Corrosion Undesirable Redox Reactions

Corrosion is the (usually) gradual, nearly always undesired, oxidation of metals that are exposed to oxidizing agents in the environment. From Table 18.1, we can see that the reduction of oxygen in the presence of water has an electrode potential of -bO.40 V. 

In the presence of acid, the reduction of oxygen has an even more positive electrode potential of -1-1.23 V. 

The reduction of oxygen, therefore, has a strong tendency to occur and can bring about the oxidation of other substances, especially metals. Notice that the half-reactions for the reduction of most metal ions are listed below the half-reactions for the reduction of 

The oxides of iron, however, are not structurally stable, and they tend to flake away from the underlying metal, exposing it to further corrosion. A significant part of the iron produced each year is used to replace rusted iron. Rusting is a redox reaction in which iron is oxidized according to the following half-reaction  

The overall reaction has a cell potential of -1-1.68 V and is highly spontaneous. 

A Paint can prevent underlying iron from rusting. However, if the paint becomes scratched, the iron will rust at the point of the chip. Question Why  

The Fe(OH)2 formed in the overall reaction then undergoes several additional reactions to form Fe203, the familiar orange substance that we call rust. One of the main problems with Fe203 is that it crumbles off the solid iron below 

Police use a device called a breathalyzer to measure the amount of ethyl alcohol (C2H5OH) in the bloodstream of a person suspected of driving under the influence of alcohol. 

Breathalyzers work because the amount of ethyl alcohol in the breath is proportional to the amount of ethyl alcohol in the bloodstream. One type of breathalyzer employs a fuel cell to measure the amount of alcohol in the breath. The fuel cell 

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SECTION 20.8 Electrochemical principles help us understand corrosion, undesirable redox reactions in which a metal is attacked by some substance in its environment The corrosion of iron into rust is caused by the presence of water and oxygen, and it is accelerated by the presence of electrolytes, such as road salt. The protection of a metal by putting it in contact with another metal that more readily undergoes oxidation is called cathodic protection. Galvanized iron, for example, is coated with a thin layer of zinc because zinc is oxidized more readily than iron, the zinc serves as a sacrificial anode in the redox reaction. 

Oxidation States Electron Bookkeeping 581 16.8 Corrosion Undesirable Redox Reactions 598... 

Corrosion Undesirable Redox Reactions 898 Key Learning Outcomes 903... 

In this section we examine the undesirable redox reactions that lead to corrosion of metals. Corrosion reactions are spontaneous redox reactions in which a metal is attacked by some substance in its environment and converted to an unwanted compound. 

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