Electrochemistry Quiz on Mass and Charge Transfer
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Questions and Answers

What is involved in the mass transfer step to the cathode?

  • Transfer of ions from the bulk of solution to the electrode surface (correct)
  • Transfer of electrons from the bulk to the electrode surface
  • Transfer of Cu* from the electrode surface to the solution
  • Transfer of Zn* from the cathode to the anode

What characterizes the charge transfer step?

  • Movement of ions from the anode to the cathode
  • Transfer of heat during the reaction
  • Redox reaction occurring at the electrode surface (correct)
  • Diffusion of ions through the electrolyte

What is the process of transferring Zn* from the anode to the solution called?

  • Mass transfer step (correct)
  • Charge transfer step
  • Electrolytic step
  • Cation exchange process

Which statement best describes the diffusion layer in these processes?

<p>It facilitates the transfer of ions between the bulk and the electrode surface. (C)</p> Signup and view all the answers

Which ion is specifically mentioned as moving from the bulk solution to the cathode?

<p>Cu* (D)</p> Signup and view all the answers

What effect does increasing polarization have on the corrosion rate?

<p>It decreases the corrosion rate. (B)</p> Signup and view all the answers

What is passivity in metals and alloys?

<p>The formation of a protective film. (A)</p> Signup and view all the answers

For a passive layer to be protective, what characteristic is essential?

<p>It must be adherent and non-porous. (A)</p> Signup and view all the answers

Why is chromium added to iron in the production of stainless steel?

<p>To promote the formation of oxide layers. (A)</p> Signup and view all the answers

What type of corrosion is characterized by a general attack across the entire surface?

<p>General corrosion. (D)</p> Signup and view all the answers

What is a necessary condition for the passive layer formed during passivity?

<p>It should be dense and compact. (C)</p> Signup and view all the answers

Which factor does NOT influence the corrosion rate?

<p>Color of the metal (A)</p> Signup and view all the answers

What does polarization relate to in the context of corrosion?

<p>It is inversely proportional to corrosion rate. (D)</p> Signup and view all the answers

What happens to the corrosion rate as temperature increases?

<p>It increases (C)</p> Signup and view all the answers

Which of the following materials is known to form oxide layers contributing to passivity?

<p>Aluminum. (C)</p> Signup and view all the answers

Which phenomenon describes corrosion occurring between dissimilar metals?

<p>Galvanic corrosion (A)</p> Signup and view all the answers

What role does the metal surface condition play in corrosion?

<p>More roughness leads to more corrosion (A)</p> Signup and view all the answers

Which factor is NOT associated with galvanic corrosion?

<p>Temperature of the environment (D)</p> Signup and view all the answers

In which conditions is galvanic corrosion most likely to occur?

<p>When dissimilar metals are connected in the presence of an electrolyte (D)</p> Signup and view all the answers

Which of the following contributes to the extent of corrosion over time?

<p>Time of exposure to corrosive conditions (C)</p> Signup and view all the answers

What does an increase in exposure time do to corrosion?

<p>It increases the extent of corrosion (D)</p> Signup and view all the answers

What is the standard reduction potential for copper?

<p>+0.34 V (A)</p> Signup and view all the answers

Which ion has a greater tendency to be oxidized?

<p>Zn (D)</p> Signup and view all the answers

If the standard reduction potential for zinc is -0.76 V, what is the standard oxidation potential for zinc?

<p>+0.76 V (C)</p> Signup and view all the answers

Which statement accurately describes the tendency of reduction for Cu and Zn?

<p>Cu has a greater tendency to be reduced than Zn. (D)</p> Signup and view all the answers

What would the standard reduction potential for zinc indicate about its reactivity compared to copper?

<p>Zinc is more reactive than copper. (C)</p> Signup and view all the answers

How are the values of standard oxidation potentials related to standard reduction potentials?

<p>They are opposite in sign. (C)</p> Signup and view all the answers

What is the standard reduction potential of Zn when the concentrations of ions are at 1.0 M?

<p>-0.76 V (A)</p> Signup and view all the answers

Which statement is true regarding the tendency of reduction and oxidation for the elements discussed?

<p>Zn has a greater tendency to be oxidized than Cu. (C)</p> Signup and view all the answers

What is the standard electrode potential for lithium in this table?

<p>-3.05 V (A)</p> Signup and view all the answers

Which metal has the most positive standard electrode potential in the given data?

<p>Gold (D)</p> Signup and view all the answers

In the anodic reaction for zinc, which species is being oxidized?

<p>Zn (A)</p> Signup and view all the answers

What is the standard electrode potential for platinum?

<p>+1.20 V (B)</p> Signup and view all the answers

Which of the following reactions indicates corrosion?

<p>Zn + 2e → Zn2+ (D)</p> Signup and view all the answers

What is the relationship of the reduction potentials when discussing corrosion protection?

<p>The metal with higher potential protects the metal with lower potential. (D)</p> Signup and view all the answers

Which element has the lowest reduction potential in the table?

<p>Nickel (C)</p> Signup and view all the answers

The cathodic reaction for iron involves which species?

<p>Fe2+ + 2e (C)</p> Signup and view all the answers

What is the significance of the half-reaction of copper in corrosion processes?

<p>It demonstrates a positive reduction potential. (C)</p> Signup and view all the answers

How does the standard reduction potential of lead compare to that of zinc?

<p>Lead has a less negative potential than zinc. (B)</p> Signup and view all the answers

What is localized corrosion primarily characterized by?

<p>Corrosion occurring within specific crevices or holes (D)</p> Signup and view all the answers

Which type of localized corrosion is known for creating small holes in metal surfaces?

<p>Pitting corrosion (B)</p> Signup and view all the answers

What primarily accelerates the rate of pitting corrosion?

<p>Stagnant solutions (A)</p> Signup and view all the answers

In pitting corrosion, what happens to the area with less oxygen?

<p>It becomes anodic (A)</p> Signup and view all the answers

Which of the following statements is true regarding the conditions that favor pitting corrosion?

<p>Lack of oxygen in a small area contributes to pitting corrosion (C)</p> Signup and view all the answers

What is a common form of localized corrosion in addition to pitting corrosion?

<p>Erosion corrosion (D)</p> Signup and view all the answers

Why is pitting corrosion considered highly destructive?

<p>It compromises the structural integrity of the metal (B)</p> Signup and view all the answers

What is a potential preventive measure for minimizing pitting corrosion?

<p>Sealing off crevices and holes (A)</p> Signup and view all the answers

Flashcards

Mass Transfer Step

The movement of ions from the bulk of the solution to the electrode surface.

Diffusion Layer

The layer surrounding the electrode where ions are transferred through.

Charge Transfer Step

The process where electrons are transferred between ions and the electrode's surface.

Anode

Electrode where oxidation occurs, losing electrons.

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Cathode

Electrode where reduction occurs, gaining electrons.

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Standard Reduction Potential (E°)

The tendency for a species to gain electrons and be reduced, measured in volts.

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Electromotive Force (emf)

The difference in potential between two electrodes in an electrochemical cell.

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Electromotive Force (emf) Series

A series that ranks different species by their standard reduction potential.

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Mass Transfer Step in Electrochemical Reaction

The movement of ions from the bulk of the solution to the electrode surface.

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Diffusion Layer in Electrochemical Reaction

The layer surrounding the electrode where ions are transferred through.

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Charge Transfer Step in Electrochemical Reaction

The process where electrons are transferred between ions and the electrode's surface.

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Standard Electrode Potential (E°)

A measure of the tendency of a chemical species to gain electrons and be reduced. It represents the difference in electrical potential between a half-cell and a standard hydrogen electrode.

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Redox Reaction

A chemical reaction that involves the transfer of electrons from one species to another.

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Galvanic Cell

A type of electrochemical cell that uses a spontaneous chemical reaction to generate an electric current.

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Electrolytic Cell

A type of electrochemical cell that uses an external source of electrical energy to drive a non-spontaneous chemical reaction.

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Oxidation

The process of losing electrons by a species.

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Reduction

The process of gaining electrons by a species.

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Cell Potential (Ecell)

The difference in electrical potential between two half-cells in an electrochemical cell. It determines the direction of electron flow and the overall voltage of the cell.

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Cathodic Reaction

The reaction that occurs at the electrode with a higher standard electrode potential.

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Polarization and Corrosion

The tendency for a metal to resist corrosion increases as polarization increases.

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Passivity

A phenomenon where certain metals form a thin protective layer on their surface, making them resistant to corrosion.

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Corrosion

Refers to the chemical reactions that occur at the surface of a metal when it is exposed to a corrosive environment.

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Polarization

A measure of the difference in electrical potential between the metal and the surrounding environment.

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General Corrosion

A type of corrosion that affects the entire surface of a metal.

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Localized Corrosion

A type of corrosion that occurs at specific locations on a metal surface.

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Passive Metal

A metal that has a thin protective layer on its surface, making it resistant to corrosion.

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Active Metal

A metal that is more likely to corrode, usually because it lacks a protective layer.

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Corrosion Rate

The rate at which a metal corrodes, influenced by factors like the type of metal, environment, temperature, and surface condition.

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Galvanic Corrosion

A type of corrosion that occurs when two different metals are connected in the presence of an electrolyte. The difference in their electrical potentials causes one metal to corrode faster.

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Potential Difference

The difference in electrical potential between the anode and cathode in galvanic corrosion.

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Distance Between Anode and Cathode

The distance between the anode and cathode in galvanic corrosion.

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Cathode/Anode (CIA) Area Ratio

The ratio of the surface area of the cathode to the anode in galvanic corrosion.

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Factors Affecting Galvanic Corrosion

The factors that influence galvanic corrosion.

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Pitting Corrosion

A type of corrosion that occurs in localized areas, forming small holes or pits on the metal surface.

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Erosion Corrosion

This type of corrosion is related to the flow of fluids, leading to wear and tear on the metal surface.

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Oxygen Depletion in Pitting Corrosion

The area lacking oxygen becomes the anode, while the area with excess oxygen becomes the cathode.

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Stagnant Solutions and Pitting Corrosion

Still, non-moving solutions contribute to faster pitting corrosion, as they allow the oxygen concentration difference to increase between areas.

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Intergranular Corrosion

This form of corrosion forms when a material interacts with another substance, leading to the formation of a layer on the surface.

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Stress Corrosion Cracking

This form of corrosion involves the formation of cracks in the metal caused by repeated stress.

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Hydrogen Embrittlement

This type of corrosion is caused by a build-up of stress in the metal during the manufacturing process.

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Study Notes

Introduction to Corrosion

  • Corrosion is the irreversible damage of metals due to reactions with their surroundings.
  • The reaction produces oxides or salts of the original metal.

Steps of Electrochemical Reactions

  • Mass Transfer Step: Ions move from the bulk solution to the electrode surface through a diffusion layer. (e.g., Cu2+ from bulk solution to the cathode.)
  • Charge Transfer Step: Redox reactions between ions and electrons occur at the electrode surface.
  • Mass Transfer Step (2): Ions move from the electrode surface to the bulk solution through a diffusion layer. (e.g., Zn2+ from the anode to the bulk solution.)

Redox Reactions

  • A redox reaction involves both oxidation and reduction half-reactions, with a transfer of electrons.
  • The species that loses electrons is oxidized; the species that gains electrons is reduced.
    • Example: Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
      • Zn is the reducing agent (causes Cu2+ to be reduced)
      • Cu2+ is the oxidizing agent (causes Zn to be oxidized)
  • The tendency of a reduction to occur is measured by its reduction potential (E°), measured in volts.

Standard Reduction Potentials

  • Standard reduction potentials are measured at standard conditions (25°C and 1.0 M ion concentrations).
  • Higher positive or lower negative reduction potential values indicate a greater tendency for the reduction reaction to occur.
  • Example: Copper (Cu2+) has a higher reduction potential (+0.34 V) than zinc (Zn2+) (-0.76V)

Costs of Corrosion

  • Direct Economic Losses: Replacement of corroded structures and extra costs of corrosion inhibitors.
  • Indirect Costs: Loss of products (e.g., due to leaks), loss of production time, loss of efficiency, and product contamination.

Polarization

  • Polarization decreases the efficiency of an electrochemical reaction by disturbing equilibrium.
  • Two types of polarization are concentration and activation.
  • Polarization is inversely proportional to the corrosion rate. Increased polarization decreases corrosion.

Passivity

  • Some metals and alloys become passive under specific environmental conditions.
  • Passivity is the formation of a thin, protective film (1-10 nm thick) on metal surfaces due to reaction with the surrounding environment.

Types of Corrosion

  • General (Uniform) Corrosion: A uniform rate of metal damage over the entire exposed surface area (example: rusting).
  • Localized Corrosion: Damage within localized areas like crevices or holes. Two types are:
    • Pitting Corrosion: Highly destructive, localized holes in the metal surface (pitting). This is often associated with a lack of oxygen in a small area.
    • Erosion Corrosion: Accelerated corrosion due to the movement of a corrosive fluid over exposed metal surfaces.

Corrosion Protection and Control

  • Material Selection: Choose materials resistant to the specific environment.
  • Design Modifications: Design systems to minimize corrosive conditions.
  • Changing the Environment: Change the environment to reduce corrosion factors, such as manipulating pH.
  • Changing Metal Potential: Use anodic or cathodic protection to modify metal potential.
  • Protective Coatings: Applying coatings like paints, plastics, zinc or tin.

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Description

Test your understanding of the mass transfer and charge transfer steps involved in electrochemical processes. This quiz covers key concepts such as the transfer of ions to the cathode, diffusion layers, and reaction mechanisms. Perfect for students studying electrochemistry!

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