lectrochemistry: Oxidation and Reduction

Goal: to identify common agents of oxidation or reduction

Working Definitions:

Oxidizing agents cause the oxidation state of other substances to become more positive by accepting their electrons.Oxidizing agents are themselves reduced. Common oxidizing agents are listed in Figure 1.

Reducing agents cause the oxidation state of other substances to become more negative by releasing electrons to them. Reducing agents are themselves oxidized. Common reducing agents are listed in Figure 1.

Click on the buttons to see common oxidizing and reducing agents. Figure 1

Notice that the reducing agents listed in Figure 1 are mostly alkali and alkaline earth metals, Groups 1a and 2a respectively. Why is it easy for these metals to give up their electrons? Notice also that the oxidizing agents are mostly halogens. Why do Groups 7a and 6a nonmetals find it relatively easy to accept electrons? Atoms in both groups are trying to achieve an octet of valence electrons! It is chemically 'easier' for Groups 1a and 2a to lose 1 or 2 electrons than to gain 6 or 7. The exact opposite holds true for Groups 6a and 7a (it is easier for these atoms to gain 1 or 2 electrons than to lose 6 or 7).

Oxidation occurs when the oxidation state of an atom, molecule, or ion becomes more positive.

Example set 1: { Zn Zn²⁺} { Cr⁴⁺ Cr⁶⁺ } { Se^2– Se }

Reduction occurs when the oxidation state of an atom, molecule, or ion becomes more negative.

Example set 2: { Zn²⁺ Zn } { Cr⁶⁺ Cr⁴⁺ } { SeSe^2– }

Based on the previous definitions, identify the oxidizing agents in the following equations by clicking on them. (Clicking the question mark will reset the problem.)

The reaction represented by the third equation may be unfamiliar, but we can easily deduce the oxidizing agent if we work backwards from what we do know. In this case, we should know that Mg is a common reducing agent (from Figure 1.). Therefore, CH₃Br, bromomethane, has to be the oxidizing agent. Nice detective work!

Before moving to the next page, you should know the definition of an oxidizing agent and a reducing agent. You should also know what occurs during an oxidation and a reduction.

Oxidation and Reduction