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Questions and Answers
In a redox reaction, what characterizes the standard electrode potential (E°)?
In a redox reaction, what characterizes the standard electrode potential (E°)?
- It refers to the half-reaction written as reduction. (correct)
- It is independent of the half-reaction.
- It refers to the half-reaction written as oxidation.
- It indicates the overall reaction potential.
Which of the following statements accurately describes a scenario with a more positive standard electrode potential (E°)?
Which of the following statements accurately describes a scenario with a more positive standard electrode potential (E°)?
- It indicates an anode where oxidation occurs, leading to a lesser attraction for electrons.
- It indicates a reducing agent that promotes oxidation in other species.
- It indicates a cathode where reduction occurs, leading to a greater attraction for electrons. (correct)
- It indicates a reducing agent with lesser electron affinity.
Which statement correctly describes a scenario with a less positive standard electrode potential (E°)?
Which statement correctly describes a scenario with a less positive standard electrode potential (E°)?
- It favors reduction reactions, inhibiting the oxidation of other species.
- It signifies an anode where oxidation occurs, leading to a greater repulsion of electrons from the species. (correct)
- It indicates an oxidizing agent with a strong tendency to accept electrons.
- It signifies a cathode where reduction occurs, leading to a greater attraction for electrons of another species.
In the context of standard electrode potentials, what does a strong oxidizing agent typically exhibit?
In the context of standard electrode potentials, what does a strong oxidizing agent typically exhibit?
MnO4- is a strong oxidizing agent. According to the provided data, which of the following ions can MnO4- oxidize in acidic media?
MnO4-/Mn2+ = +1.51 V
Fe3+/Fe2+ = +0.77
Cl2/Cl- = +1.36 V
Ce4+/Ce3+ = +1.76 V
MnO4- is a strong oxidizing agent. According to the provided data, which of the following ions can MnO4- oxidize in acidic media?
MnO4-/Mn2+ = +1.51 V
Fe3+/Fe2+ = +0.77
Cl2/Cl- = +1.36 V
Ce4+/Ce3+ = +1.76 V
Which method primarily uses a more active metal to prevent corrosion of a less active metal?
Which method primarily uses a more active metal to prevent corrosion of a less active metal?
In sacrificial anode cathodic protection, how do free electrons prevent corrosion at the cathode (steel)?
In sacrificial anode cathodic protection, how do free electrons prevent corrosion at the cathode (steel)?
What is the defined standard condition for the concentration of all dissolved substances when determining standard cell potential?
What is the defined standard condition for the concentration of all dissolved substances when determining standard cell potential?
How does the reaction quotient (Q) relate to predicting the direction of a reaction under nonstandard conditions?
How does the reaction quotient (Q) relate to predicting the direction of a reaction under nonstandard conditions?
According to the Nernst equation, what is the state of a battery when Ecell equals 0?
According to the Nernst equation, what is the state of a battery when Ecell equals 0?
How does the influence of pH on redox stability affect the cell potential (Ecell)?
How does the influence of pH on redox stability affect the cell potential (Ecell)?
What is the effect of increased acidity on the oxidizing strength of the perchlorate anion (ClO4-)?
What is the effect of increased acidity on the oxidizing strength of the perchlorate anion (ClO4-)?
What is the condition to make water act as an oxidizing agent?
What is the condition to make water act as an oxidizing agent?
What condition promotes the passivation of metals reacting with water?
What condition promotes the passivation of metals reacting with water?
During the anodizing of aluminum, what is the primary purpose of the electrolytic process?
During the anodizing of aluminum, what is the primary purpose of the electrolytic process?
In a disproportionation reaction, what happens to the oxidation number of an element?
In a disproportionation reaction, what happens to the oxidation number of an element?
What happens when two species of the same element in different oxidation states form a product in which the element is in the same oxidation state?
What happens when two species of the same element in different oxidation states form a product in which the element is in the same oxidation state?
In a Latimer diagram, how are the oxidation states arranged?
In a Latimer diagram, how are the oxidation states arranged?
How can the standard potential of a couple that is the combination of two other couples be obtained?
How can the standard potential of a couple that is the combination of two other couples be obtained?
What does a Frost diagram depict?
What does a Frost diagram depict?
In a Frost diagram, what does the slope of the line connecting two points represent?
In a Frost diagram, what does the slope of the line connecting two points represent?
According to Frost Diagrams, what characteristic defines a species that is unstable to disproportionation?
According to Frost Diagrams, what characteristic defines a species that is unstable to disproportionation?
Based on potential data from Frost Diagrams, what process will occur if two species have an intermediate species that lies below the straight line joining them?
Based on potential data from Frost Diagrams, what process will occur if two species have an intermediate species that lies below the straight line joining them?
What information does a Pourbaix diagram provide?
What information does a Pourbaix diagram provide?
How do sloped lines in a Pourbaix diagram relate different chemical species?
How do sloped lines in a Pourbaix diagram relate different chemical species?
Regarding iron, under what conditions is it most likely to corrode according to a Pourbaix diagram?
Regarding iron, under what conditions is it most likely to corrode according to a Pourbaix diagram?
What is the Ellingham diagram primarily used to analyze?
What is the Ellingham diagram primarily used to analyze?
According to the Ellingham diagram, under what conditions does carbon typically reduce a metal oxide to its metal form?
According to the Ellingham diagram, under what conditions does carbon typically reduce a metal oxide to its metal form?
In the Hall-Heroult process for aluminum production, what is the role of cryolite?
In the Hall-Heroult process for aluminum production, what is the role of cryolite?
In both electrochemical cells and the clarification, does E°cell use oxidation or reduction in order to proceed with solving the equation?
In both electrochemical cells and the clarification, does E°cell use oxidation or reduction in order to proceed with solving the equation?
Following the steps of E°cell, what follows after you extract E°Cell?
Following the steps of E°cell, what follows after you extract E°Cell?
Which of the following metals is more likely to form a passivating oxide layer in water?
Which of the following metals is more likely to form a passivating oxide layer in water?
Considering the Nernst equation under non-standard conditions, how is the cell-potential affected by changes in temperature?
Considering the Nernst equation under non-standard conditions, how is the cell-potential affected by changes in temperature?
What primarily influences whether water acts as an oxidizing or reducing agent in a redox reaction?
What primarily influences whether water acts as an oxidizing or reducing agent in a redox reaction?
Given the electrochemical series, which metal would you choose as a sacrificial anode to protect steel from corrosion in seawater?
Given the electrochemical series, which metal would you choose as a sacrificial anode to protect steel from corrosion in seawater?
How do standard conditions (1M, 1 Barr, 298K) differ from non-standard conditions in electrochemical reactions?
How do standard conditions (1M, 1 Barr, 298K) differ from non-standard conditions in electrochemical reactions?
How does the Ellingham diagram aid in optimizing steel production processes?
How does the Ellingham diagram aid in optimizing steel production processes?
In what way does increasing the thickness of an oxide layer affect a material's properties?
In what way does increasing the thickness of an oxide layer affect a material's properties?
Flashcards
Standard electrode potential (E°)
Standard electrode potential (E°)
Potential of a half-reaction under standard conditions (1 M, 1 bar, 298 K), written as reduction.
Cathode
Cathode
The electrode where reduction occurs; attracts electrons.
Anode
Anode
The electrode where oxidation occurs; repels electrons.
Standard cell potential (E°cell)
Standard cell potential (E°cell)
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Ecell
Ecell
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n
n
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Reaction quotient (Q)
Reaction quotient (Q)
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Reaction at equilibrium
Reaction at equilibrium
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Latimer Diagram
Latimer Diagram
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Frost Diagram
Frost Diagram
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Pourbaix Diagram
Pourbaix Diagram
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Anodizing
Anodizing
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Disproportionation
Disproportionation
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Ellingham Diagram
Ellingham Diagram
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E cell = 0
E cell = 0
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Study Notes
- A standard electrode potential (E°) always refers to the half-reaction written as reduction.
- The reaction for standard electrode potential is Mx+(aq) + x e¯ → M(s)
More Positive E°
- The cathode is the site of reduction
- A greater attraction to electrons exists at the cathode
- The species is an oxidizing agent
Less Positive E°
- The anode is the site of oxidation
- A greater repulsion to electrons exists at the anode
- The species is a reducing agent
- As E° becomes more positive, the strength of the oxidizing agent increases and the strength of the reducing agent decreases.
Practice Question: Oxidizing Ions
- MnO₄⁻ is a strong oxidizing agent and can oxidize other ions in acidic media
- MnO₄⁻/Mn²⁺ has a standard potential of +1.51 V
- Fe³⁺/Fe²⁺ has a standard potential of +0.77 V
- Cl₂/Cl⁻ has a standard potential of +1.36 V
- Ce⁴⁺/Ce³⁺ has a standard potential of +1.76 V
- MnO₄⁻ can oxidize Fe²⁺ and Cl⁻, which have less positive standard potentials
- MnO₄⁻ cannot oxidize Ce³⁺
Sacrificial Anode Cathodic Protection (SACP)
- Cathodic protection sacrifices a more active metal to protect a less active metal from corrosion
- Fe/Fe²⁺ has a standard potential of +0.45 V
- Zn/Zn²⁺ has a standard potential of +0.76 V
Sacrificial Anode Cathodic Protection (SACP) Reactions
- The process involves free electrons traveling through a metal path to less active sites
- The reaction at these sites is O₂ + 4e⁻ + 2H₂O → 4 OH⁻
- Recombination of these ions at the surface yields the iron-corrosion product ferrous hydroxide
- The reaction is 2Fe + O₂ + 2H₂O → 2Fe(OH)₂
- In the case of aluminum anodes, the reaction at the aluminum surface is 4Al → 4Al³⁺ + 12 e⁻
- The reaction at the steel surface is 3O₂ + 12e⁻ + 6H₂O → 12OH⁻
- Corrosion does not occur as long as the current (free electrons) arrives at the cathode (steel) faster than oxygen.
Standard Cell Potential
- Standard cell potential (E°cell) refers to cell potential at standard conditions (º)
- Concentration of all dissolved substances is 1 M
- Pressure of all gases is 1 atm
Nernst Equation
- Equation: Ecell = E°cell - (RT/nF)lnQ
- Ecell represents the cell potential under nonstandard conditions
- E°cell represents the standard cell potential
- n represents the number of electrons transferred in the balanced redox reaction
- Q represents the reaction quotient, which measures the relative amounts of products and reactants present during a reaction at a particular point in time
- For a reaction aA + bB ⇌ cC + dD, Q = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ
More on the Nernst Equation
- When Q = 1, the system is in standard state, and Ecell = E°cell
- When Q < 1, lnQ < 0, and Ecell > E°cell
- When Q > 1, lnQ > 0, and Ecell < E°cell
- When Q = K, the reaction is at equilibrium, and Ecell = 0
- At reaction equilibrium (Q=Keq), the reaction quotient Q=Keq, ΔG=0, and so E=0
- Transformed Nerst Equation 0= E°cell - (0.0592V/n)logKeq and logKeq = nEo/0.0592V
- K>1 and E°>0 indicates reaction favors products formation.
- K1 and E°
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