Chemistry Reference
In-Depth Information
Example 1
For the following redox reaction, identify:
A. The oxidation numbers for each substance involved.
B. The substance being oxidized.
C. The oxidizing agent.
D. The substance being reduced.
E. The reducing agent.
2Na + Cl
2
2NaCl
Well, that may seem like a tall order, but it is really quite easy. I will walk
you through a couple examples, and then you will see how easy they can be.
A.
Remember: The oxidation number of an element in its free state is 0,
so both the sodium and chlorine on the reactant side will be assigned
an oxidation number of 0.
2Na
0
+ Cl
2
0
2NaCl
As far as the elements in the compound NaCl, we will recall other
rules for assigning oxidation numbers. Chlorine is a halogen from
column 17 on the periodic table and it is acting as a negative ion in the
compound sodium chloride. Rule #5 tells us that the oxidation number
of a halogen, when it is acting as a negative ion, is -1. Rule #2 tells us
that the oxidation number of an element from group 1, such as sodium,
will be +1 in compounds. These two rules seem to agree with each
other, because sodium and chlorine combine in a 1:1 ratio in this
compound. We can now finish the oxidation numbers for our equation.
2Na
0
+ Cl
2
0
2Na
1+
Cl
1-
B. The substance that is being oxidized is the substance that appears to lose
electrons. Na goes from an oxidation number of 0 to +1, so it appears to
lose one electron. Sodium, Na, is the substance being oxidized.
C. The oxidizing agent is the substance that causes the oxidation or, in
other words, takes the electrons. Chlorine, Cl
2
, is the oxidizing agent.
D. The substance that is reduced is the substance that gains electrons or
appears to gain electrons, as its oxidation number is algebraically de-
creased. That definition describes what happens to chlorine in this re-
action. Chlorine (Cl
2
) is the substance being reduced.
E.
The reducing agent is the substance that causes the reduction to take
place, by giving up the electrons. Sodium (Na) is the reducing agent.
