Question

Use \(E^{\circ}\) values to predict which of the following metals, if coated on nickel, will provide cathodic protection against corrosion to nickel. (a) Cu (b) \(\mathrm{Mg}\) (c) Zn (d) \(\mathrm{Cr}\)

Short answer

Mg, Zn, and Cr can protect nickel.

Step-by-step solution

Understand the Concept

To determine if a metal can provide cathodic protection for nickel, the metal's standard reduction potential ( E^{ ext{°}} ) must be lower (more negative) than nickel's. This ensures the protecting metal is more likely to oxidize (corrode) instead of nickel.

List Standard Reduction Potentials

Recall or look up the E^{ ext{°}} values for each metal: - Nickel (Ni): -0.25 V - Copper (Cu): +0.34 V - Magnesium (Mg): -2.37 V - Zinc (Zn): -0.76 V - Chromium (Cr): -0.74 V

Compare E° Values with Nickel

Compare the E^{ ext{°}} values of each metal with nickel's: - Copper's E^{ ext{°}} is higher than nickel's, so it cannot provide protection. - Magnesium's E^{ ext{°}} is lower than nickel's, suggesting it can provide protection. - Zinc's E^{ ext{°}} is lower than nickel's, suggesting it can provide protection. - Chromium's E^{ ext{°}} is lower than nickel’s, suggesting it can provide protection.

Conclusion

Based on the E^{ ext{°}} values, magnesium, zinc, and chromium can provide cathodic protection for nickel because their E^{ ext{°}} values are more negative than nickel's.

Key concepts

Standard reduction potential

Standard reduction potential ( E^{ ext{°}} ) is a crucial concept in understanding how chemical reactions, especially redox reactions, work. It is a measure of the tendency of a chemical species to acquire electrons and thus be reduced. Measured in volts (V), it is often determined under standard conditions: 25°C, 1 atm pressure, and with a concentration of 1 M for each species involved.
A more positive E^{ ext{°}} value indicates a greater tendency to gain electrons and undergo reduction, making it a good oxidizing agent. Conversely, a more negative E^{ ext{°}} value suggests a stronger tendency to lose electrons and be oxidized, making it a good reducing agent.
In contexts like cathodic protection, these values help predict which metal will oxidize first. If a metal's standard reduction potential is lower than another, it will act sacrificially by corroding, therefore protecting the second metal.

Corrosion prevention

Corrosion prevention involves techniques to protect metals from degradation due to reactions with their environment. Cathodic protection is a key strategy used here.
In this technique, a more easily oxidized metal is placed in contact with the metal being protected, such as nickel. This sacrificial metal then corrodes in place of the protected metal. To choose the correct sacrificial metal, it must have a standard reduction potential ( E^{ ext{°}} ) value lower than the target metal. This ensures that the sacrificial metal oxidizes first.
This is not just applicable in theory but widely used in practical situations like pipelines, ships, and even in the reinforcing bars within concrete structures.

Electrochemistry

Electrochemistry is the branch of chemistry that studies the movement of electrons, especially in reactions where oxidation and reduction occur simultaneously. This movement is central to how batteries work, how metals corrode, and even how cells in our bodies generate energy.
Electrochemical reactions are divided into two half-reactions: oxidation and reduction. The oxidation reaction is where a substance loses electrons, while the reduction reaction is where a substance gains electrons.
Understanding these reactions' potentials—the standard reduction potential—is crucial. It allows us to predict which substances in a chemical mixture will oxidize or reduce under given conditions. This knowledge forms the foundation for technologies and techniques like cathodic protection, which capitalize on controlled reactions to prevent unwanted corrosion.

Metal oxidation

Metal oxidation is a process where a metal loses electrons, usually as it reacts with oxygen or other non-metallic substances in its environment, leading to corrosion.
This process can be explained through the concept of redox reactions, where oxidation (loss of electrons) and reduction (gain of electrons) occur simultaneously. In metal oxidation, the metal acts as a reducing agent, which means it gets oxidized by another substance, typically oxygen.
The seriousness of corrosion depends on the metal involved and environmental conditions. In industrial applications, the consequences of metal oxidation include weakened infrastructures, higher maintenance costs, and even failures in systems. Thus, understanding metal oxidation helps in selecting materials and protective strategies to minimize corrosion, such as the use of metals with more negative standard reduction potentials for cathodic protection.