That location at which reduction occurs is called the
cathode. Furthermore, it is possible for two or more of
the reduction reactions above to occur simultaneously.
If no other oxidation or reduction reactions occur, the total
electrochemical reaction is just the sum of reactions 16.8 and 16.9,
or
Another example is the oxidation or rusting of iron in water, which
contains dissolved oxygen. This process occurs in two steps; in the
first, Fe is oxidized to Fe2�[as Fe(OH)2],
As a consequence of oxidation, the metal ions may either go into the
corroding solution as ions (reaction 16.8), or they may form an
insoluble compound with nonmetallic elements as in reaction 16.12.
ELECTRODE POTENTIALS
| – |
e– |
0.780 V |
e– |
+
|
FIGURE 16.2 An electrochemical cell
|
|
|
| Fe2+ solution, |
|
or Cu2�ions will deposit (electrodeposit) as metallic copper on the
copper electrode, while iron dissolves (corrodes) on the other side of
the cell and goes into solution as Fe2�ions. Thus, the two half-cell
reactions are represented by the relations
Now consider another galvanic couple consisting of the same iron
half-cell connected to a metal zinc electrode that is immersed in a
1M solution of Zn2�ions (Figure 16.3). In this case the zinc is
the anode and corrodes, whereas the Fe now becomes the cathode. The
electrochemical reaction is thus
