Textbook Question
(b) Can the “fuel” of a fuel cell be a solid?
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Ch.20 - Electrochemistry
Chapter 20, Problem 85
(a) Magnesium metal is used as a sacrificial anode to protect underground pipes from corrosion. Why is the magnesium referred to as a “sacrificial anode”? (b) Looking in Appendix E, suggest what metal the underground pipes could be made from in order for magnesium to be successful as a sacrificial anode.
Verified step by step guidance1
Step 1: Understand the concept of a sacrificial anode. A sacrificial anode is a metal that is more reactive (more easily oxidized) than the metal it is protecting. It corrodes instead of the protected metal, hence the term 'sacrificial'.
Step 2: Identify the role of magnesium in this context. Magnesium is used as a sacrificial anode because it has a higher tendency to oxidize compared to many other metals, meaning it will corrode first, protecting the other metal from corrosion.
Step 3: Refer to Appendix E or a standard electrode potential table to find the standard reduction potentials of various metals. The metal with a more positive standard reduction potential than magnesium will be protected by magnesium.
Step 4: Compare the standard reduction potential of magnesium with other metals. Magnesium has a standard reduction potential of -2.37 V. Look for metals with a more positive standard reduction potential.
Step 5: Suggest a suitable metal for the underground pipes. Based on the comparison, choose a metal like iron (Fe), which has a standard reduction potential of -0.44 V, making it suitable to be protected by magnesium as a sacrificial anode.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Sacrificial Anode
A sacrificial anode is a metal that is intentionally corroded to protect another metal from corrosion. In electrochemical terms, it is more reactive than the metal it protects, thus it oxidizes preferentially. This process is commonly used in cathodic protection systems, where the sacrificial anode, like magnesium, corrodes instead of the underground pipes, extending their lifespan.
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Electrochemical Series
The electrochemical series is a list of metals arranged by their standard electrode potentials. It indicates the tendency of a metal to be oxidized or reduced in electrochemical reactions. Metals higher in the series, such as magnesium, are more reactive and can serve as sacrificial anodes, while metals lower in the series are less reactive and can be protected from corrosion.
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Corrosion
Corrosion is the gradual destruction of materials, usually metals, due to chemical reactions with their environment. It often involves oxidation, where metals lose electrons and form oxides or other compounds. Understanding corrosion is essential for selecting appropriate materials and protective measures, such as using sacrificial anodes, to prevent damage to structures like underground pipes.
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Related Practice
Textbook Question
Iron corrodes to produce rust, Fe2O3, but other corrosion products that can form are Fe(O)(OH), iron oxyhydroxide, and magnetite, Fe3O4. (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? (O)(OH), iron oxyhydroxide, and magnetite, Fe3O4. (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.
Textbook Question
Copper corrodes to cuprous oxide, Cu2O, or cupric oxide, CuO, depending on environmental conditions. (a) What is the oxidation state of copper in cuprous oxide?