Identifying Redox Reactions

We can use oxidation states to identify redox reactions, even between nonmetals. For example, is the following reaction between carbon and sulfur a redox reaction  

what element is oxidized What element is reduced We can use the oxidation state rules to assign oxidation states to aU elements on both sides of the equation. 

Carbon changes from an oxidation state of 0 to an oxidation state of +4. In terms of our electron bookkeeping scheme (the assigned oxidation state), carbon loses electrons and is oxidized. Sulfur changes from an oxidation state of 0 to an oxidation state of —2. In terms of our electron bookkeeping schane, sulfur gains electrons and is reduced. In terms of oxidation states, oxidation and reduction are defined as follows  

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EXAM PLE 4.17 Using Oxidation States to Identify Oxidation and Reduction 

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To determine whether electrons are transferred in chemical reactions, chemists use a procedure that assigns an oxidation number (also known as an oxidation state) to each atom in each chemical species. In a redox reaction, electron transfer causes some of the atoms to change their oxidation numbers. Thus, we can identify redox reactions by noting changes in oxidation numbers. 

Oxidation numbers are actual or hypothetical charges, assigned using a set of rules. They are used to describe redox reactions with covalent reactants or products. They are also used to identify redox reactions, and to identify oxidizing and reducing agents. In this section, you will see how oxidation numbers were developed from Lewis structures, and then learn the rules to assign oxidation numbers. 

The following Sample Problem illustrates how to use oxidation numbers to identify redox reactions, oxidizing agents, and reducing agents. 

Identify redox reactions by analyzing changes in oxidation numbers for different atoms in the reaction. 

Explain how oxidation numbers are used to identify redox reactions ... 

What is an oxidation number How is it used to identify redox reactions Explain why, except for ionic... 

Notice that oxidation and reduction must occur together. If one substance loses electrons (oxidation), then another substance must gain electrons (reduction). For now, you simply need to be able to identify redox reactions. In Chapter 16 we will examine them more thoroughly. 

In Section 18.2 you will learn more about redox reactions, including how to balance them. For now, you need to be able to identify redox reactions, as well as oxidizing and reducing agents, according to the following gnideUnes. 

EXA M P L E 4.18 Identifying Redox Reactions, Oxidizing Agents, and Reducing Agents... 

Identifying Redox Reactions, Oxidizing Agents, and Reducing Agents Using Oxidation States (4.9) Example 4.17, 4.18 For Practice 4.17, 4.18 For More Practice 4.17 Exercises 95, 96 ... 

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