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Chapter 20: Problem 86

An iron object is plated with a coating of cobalt to protect against corrosion. Does the cobalt protect iron by cathodic protection?

Short Answer

Expert verified
Cobalt does not provide cathodic protection to the iron object. This is because the standard reduction potential for iron (\(E^0 = -0.44 V\)) is more negative than that of cobalt (\(E^0 = -0.28 V\)), meaning that iron is more easily oxidized. Hence, iron would act as a sacrificial anode for the cobalt, which is not the intended purpose.

Step by step solution

01

Understanding Cathodic Protection

Cathodic protection is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. This is achieved by placing a more easily oxidized metal (having a more negative standard reduction potential) in contact with the metal we want to protect, forming a galvanic cell. The more easily oxidized metal (called the sacrificial anode) will be oxidized, and the protected metal will be reduced, preventing its corrosion.
02

Checking Standard Reduction Potentials

We need to compare the standard reduction potentials of iron and cobalt to determine if cobalt can act as a sacrificial anode for iron. The standard reduction potential for iron (Fe): \(Fe^{2+}(aq) + 2e^- \rightarrow Fe(s)\) \(E^0 = -0.44 V\) The standard reduction potential for cobalt (Co): \(Co^{2+}(aq) + 2e^- \rightarrow Co(s)\) \(E^0 = -0.28 V\)
03

Comparing Standard Reduction Potentials

Now that we have the standard reduction potentials for both iron and cobalt, we can compare them: Iron: \(E^0 = -0.44 V\) Cobalt: \(E^0 = -0.28 V\) Since the standard reduction potential for iron is more negative than that of cobalt, iron is more easily oxidized.
04

Determining Cathodic Protection

As iron has a more negative standard reduction potential, it is more likely to be oxidized than cobalt. Therefore, cobalt cannot provide cathodic protection to the iron object, as it is not more easily oxidized. Instead, the iron would act as a sacrificial anode for the cobalt, which is not the desired outcome.

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Most popular questions from this chapter

You may have heard that "antioxidants" are good for your health. Is an "antioxidant" an oxidizing agent or a reducing agent? [Sections 20.1 and 20.2\(]\)

(a) Based on standard reduction potentials, would you expect copper metal to oxidize under standard conditions in the presence of oxygen and hydrogen ions? (b) When the Statue of Liberty was refurbished, Teflon spacers were placed between the iron skeleton and the copper metal on the surface of the statue. What role do these spacers play?

(a) What is an electrolytic cell? (b) The negative terminal of a voltage source is connected to an electrode of an electrolytic cell. Is the electrode the anode or the cathode of the cell? Explain. (c) The electrolysis of water is often done with a small amount of sulfuric acid added to the water. What is the role of the sulfuric acid? (d) Why are active metals such as Al obtained by electrolysis using molten salts rather than aqueous solutions?

From each of the following pairs of substances, use data in Appendix E to choose the one that is the stronger oxidizing agent: $$ \begin{array}{l}{\text { (a) } \mathrm{Cl}_{2}(g) \text { or } \mathrm{Br}_{2}(l)} \\ {\text { (b) } \mathrm{Zn}^{2+}(a q) \text { or } \mathrm{Cd}^{2+}(a q)} \\ {\text { (c) } \mathrm{Cl}^{-}(a q) \text { or } \mathrm{ClO}_{3}(a q)} \\ {\text { (d) } \mathrm{H}_{2} \mathrm{O}_{2}(a q) \text { or } \mathrm{O}_{3}(\mathrm{g})}\end{array} $$

Iron corrodes to produce rust, \(\mathrm{Fe}_{2} \mathrm{O}_{3},\) but other corrosion products that can form are \(\mathrm{Fe}(\mathrm{O})(\mathrm{OH}),\) iron oxyhydroxide, and magnetite, \(\mathrm{Fe}_{3} \mathrm{O}_{4}\) . (a) What is the oxidation number of Fe in iron oxyhydroxide, assuming oxygen's oxidation number is \(-2 ?\) (b) The oxidation number for Fe in magnetite was controversial for a long time. If we assume that oxygen's oxidation number is \(-2,\) and Fe has a unique oxidation number, what is the oxidation number for Fe in magnetite? (c) It turns out that there are two different kinds of Fe in magnetite that have different oxidation numbers. Suggest what these oxidation numbers are and what their relative stoichiometry must be, assuming oxygen's oxidation number is - 2 .
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