)
MnO2 + 4HCl  Cl2 + 2H2O + MnCl2
e)
All are oxidation-reduction reactions.
95.
Which of the following are oxidation-reduction reactions?
I.
PCl3 + Cl2  PCl5
II.
Cu + 2AgNO3  Cu(NO3)2 + 2Ag
III.
CO2 + 2LiOH  Li2CO3 + H2O
IV.
FeCl2 + 2NaOH  Fe(OH)2 + 2NaCl
a)
b)
c)
d)
e)
III
IV
I and II
I, II, and III
I, II, III, and IV
96.
Which of the following statements is(are) true? Oxidation and reduction
a)
cannot occur independently of each other
b)
accompany all chemical changes
c)
describe the loss and gain of electron(s), respectively
d)
result in a change in the oxidation states of the species involved
e)
A, C, and D
97.
In the reaction Zn + H2SO4  ZnSO4 + H2, which, if any, element is oxidized?
a)
zinc
b)
hydrogen
c)
sulfur
d)
oxygen
e)
none of these
98.
In the following reaction, which species is oxidized?
8NaI + 5H2SO4  4I2 + H2S + 4Na2SO4 + 4H2O
a)
b)
c)
d)
e)
99.
sodium
iodine
sulfur
hydrogen
oxygen
How many of the following are oxidation-reduction reactions?
NaOH + HCl  NaCl + H2O
Cu + 2AgNO3 2Ag + Cu(NO3)2
Mg(OH)2  MgO + H2O
N2 + 3H2  2NH3
a)
b)
c)
d)
e)
0
1
2
3
4
100. In the reaction shown below, what species is oxidized?
2NaI + Br2  2NaBr + I2
Na+
I–
Br2
Br–
I2
a)
b)
c)
d)
e)
101. T
F
Oxidation is the gain of electrons.
102. T
F
A reducing agent is an electron donor.
103. Balance the following oxidation-reduction reaction using the oxidation number method:
Fe3+ + I–  Fe2+ + I2
In the balanced equation, the coefficient of Fe2+ is
a)
b)
c)
d)
e)
1
2
3
4
none of these
104. Balance the following oxidation-reduction reaction using the oxidation number method:
Al + Br2  Al3+ + Br–
In the balanced equation, the coefficient of Br– is
a)
b)
c)
d)
e)
2
3
4
6
none of these
105. Consider the following unbalanced oxidation-reduction reaction:
Fe + Br2  Fe3+ + Br–
In the balanced equation, the number of electrons transferred is
a)
b)
c)
d)
e)
3
2
6
4
none of these
106. The MnO4– is often used to analyze for the Fe2+ content of an aqueous solution via the reaction
MnO4–(aq) + Fe2+(aq) + H+(aq) Fe3+(aq) + Mn2+(aq) + H2O(l)
What is the ratio of Fe2+ : MnO4– in the balanced equation?
a)
b)
c)
d)
e)
1:1
2:1
3:1
4:1
5:1
107. Given the reaction:
2MnO4– + 5H2O2 + 6H+  2Mn2+ + 8H2O + 5O2
determine the number of electrons involved in this reaction.
a)
b)
c)
d)
e)
10
8
6
4
2