EXPERIMENT 7

SOME ASPECTS OF CORROSION

III. Results and Discussion

A straight and a bended nail were placed side by side at the bottom of the beaker. The same
procedure was done in a nail with a copper wire and a nail with mossy zinc. The two beakers were
left for two days and observed changes were tabulated in Table 1.

SET UP OBSERVATIONS
Straight nail The head region is blue green
in color; the tail region is pink
in color
Bent nail The nail is coated by a blue
green color.
Nail with Cu The nail is blue green all
throughout the body region
Nail with Zn The head region is pink in color
Table 1. Color changes in different nails
Corrosion of metal is an oxidation-reduction reaction in which a metal is oxidized naturally
to its ions, resulting in partial or complete destruction of the metal (Brown et. al, 2009). Since it is
a redox reaction, the site where oxidation happens is called the anode and the site where reduction
process happens is called cathode.
In the straight nail, the head region becomes blue green in color. This is because the nail is
undergoing rusting or corrosion. The bended nail also undergoes corrosion as the blue green color
indicates it. The blue green color shows the reduction of Fe
2+
metal, and the area to which it occurs
is the anode. Since the nail is composed of Fe
2+
, it easily corrodes because the nail does not have any
coating at the same time rusting agents (water and oxygen) are present in the gelatin solution.
Looking at the nail with copper wire, the nail is coated by a blue green color which implies
that the nail is rusting a lot. This is due to the fact that copper is not a good metal to use as a coating
to protect iron from rusting because copper has less oxidizable properties than iron. In nail with
zinc, the head region turns into pink color and no blue color formation is observed. The pink
coloration observed in the nail means that the nail is not undergoing corrosion, and the area where
this color is observed is the cathode. Since zinc is more oxidizable than iron, and the fact that
incorporating a more oxidizable metal to another metal will prevent corrosion, the nail turns into
pink color (Brown et. al, 2009).
Since we used a galvanized iron, which iron is coated by zinc, Principle of Electrochemistry
is observed. Protecting a metal from corrosion by making it the cathode in an electrochemical cell is
called as cathodic protection. The metal that is oxidized while protecting the cathode is called the
sacrificial anode (Brown,2009.)

Answers in the manual are stated below.
a.) What do the blue ends in the straight nail represent?
The blue ends represent cathode to which reduction of iron metal happens.

b.) What does the pink coloration in the gelatin solution indicate?
The pink coloration represents the anode in which oxidation happens.

c.) Compare the results of the nails in beaker A to those in beaker B.
The results yielded in beaker A implies that without surface coating, metals such as iron
undergo corrosion. Since beaker B has nails with surface coating, they do not undergo
rusting; hence, they represent the metals with surface coating that do not undergo
corrosion.

d.) How does the copper wire affect the corrosion of the iron nail?
By looking at the activity series of metals, copper is less oxidizable than iron thus when it is
used as a surface coating to protect iron metal, it enhances the rate of corrosion. We have to
bear in mind that we have to incorporate a more oxidizable metal combination to protect a
certain metal from corrosion.

b.) Explain the effect of the zinc metal on the corrosion of the iron nail.
Since zinc is more active than iron as far as to potential oxidation is concern, it oxidizes first
than iron. And since it has more negative enthalpy reduction value than iron, iron is easier
to reduce than zinc. Thus it protects the iron against corrosion. Therefore zinc serves as
sacrificial anode or sacrificial coating at the same time it serves as cathodic protection to
iron metal.

IV. CONCLUSION

Corrosion is an oxidation-reduction property in which the metal is oxidized naturally into
ions, resulting in partial or complete destruction of metal (Brown et. Al, 2009). This experiment
sought to determine the corrosion of iron in gelatin solution. The group had been able to witness
the corrosion of metal iron when surface coating is absent (in beaker A) and the prevention of its
corrosion using surface coating (in beaker B). Also, the group had applied the principles behind
protection of metals and had been able to see the reasons behind using different metals to coat
certain metals from rusting.

This experiment also gives us the idea on how corrosion is electrochemical in nature. By
knowing the Principle of Electrochemistry, students had been able to know the distinction
between the cathodic protection and sacrificial anode. Cathodic protection is protecting the metal
by making it oxidized while sacrificial anode is the metal being oxidized while protecting the
cathode (Brown et. Al, 2009).

After doing the experiment, students were able to understand how corrosion works and
appreciate its importance not only in the field of Chemistry but also in other field of sciences.


V. REFERENCES

Brown, T.L., H.E. Lemay and B.E. Bursten. 2009. Chemistry: The Central Science. Murphy, C.J. Pearson
Education, Inc., Philippines.