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My MCAT to memorize > Gen Chem - Redox and Electrochemistry > Flashcards

Gen Chem - Redox and Electrochemistry Flashcards

1
Q

What is the oxidation number of a free element?

A

The oxidation number of a free element is zero.

For example, the atoms in N2, P4, Sg, and He all have oxidation numbers of zero.

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2
Q

What is the oxidation number for a monatomic ion?

A

The oxidation number for a monatomic ion is equal to the charge of the ion.

For example, the oxidation numbers for Na+, Cu+, Fe3+, Cl-, and N3- are +1, +2, +3, -1, and -3, respectively.

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3
Q

What is the oxidation number of Group IA elements in a compound?

A

The oxidation number of each Group IA element in a compound is +1.

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4
Q

What is the oxidation number of Group IIA elements in a compound?

A

The oxidation number of each Group IIA element in a compound is +2.

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5
Q

What is the oxidation number of Group VIIA (halogens) elements in a compound?

A

The oxidation number of each Group VIIA element in a compound is -1, except when combined with an element of higher electronegativity.

For example, in HCl, the oxidation number of Cl is -1; in HOCl, however, the oxidation number of Cl is +1.

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6
Q

What is the usual oxidation number of hydrogen?

A

The oxidation number of hydrogen is usually +1; however, it is -1 in compounds with less electronegative elements (Groups IA and IIA).

Hydrogen is +1 in HCl, but -1 in NaH.

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7
Q

What is the oxidation number of oxygen in most compounds?

A

In most compounds, the oxidation number of oxygen is -2.

The exceptions are peroxides (O2^2-), where each oxygen is -1, and compounds with more electronegative elements, such as OF2, where oxygen has a +2 charge.

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8
Q

What is the sum of the oxidation numbers in a neutral compound?

A

The sum of the oxidation numbers of all the atoms present in a neutral compound is zero.

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9
Q

What is the sum of the oxidation numbers in a polyatomic ion?

A

The sum of the oxidation numbers of the atoms present in a polyatomic ion is equal to the charge of the ion.

Thus, for SO4^2-, the sum of the oxidation numbers must be -2.

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10
Q

How can you think of the oxidation number?

A

Think of the oxidation number as the typical charge of an element based on its atomic number metallicity.

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11
Q

What are oxidizing agents?

A

Substances that gain electrons in a chemical reaction

Examples include F2, Cl2, Br2, I2 (halogens), H2SO4, and KMnO4.

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12
Q

What are reducing agents?

A

Substances that lose electrons in a chemical reaction

Examples include Sn2+, pure metals, and NaBH4.

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13
Q

List three examples of halogen oxidizing agents.

A
  • F2
  • Cl2
  • Br2
  • I2
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14
Q

What is the chemical formula for sulfuric acid?

A

H2SO4

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15
Q

What type of substance is hydrazine?

A

A reducing agent

Commonly used in various chemical reactions.

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16
Q

What is the role of NaClO in chemical reactions?

A

Acts as an oxidizing agent

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17
Q

What is the significance of Zn (Hg) in organic chemistry?

A

Used as a reducing agent

Often utilized in reduction reactions.

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18
Q

What is Lindlar’s catalyst used for?

A

Facilitates hydrogenation reactions

Commonly used to convert alkynes to alkenes.

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19
Q

What does CrO3 indicate in chemical reactions?

A

An oxidizing agent

Often used in oxidation reactions.

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20
Q

What does NaBH4 stand for?

A

Sodium borohydride

A common reducing agent in organic synthesis.

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21
Q

What are NAD+ and FADH2 classified as?

A

Coenzymes that act as electron carriers

Involved in cellular respiration.

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22
Q

Fill in the blank: F2, Cl2, Br2, and I2 are examples of _______.

A

oxidizing agents

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23
Q

What is the function of LiAlH4 in chemical reactions?

A

Acts as a strong reducing agent

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24
Q

What does PCC stand for?

A

Pyridinium chlorochromate

Used for oxidation of alcohols.

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25
Q

True or False: HNO3 is an oxidizing agent.

A

True

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26
Q

What do NADH and FADH2 represent?

A

Reduced forms of NAD+ and FAD

Play key roles in metabolic pathways.

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27
Q

What is oxidation in the context of redox reactions?

A

A loss of electrons

Oxidation refers to the process where an atom, ion, or molecule loses electrons.

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28
Q

What is reduction in the context of redox reactions?

A

A gain of electrons

Reduction involves the gain of electrons by an atom, ion, or molecule.

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29
Q

What is a redox reaction?

A

An oxidation-reduction reaction

Redox reactions involve the transfer of electrons between two species.

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30
Q

What role does an oxidizing agent play in a redox reaction?

A

Facilitates the oxidation of another compound and is reduced itself

The oxidizing agent accepts electrons during the reaction.

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31
Q

What role does a reducing agent play in a redox reaction?

A

Facilitates the reduction of another compound and is oxidized itself

The reducing agent donates electrons during the reaction.

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32
Q

Fill in the blank: Common oxidizing agents almost all contain _______.

A

[oxygen or a similarly electronegative element]

This characteristic allows them to accept electrons easily.

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33
Q

Fill in the blank: Common reducing agents often contain _______.

A

[metal ions or hydrides (HT)]

These substances are prone to lose electrons easily.

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34
Q

What is the most common method for balancing redox reactions?

A

Half-reaction method (ion-electron method)

This method involves separating and balancing two half-reactions.

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35
Q

What is the first step in balancing redox reactions using the half-reaction method?

A

Separate the two half-reactions

This allows for individual balancing of each half-reaction.

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36
Q

When balancing redox reactions, which elements should be balanced first?

A

All elements besides H and O

This prioritization helps simplify the balancing process.

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37
Q

In acidic solutions, how should H and O be balanced?

A

Using water and H+

Water is added to balance oxygen, and H+ ions are used to balance hydrogen.

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38
Q

In basic solutions, how should H and O be balanced?

A

Using water and OH-

Hydroxide ions are used to balance hydrogen in basic conditions.

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39
Q

What is the purpose of adding electrons in balancing half-reactions?

A

To balance the charges of each half-reaction

Electrons are added to one side of the reaction as needed.

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40
Q

What must be done to the half-reactions to balance the number of electrons?

A

Multiply the half-reactions as necessary

This ensures both half-reactions have the same number of electrons.

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41
Q

What is the final step after adding the half-reactions?

A

Confirm that the mass and charge are balanced

This verification is crucial to ensure the reaction is correctly balanced.

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42
Q

What does a complete ionic equation account for?

A

All of the ions present in a reaction

Aqueous compounds are split into their relevant ions while solid salts remain intact.

43
Q

What do net ionic equations ignore?

A

Spectator ions

These are the ions that do not participate in the reaction.

44
Q

How is a net ionic reaction obtained?

A

Subtract the ions appearing on both sides of the reaction

This process removes spectator ions from the complete ionic equation.

45
Q

What is generally true about net ionic equations for reactions with no aqueous salts?

A

They are the same as the overall balanced reaction

This indicates that all species are involved in the reaction.

46
Q

What is true about double displacement (metathesis) reactions that do not form a solid salt?

A

There is no net ionic reaction

In such cases, all ions remain in solution and do not change oxidation number.

47
Q

What is the most common method for balancing redox reactions?

A

Half-reaction method (ion-electron method)

This method involves separating and balancing two half-reactions.

48
Q

What is the first step in balancing redox reactions using the half-reaction method?

A

Separate the two half-reactions

This allows for individual balancing of each half-reaction.

49
Q

When balancing redox reactions, which elements should be balanced first?

A

All elements besides H and O

This prioritization helps simplify the balancing process.

50
Q

In acidic solutions, how should H and O be balanced?

A

Using water and H+

Water is added to balance oxygen, and H+ ions are used to balance hydrogen.

51
Q

In basic solutions, how should H and O be balanced?

A

Using water and OH-

Hydroxide ions are used to balance hydrogen in basic conditions.

52
Q

What is the purpose of adding electrons in balancing half-reactions?

A

To balance the charges of each half-reaction

Electrons are added to one side of the reaction as needed.

53
Q

What must be done to the half-reactions to balance the number of electrons?

A

Multiply the half-reactions as necessary

This ensures both half-reactions have the same number of electrons.

54
Q

What is the final step after adding the half-reactions?

A

Confirm that the mass and charge are balanced

This verification is crucial to ensure the reaction is correctly balanced.

55
Q

What does a complete ionic equation account for?

A

All of the ions present in a reaction

Aqueous compounds are split into their relevant ions while solid salts remain intact.

56
Q

What do net ionic equations ignore?

A

Spectator ions

These are the ions that do not participate in the reaction.

57
Q

How is a net ionic reaction obtained?

A

Subtract the ions appearing on both sides of the reaction

This process removes spectator ions from the complete ionic equation.

58
Q

What is generally true about net ionic equations for reactions with no aqueous salts?

A

They are the same as the overall balanced reaction

This indicates that all species are involved in the reaction.

59
Q

What is true about double displacement (metathesis) reactions that do not form a solid salt?

A

There is no net ionic reaction

In such cases, all ions remain in solution and do not change oxidation number.

60
Q

What are electrochemical cells?

A

Contained systems in which oxidation-reduction reactions occur

Electrochemical cells convert chemical energy into electrical energy and vice versa.

61
Q

What are the three fundamental types of electrochemical cells?

A

Galvanic cells, electrolytic cells, concentration cells

Galvanic cells are also known as voltaic cells.

62
Q

What type of reactions do galvanic cells and concentration cells house?

A

Spontaneous reactions

These reactions occur naturally without external energy input.

63
Q

What type of reactions do electrolytic cells contain?

A

Nonspontaneous reactions

These reactions require external energy to occur.

64
Q

What does the change in Gibbs free energy (ΔG) indicate about spontaneity?

A

ΔG < 0 indicates spontaneity; ΔG > 0 indicates nonspontaneity

Spontaneous reactions release energy, while nonspontaneous reactions absorb energy.

65
Q

What are the electrodes in electrochemical cells where oxidation and reduction occur called?

A

Anode (oxidation) and cathode (reduction)

The anode is where electrons are lost, and the cathode is where electrons are gained.

66
Q

What does electromotive force (emf) correspond to in electrochemical cells?

A

Voltage or electrical potential difference of the cell

Emf reflects the capacity of the cell to do electrical work.

67
Q

What does a positive emf indicate about an electrochemical cell?

A

The cell is able to release energy (ΔG < 0), meaning it is spontaneous

Positive emf indicates that the cell can perform work.

68
Q

What does a negative emf indicate about an electrochemical cell?

A

The cell must absorb energy (ΔG > 0), meaning it is nonspontaneous

Negative emf indicates that the cell cannot perform work without external energy.

69
Q

What are electrochemical cells?

A

Contained systems in which oxidation-reduction reactions occur

Electrochemical cells convert chemical energy into electrical energy and vice versa.

70
Q

What are the three fundamental types of electrochemical cells?

A

Galvanic cells, electrolytic cells, concentration cells

Galvanic cells are also known as voltaic cells.

71
Q

What type of reactions do galvanic cells and concentration cells house?

A

Spontaneous reactions

These reactions occur naturally without external energy input.

72
Q

What type of reactions do electrolytic cells contain?

A

Nonspontaneous reactions

These reactions require external energy to occur.

73
Q

What does the change in Gibbs free energy (ΔG) indicate about spontaneity?

A

ΔG < 0 indicates spontaneity; ΔG > 0 indicates nonspontaneity

Spontaneous reactions release energy, while nonspontaneous reactions absorb energy.

74
Q

What are the electrodes in electrochemical cells where oxidation and reduction occur called?

A

Anode (oxidation) and cathode (reduction)

The anode is where electrons are lost, and the cathode is where electrons are gained.

75
Q

What does electromotive force (emf) correspond to in electrochemical cells?

A

Voltage or electrical potential difference of the cell

Emf reflects the capacity of the cell to do electrical work.

76
Q

What does a positive emf indicate about an electrochemical cell?

A

The cell is able to release energy (ΔG < 0), meaning it is spontaneous

Positive emf indicates that the cell can perform work.

77
Q

What does a negative emf indicate about an electrochemical cell?

A

The cell must absorb energy (ΔG > 0), meaning it is nonspontaneous

Negative emf indicates that the cell cannot perform work without external energy.

78
Q

What is the free energy change that represents a non-spontaneous reaction?

79
Q

What does the Nernst equation calculate?

A

The emf of a cell under nonstandard conditions.

80
Q

What is the relationship between emf and ionic concentrations in electrochemical cells?

A

Emf varies with the changing concentrations of the species in the cell.

81
Q

What is the standard form of the Nernst equation?

A

Ecell = E°cell - (RT/nF) ln Q

82
Q

In the simplified Nernst equation, what assumption is made about temperature?

83
Q

What is the simplified version of the Nernst equation?

A

Ecell = E°cell - (0.0592/n) log Q

84
Q

What variables are represented in the Nernst equation?

A
  • Ecell
  • E°cell
  • R (ideal gas constant)
  • T (temperature in kelvin)
  • n (number of moles of electrons)
  • F (Faraday constant)
  • Q (reaction quotient)
85
Q

True or False: The emf of a cell is constant regardless of conditions.

86
Q

Fill in the blank: The reaction quotient, Q, is used in the Nernst equation to account for _______.

A

[the concentration of ions in the cell]

87
Q

What does a concentration cell require for a measurable voltage and current?

A

Different concentrations of ions in the two compartments.

88
Q

What is the free energy change that represents a non-spontaneous reaction?

89
Q

What does the Nernst equation calculate?

A

The emf of a cell under nonstandard conditions.

90
Q

What is the relationship between emf and ionic concentrations in electrochemical cells?

A

Emf varies with the changing concentrations of the species in the cell.

91
Q

What is the standard form of the Nernst equation?

A

Ecell = E°cell - (RT/nF) ln Q

92
Q

In the simplified Nernst equation, what assumption is made about temperature?

93
Q

What is the simplified version of the Nernst equation?

A

Ecell = E°cell - (0.0592/n) log Q

94
Q

What variables are represented in the Nernst equation?

A
  • Ecell
  • E°cell
  • R (ideal gas constant)
  • T (temperature in kelvin)
  • n (number of moles of electrons)
  • F (Faraday constant)
  • Q (reaction quotient)
95
Q

True or False: The emf of a cell is constant regardless of conditions.

96
Q

Fill in the blank: The reaction quotient, Q, is used in the Nernst equation to account for _______.

A

[the concentration of ions in the cell]

97
Q

What does a concentration cell require for a measurable voltage and current?

A

Different concentrations of ions in the two compartments.

98
Q

How can AG° be determined?

A

AG° can be determined using the equation: AG° = -RT ln Keq

Where R is the ideal gas constant, T is the absolute temperature, and Keq is the equilibrium constant for the reaction.

99
Q

What is the relationship between AG°, E° cell, and Keq?

A

AG° = -nFE° cell = -RT ln Keq

This shows that the standard free energy change is related to both the cell potential and the equilibrium constant.

100
Q

What variables are needed to calculate E° cell?

A

Values for n, T, and Keq are needed to calculate E° cell

n is the number of moles of electrons transferred, T is the temperature in Kelvin, and Keq is the equilibrium constant.

101
Q

What can be inferred about logarithm values in relation to equilibrium constants?

A

A logarithm will be positive when equilibrium constants are greater than 1

This indicates that the reaction favors the products at equilibrium.

102
Q

Is it necessary to calculate natural logarithm values on the MCAT?

A

No, you will not be expected to calculate natural logarithm values in your head

However, understanding the concepts behind these equations is important for the exam.

103
Q

Fill in the blank: AG° can also be expressed as _______.

A

AG° = -RT ln Keq

104
Q

True or False: AG° and E° cell are inversely related.

A

True

As one increases, the other decreases, indicating a relationship between free energy and cell potential.

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