Deck 14: Oxidation and Reduction

Question 1

Given:
Li + Hg₂I₂ → 2LiI + 2Hg
The equation is a balanced reaction.
Refer to the reaction below for True/False Questions 13-14.
Given:
Fe + MnO₄⁻ $\rightarrow$ Fe³⁺ + Mn

Answer 1

False

Question 2

When an oxidation number of an atom is increased in the course of a redox reaction, that atom is being reduced.

Answer 2

False

Question 3

Given:
Mo²⁺ + Br₂ → Mo³⁺ + 2Br⁻
The equation is a balanced reaction.

Answer 3

False

Question 4

The phosphorous atom in H₃PO₄ is assigned an oxidation number of +5.

Question 5

The fluorine atom in HF is assigned an oxidation number of +1.

Question 6

If the reaction is taking place in an acidic solution, 6 moles of H₂O are required on the product side to balance the equation.

Question 7

The sodium atom in NaOH is assigned an oxidation number of +1.

Question 8

If the reaction is taking place in a basic solution the balanced equation of the reaction is
7Fe + 3MnO₄⁻ $\rightarrow$ 7Fe³⁺ + 3Mn + 24OH⁻ + 12H₂O.

Question 9

When an oxidation number of an atom is decreased in the course of a redox reaction, that atom is being oxidized.

Question 10

The calcium atom in Ca₃(PO₄)₂ is assigned an oxidation number of +3.

Question 11

Given:
O₂ + 2H₂O + I₂ → 4OH⁻ + 2I⁻
The equation is a balanced reaction.

Question 12

The oxygen atom in O₂ is assigned an oxidation number of -1.

Question 13

Given:
Ru₂S₃ + O₂ → Ru₂O₃ + S
The coefficient of Ru₂S₃ is 2 in the balanced chemical equation.

Question 14

The value of E_1/2 for the half reaction O₂ + 4H⁺ + 4e⁻ → 2H₂O is 1.23 V.

Question 15

Given:
Na + I₂ → NaI
The coefficient of Na is 2 in the balanced chemical equation.

Question 16

Atoms in their elemental state are assigned an oxidation number of 0.

Question 17

Given:
Be + 2H⁺ → Be²⁺ + H₂
The equation is a balanced reaction.

Question 18

The voltage of a voltaic cell based on the reaction O₂ + 4H⁺ + 4Cl⁻→ 2H₂O + 2Cl₂ is 0.15 V.

Question 19

The value of E_1/2 for the half reaction Mn²⁺ + 4H₂O → MnO₄⁻ + 8H⁺ + 5e⁻ is 1.51 V.

Question 20

The reaction taking place in the voltaic cell Ag⁺ + Fe²⁺ → Ag + Fe³⁺ is a nonspontaneous reaction.

Question 21

The oxidation number of the hydrogen atom in InH₃ is _____.

A) +2
B) -2
C) -1
D) 0
E) -3
Refer to the reaction below for 33-34.
Given:
2RbOH + H₂SO₄ $\rightarrow$ Rb₂SO₄ + 2H₂O

Question 22

The reaction taking place in the voltaic cell Pb²⁺ + H₂ → Pb + 2H⁺ is a spontaneous reaction.

Question 23

The half reaction for the electrolysis of elemental bromine is 2Br⁻ → Br₂ + 2e⁻.

Question 24

The oxidation number for the calcium atom in Ca₃(PO₄)₂ is _____.

A) +4
B) +3
C) -3
D) +2
E) +6

Question 25

What happens to the H atom?

A) Oxidation number increases from -1 to +1
B) Oxidation number decreases from +1 to 0
C) Oxidation number remains the same at +1
D) Oxidation number decreases from -1 to 0
E) Oxidation number remains the same at +2
Refer to the reaction below for 41-43.
Given:
Mg + O₂ $\rightarrow$ MgO

Question 26

What happens to the oxidation number of the S atom?

A) The oxidation number remains the same at +2.
B) The oxidation number changes from 0 to +2.
C) The oxidation number remains the same at +6.
D) The oxidation number changes from -2 to +2.
E) The oxidation number remains the same at +4.

Question 27

Given: NH₃ + HCl $\rightarrow$ NH₄Cl
Which of the following is taking place in the reaction?

A) The oxidation number of the hydrogen atom increases from +3 to +4; so it is being oxidized.
B) The oxidation number of the chlorine atom decreases from 0 to +1; so it is being oxidized.
C) The oxidation number of the chlorine atom decreases from +1 to 0; so it is being reduced.
D) The oxidation number of the nitrogen atom increases from -3 to +4, so it is being oxidized.
E) The oxidation number of the nitrogen atom remains the same at -3.

Question 28

What happens to the oxidation number of the Rb atom?

A) The oxidation number remains the same at -2.
B) The oxidation number changes from 0 to +1.
C) The oxidation number remains the same at +1.
D) The oxidation number changes from -2 to +1.
E) The oxidation number changes from -1 to +2.

Question 29

Given: Fe + I₂ → FeI₂
Identify what is being oxidized and reduced in this redox reaction.

A) Oxidation numbers of all the atoms remain the same.
B) Fe is being reduced from 0 to -2; I is being oxidized from -1 to 0.
C) Fe is being oxidized from 0 to +1; I is being reduced from +2 to 0.
D) Fe is being reduced from 0 to -1; I is being oxidized from 0 to +2.
E) Fe is being oxidized from 0 to +2; I is being reduced from 0 to -1.

Question 30

If the voltage of the voltaic cell based on the reaction Cu²⁺ + 2I⁻ → I₂ + Cu is 0.88 V, the standard reduction potential of the Cu²⁺ + 2e⁻ → Cu half-cell is 0.54 V.

Question 31

The half reaction for the electrolysis of elemental chlorine is Cl²⁺ + 2e⁻ → Cl₂.

Question 32

Atoms in their elemental state are assigned an oxidation number of _____.

A) 1
B) 2
C) -2
D) 3
E) 0

Question 33

Given: 6H⁺+ 2MnO₄⁻ + 5H₂O₂ → 2Mn⁺² + 5O₂ + 8H₂O
Identify what is being oxidized and reduced in this redox reaction.

A) Oxidation numbers of all the atoms remain the same.
B) H is being oxidized from +6 to +8; Mn stays the same.
C) O is being oxidized from -1 to 0; Mn is being reduced from +7 to +2.
D) Mn is being oxidized from -4 to -2; O is being reduced from +6 to +5.
E) H is being oxidized from +6 to +5; Mn is being reduced from +1 to -2.

Question 34

The oxidation number for the fluorine atom in CaF₂ is ____.

A) 0
B) -3
C) -1
D) +2
E) -2

Question 35

If the voltage of the voltaic cell 6I⁻ + 2NO₃⁻ + 8H⁺ + 6e⁻ → 2NO + 4H₂O + 3I₂ is 1.50 V, the standard reduction potential of the NO₃⁻ + 4H⁺ + 3e⁻ → NO + 2H₂O half-cell reaction is -0.96 V.

Question 36

The oxidation number for the chlorine atom in Cl₂ is _____.

A) 0
B) +3
C) +1
D) +2
E) -2

Question 37

Redox reactions require _____ to keep track of electrons assigned to each atom in a chemical reaction.

A) mass numbers
B) oxidation numbers
C) number of neutrons
D) magnetic quantum numbers
E) spin quantum numbers

Question 38

The oxidation number for the oxygen atom in BaO₂ is ____.

A) -3
B) -1
C) -2
D) +2
E) 0

Question 39

Given: HCN + NaOH $\rightarrow$ NaCN + H₂O
Which of the following is taking place in the reaction?

A) The oxidation numbers of all the atoms remain the same.
B) The oxidation number of the nitrogen atom increases from +3 to +4.
C) The oxidation number of the nitrogen atom decreases from +4 to +3.
D) The oxidation number of the hydrogen atom decreases from +2 to +1.
E) The oxidation number of the carbon atom increases from +2 to +3.
Refer to the reaction below for 39-40.
Given:
2CH₄ + 3O₂ $\rightarrow$ 2CO + 4H₂O

Question 40

C is being _____.

A) oxidized from +3 to +4
B) oxidized from -4 to +2
C) reduced from +4 to -2
D) reduced from -1 to -2
E) reduced from -1 to -3

Question 41

The coefficient of O₂ after balancing the equation is _____.

A) 1
B) 2
C) 5
D) 3
E) 4

Question 42

The coefficient of Sr after balancing the equation is _____.

A) 1
B) 5
C) 3
D) 2
E) 4

Question 43

The coefficient of F₂ after balancing the equation is _____.

A) 1
B) 5
C) 3
D) 2
E) 4

Question 44

The coefficient of PI₃ after balancing the equation is _____.

A) 3
B) 5
C) 6
D) 2
E) 4

Question 45

The coefficient of Mg after balancing the equation is _____.

A) 1
B) 2
C) 5
D) 3
E) 4

Question 46

If the reaction is taking place in an acidic solution, what is the number of moles of water required on the product or reactant side to balance the redox reaction?

A) 14 moles of H₂O on the reactant side
B) 14 mole2 of H₂O on the product side
C) No moles of H₂O
D) 7 moles of H₂O on the reactant side
E) 7 moles of H₂O on the product side

Question 47

The coefficient of H⁺ after balancing the equation is _____.

A) 1
B) 5
C) 3
D) 2
E) 4

Question 48

The coefficient of P₂O₅ after balancing the equation is _____.

A) 3
B) 5
C) 6
D) 2
E) 4

Question 49

The coefficient of MgO after balancing the equation is _____.

A) 1
B) 2
C) 5
D) 3
E) 4
Refer to the reaction below for 44-47.
Given:
P₂O₅ + I₂ → PI₃ + O₂

Question 50

The coefficient of O₂ after balancing the equation is _____.

A) 3
B) 5
C) 6
D) 2
E) 4
Refer to the reaction below for 48-51.
Given:
Sr + H⁺→ Sr²⁺ + H₂

Question 51

If the reaction is taking place in a basic solution, what is the number of moles of water required on the product or reactant side to balance the redox reaction?

A) 7 moles of H₂O on the reactant side
B) 7 moles of H₂O on the product side
C) 14 moles of H₂O on the reactant side
D) No moles of H₂O
E) 14 moles of H₂O on the product side

Question 52

The coefficient of Cl₂ after balancing the equation is _____.

A) 2
B) 5
C) 3
D) 1
E) 4

Question 53

The coefficient of Sr²⁺ after balancing the equation is _____.

A) 1
B) 5
C) 3
D) 2
E) 4

Question 54

The coefficient of Au after balancing the equation is _____.

A) 1
B) 5
C) 3
D) 2
E) 4

Question 55

The coefficient of Au⁺ after balancing the equation is _____.

A) 1
B) 5
C) 3
D) 2
E) 4

Question 56

The coefficient of H₂ after balancing the equation is _____.

A) 1
B) 5
C) 3
D) 2
E) 4
Refer to the reaction below for 52-54.
Given:
Au⁺ → Au + Au³⁺ (Hint: both half reactions will start with the same reactant.)

Question 57

The coefficient of Cl⁻ after balancing the equation is _____.

A) 1
B) 5
C) 3
D) 2
E) 4

Question 58

The coefficient of Au³⁺ after balancing the equation is _____.

A) 1
B) 5
C) 3
D) 2
E) 4
Refer to the reaction below for 55-58.
Given:
Cl⁻ + F₂ → F⁻ + Cl₂

Question 59

The coefficient of F⁻ after balancing the equation is _____.

A) 1
B) 2
C) 5
D) 3
E) 4
Refer to the reaction below for 59-62.
Given:
Cr₂O₇²⁻ + Fe → Cr³⁺ + Fe³⁺

Question 60

The coefficient of I₂ after balancing the equation is _____.

A) 3
B) 5
C) 6
D) 2
E) 4

Question 61

What is the half reaction for the electrolysis of elemental nickel?

A) Ni²⁺ + 2e⁻ → Ni
B) Ni⁺ + e⁻ → Ni
C) Ni³⁺+ 3e⁻ →Ni
D) Ni₂ + 2e⁻ → 2Ni⁻
E) 2Ni⁺ + 2e⁻ → Ni₂

Question 62

What is the E of a voltaic cell based on this reaction? F₂ + Pb → 2F^- + Pb²⁺

A) 2.74 V
B) 22.7 V
C) 2.99 V
D) 0.362 V
E) 5.49 V

Question 63

Atoms in monatomic (i.e., one-atom) ions are assigned an oxidation number equal to their charge. Oxidation numbers are usually written with the sign first, then the magnitude, to differentiate them from charges.

Question 64

Briefly describe the method of balancing a redox reaction by the half reaction method.

Question 65

What is the E of a voltaic cell based on this reaction? MnO₄⁻ + 6H⁺ + H₂ → Mn²⁺ + 4H₂O

A) -1.10 V
B) +1.10 V
C) +1.51 V
D) +3.68 V
E) +1.23 V

Question 66

Briefly describe the rules required for assigning oxidation numbers.

Question 67

What is the half reaction for the electrolysis of elemental iodine?

A) I₂ → 2I⁻ + 2e⁻
B) I²⁺ + 2e⁻ → I
C) 2I⁻ → I₂ + 2e⁻
D) 2I⁺ + 2e⁻ → I₂
E) I₂ + 2e⁻ → 2I⁻

Question 68

Briefly enumerate the steps involved in balancing a redox reaction with an example. Assume a basic solution.

Question 69

Briefly describe the method of balancing a redox reaction by inspection.

Question 70

What is the E of a voltaic cell based on this reaction? 2Mn²⁺ + 8H₂O + 5Sn⁴⁺ → 2MnO₄^- + 16H⁺ + 5Sn²⁺

A) -10.1 V
B) -1.36 V
C) +10.1 V
D) +0.227 V
E) +1.81 V

Question 71

If the reaction is taking place in a basic solution, the balanced equation is:

A) 14H₂O + 2Cr₂O₇²⁻ + 2Fe $\rightarrow$ 2Cr³⁺ + 14OH⁻ + 4Fe³⁺.
B) 14H₂O + Cr₂O₇²⁻ + 5Fe $\rightarrow$ 2Cr³⁺ + 14OH⁻ + 5Fe³⁺.
C) 7H₂O + Cr₂O₇²⁻ + 2Fe $\rightarrow$ 2Cr³⁺ + 14OH⁻ + 2Fe³⁺.
D) H₂O + Cr₂O₇²⁻ + Fe $\rightarrow$ Cr³⁺ + OH⁻ + Fe³⁺.
E) 7H₂O + 7Cr₂O₇²⁻ + 7Fe $\rightarrow$ 7Cr³⁺ + 14OH⁻ + 7Fe³⁺.
Refer to the Table 14.1 for 63-67.

Question 72

If the reaction is taking place in an acidic solution, the balanced equation is:

A) 2Fe + 14H⁺ + 2Cr₂O₇²⁻ → 2Fe³⁺ + 2Cr³⁺ + 2H₂O.
B) Fe + H⁺ + Cr₂O₇²⁻ → Fe³⁺ + Cr³⁺ + H₂O.
C) 2Fe + 14H⁺ + Cr₂O₇²⁻ → 4Fe³⁺ + 2Cr³⁺ + 28H₂O.
D) 2Fe + 14H⁺ + Cr₂O₇²⁻ → 2Fe³⁺ + 2Cr³⁺ + 7H₂O.
E) 4Fe + 10H⁺ + Cr₂O₇²⁻ → 3Fe³⁺ + Cr³⁺ + 7H₂O.

Question 73

What is the E of a voltaic cell based on this reaction? 2Ce⁴⁺ + Ni → 2Ce³⁺ + Ni²⁺

A) 2.36 V
B) 2.11 V
C) 6.44 V
D) 0.403 V
E) 1.86 V

Question 74

Describe a voltaic cell.

Question 75

In compounds, fluorine is assigned a −1 oxidation number; oxygen is usually assigned a −2 oxidation number [except in peroxide compounds (where it is −1) and in binary compounds with fluorine (where it is positive)]; and hydrogen is usually assigned a +1 oxidation number [except when it exists as the hydride ion (H⁻), in which case rule 2 prevails].

Question 76

In compounds, all other atoms are assigned an oxidation number so that the sum of the oxidation numbers on all the atoms in the species equals the charge on the species (which is zero if the species is neutral).

Question 77

What is the half reaction for the electrolysis of elemental fluorine?

A) F²⁺ + 2e⁻ → F
B) F⁺ + e⁻ → F
C) F³⁺+ 3e⁻ →F
D) F₂ → 2F⁻ + 2e⁻
E) 2F⁻ $\rightarrow$ F₂ + 2e⁻

Question 78

Define oxidation, reduction, and oxidation-reduction reactions.

Question 79

What is the E of a voltaic cell based on this reaction? NO₃⁻ + 4H⁺ + Fe²⁺ → NO + 2H₂O + Fe³⁺

A) +0.21 V
B) +0.77 V
C) -0.77 V
D) -0.73 V
E) +0.35 V

Question 80

Atoms in their elemental state are assigned an oxidation number of 0.