Because the oxidation states of the elements in the first reaction don’t
change, this reaction is not a redox process. You should recognize this as a
precipitation reaction, as described in Chapter 8. The second reaction does
exhibit a change in oxidation states and should be viewed as a redox reaction. In
this reaction the sodium is being oxidized and the chlorine is being reduced. The
chlorine could not be reduced (i.e., gain electrons) if the sodium wasn’t being
oxidized (i.e., losing electrons.) In one regard, the sodium is acting as a facilitator
for the reduction of the chlorine. As such, it is referred to as a reducing agent.
Likewise, the sodium would not lose its electron if it had nowhere to go, so the
chlorine is referred to as the oxidizing agent in this reaction. Oxidizing agents,
then, contain elements that are capable of being reduced by other substances
(reducing agents) that contain elements that are capable of being oxidized.
Sometimes the terms oxidizer and reducer are used as labels on the bottles of
substances with the tendency to act as oxidizing and reducing agents, respectively.
Sample Problem 1
Identify the elements that are being oxidized and reduced in the following
reaction. Also, name the oxidizing and reducing agents.
2H 2 O(ℓ) + 2MnO 4 −(aq) + I−(aq) → 2MnO 2 (aq) + IO 3 −(aq) + 2OH−(aq)The oxidation states of the hydrogen and oxygen are not changing in the
reaction. The oxidation states of the manganese and the iodine are changing, as
shown below.
Since the manganese is changing from an oxidation state of +7 to that of +4,
the manganese is being reduced. The iodine is being oxidized from a value of −1
to a value of +5. Manganese is gaining electron responsibility while iodine is
losing it. In that light, then, the permanganate ion (MnO 4 −), which contains the
manganese, is facilitating the process in which iodine is being oxidized and so is
referred to as the oxidizing agent. A typical source of the permanganate ion in
chemical reactions like this one is from the compound potassium permanganate,
KMnO 4 , whose bottle is generally labeled with the term “oxidizer.” Along a line
of similar thinking, the iodide ion, I−, can be called the reducing agent in this
reaction.