For 12th chemistry students

1. INDEX:
i) Introduction
ii) Mechanism of corrosion of Meta
iii) Electrochemical Mechanism (rusting)
iv) Methods of Prevention of Corrosion
v) Economic Effect
vi) Aim of this project
vii) Requirements
viii) Procedure
ix) Observation
x) Conclusion
xi) Bibliography

2. INTRODUCTION
Metal corrosion is the most common form of corrosion. The corrosion occurs at the
surface of the metal in forms of chemical or electrochemical reactions. This
process significantly reduces the strength, plasticity, toughness and other
mechanical properties of the metallic material. However, because of the metal and
its alloys is still the most important pipe and structure materials, the cost of
corrosion grows significantly with the growth of industries. Thus many scientists
focus on the research of corrosion control in order to reduce the cost of replacing
the rusting metal material. Nowadays, there are mainly two corrosion control
methods that are very popular in the world. One is impressed current and another is
sacrificial anode cathode protection system. In this project, we will focus on the
mechanism and application of the sacrificial anode cathode protection system.

3. Mechanism of corrosion of metal
General Principle of Corrosion: Reaction is the fundamental reaction during the
corrosion process, which the electron can flow from certain areas on the metal
surface to other areas through a solution which can conduct electric currents.

4. Basically, both anodic and cathode reactions have to balance each other out,
resulting in a neutral reaction. Both anodic and cathodic reactions occur
simultaneously at the same rates. What’s more, the site of these electrodes may
consist of either two different kinds of metals, or they may
be on different areas of the same piece of metal, resulting a potential difference
between the two electrodes, so that the oxidation reaction of the metal at the anode
and formation of negative ions at the cathode can take place at the same time.
Similar electrical potentials may also be developed between two areas of a
component made of a single metal as result of small differences in composition or
structure or of differences in the conditions to which the metal surface is exposed.
That part of a metal which becomes the corroding area is called the “anode”. that
which acts as the other electrode of the battery is called “cathode” which does not
corrode, but is an important part of the system. In the corrosion systems commonly
involved, with water containing some salts in solution as the electrolyte. Corrosion
may even take place with pure water, provided that oxygen is present. In such
cases oxygen combines with the hydrogen generated at the cathod

5. Rusting: an Electrochemical Mechanism
Rusting may be explained by an electrochemical mechanism. In the presence of
moist air containing dissolved oxygen or carbon dioxide, the commercial iron
behave as if composed of small electrical cells. At anode of cell, iron passes into
solution as ferrous ions. The electron moves towards the cathode and form
hydroxyl ions. Under the influence of dissolved oxygen the ferrous ions and
hydroxyl ions interact to form i.e., hydrated ferric oxide.

6. Methods of Prevention of Corrosion and Rusting
Some of the methods used:-
1) Barrier Protection: In this method, a barrier film is introduced between
Iron surface and atmospheric air. The film is obtained by painting, varnishing etc.
2) Galvanization: The metallic iron is covered by a layer of more reactive metal
such as zinc. The active metal losses electrons in preference of iron. Thus,

7. protecting from rusting and corrosion.

8. AIM OF THIS PROJECT
In this project the aim is to investigate effect of the metals coupling on the rusting
of iron. Metal coupling affects the rusting of iron. If the nail is coupled with a more
electro-positive metal like zinc, magnesium or aluminum rusting is prevented but if
on the other hand, it is coupled with less electro –positive metals like copper, the
rusting is facilitated.

9. REQUIREMENTS;
1) Two Petri dishes
2) Four test-tube
3) Four iron nails
4) Beaker
5) Sand paper
6) Wire gauge
7) Gelatin
8) Copper, Zinc and Magnesium strips
9) Potassium ferricyanide solutions
10) Phenolphthalein

10. PROCEDURE
1) At first we have to clean the surface of iron nails with the help of sand
paper.
2) After that we have to wind zinc strip around one nail, a clean copper
wire around the second and clean magnesium strip around the third nail.
3) Then to put all these three and a fourth nail in Petri dishes so that they
are not in contact with each other.
4) Keep the covered Petri dishes for one day or so

11. 5) The liquids set to a gel on cooling. Two types of patches are observed
around the rusted nail, one is blue and the other pink. Blue patch is due
to the formation of potassium ferro-ferricyanide where pink patch is
due to the formation of hydroxyl ions which turns colorless
phenolphthalein to pink.

12. OBSERVATION;
S.No Metal Pair Colour of the patch Nails rust or not
1 Iron-Zinc
2 Iron- Magnesium
3 Iron- Copper

13. CONCLUSION;
It is clear from the observation that coupling of iron with more electropositive
metals such as zinc and magnesium resists corrosion and rusting of iron. Coupling
of iron with less electropositive metals such as copper increases rusting.

14. BIBLIOGRAPHY;
For our project we have taken help from following sources;
1) Comprehensive (practical Chemistry-XII)
2) Internet- www.wikipedia.com
3) NCERT Chemistry Textbooks
4) http://projects.icbse.com/chemis try