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?

It facilitates the transfer of ions between the bulk and the electrode surface. Signup and view all the answers

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

Cu* Signup and view all the answers

What effect does increasing polarization have on the corrosion rate?

It decreases the corrosion rate. Signup and view all the answers

What is passivity in metals and alloys?

The formation of a protective film. Signup and view all the answers

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

It must be adherent and non-porous. Signup and view all the answers

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

To promote the formation of oxide layers. Signup and view all the answers

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

General corrosion. Signup and view all the answers

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

It should be dense and compact. Signup and view all the answers

Which factor does NOT influence the corrosion rate?

Color of the metal Signup and view all the answers

What does polarization relate to in the context of corrosion?

It is inversely proportional to corrosion rate. Signup and view all the answers

What happens to the corrosion rate as temperature increases?

It increases Signup and view all the answers

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

Aluminum. Signup and view all the answers

Which phenomenon describes corrosion occurring between dissimilar metals?

Galvanic corrosion Signup and view all the answers

What role does the metal surface condition play in corrosion?

More roughness leads to more corrosion Signup and view all the answers

Which factor is NOT associated with galvanic corrosion?

Temperature of the environment Signup and view all the answers

In which conditions is galvanic corrosion most likely to occur?

When dissimilar metals are connected in the presence of an electrolyte Signup and view all the answers

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

Time of exposure to corrosive conditions Signup and view all the answers

What does an increase in exposure time do to corrosion?

It increases the extent of corrosion Signup and view all the answers

What is the standard reduction potential for copper?

+0.34 V Signup and view all the answers

Which ion has a greater tendency to be oxidized?

Zn 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?

+0.76 V Signup and view all the answers

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

Cu has a greater tendency to be reduced than Zn. Signup and view all the answers

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

Zinc is more reactive than copper. Signup and view all the answers

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

They are opposite in sign. Signup and view all the answers

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

-0.76 V Signup and view all the answers

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

Zn has a greater tendency to be oxidized than Cu. Signup and view all the answers

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

-3.05 V Signup and view all the answers

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

Gold Signup and view all the answers

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

Zn Signup and view all the answers

What is the standard electrode potential for platinum?

+1.20 V Signup and view all the answers

Which of the following reactions indicates corrosion?

Zn + 2e → Zn2+ Signup and view all the answers

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

The metal with higher potential protects the metal with lower potential. Signup and view all the answers

Which element has the lowest reduction potential in the table?

Nickel Signup and view all the answers

The cathodic reaction for iron involves which species?

Fe2+ + 2e Signup and view all the answers

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

It demonstrates a positive reduction potential. Signup and view all the answers

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

Lead has a less negative potential than zinc. Signup and view all the answers

What is localized corrosion primarily characterized by?

Corrosion occurring within specific crevices or holes Signup and view all the answers

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

Pitting corrosion Signup and view all the answers

What primarily accelerates the rate of pitting corrosion?

Stagnant solutions Signup and view all the answers

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

It becomes anodic Signup and view all the answers

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

Lack of oxygen in a small area contributes to pitting corrosion Signup and view all the answers

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

Erosion corrosion Signup and view all the answers

Why is pitting corrosion considered highly destructive?

It compromises the structural integrity of the metal Signup and view all the answers

What is a potential preventive measure for minimizing pitting corrosion?

Sealing off crevices and holes Signup and view all the answers

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!