Chemistry Project on Metal coupling in rusting of Iron

Study of the Effect of Metal Coupling on the Rusting of Iron

Name: Gourav Dhimankar

Class: XII - A (Science)

CBSE Roll No.: 5456340

School: Kendriya Vidyalaya Ballygunge

Academic Year: 2009-10

Certification

It has been certified that Gourav Dhimankar having CBSE Roll No. 5456340, studying in XII-A (Science), during the academic year 2009-10 has completed a project on the Study of the Effect of Metal Coupling on the Rusting of Iron and has given satisfactory account of this in his project report.

Teacher: Shri A.K. Gupta, PGT Chemistry

Declaration

I, Gourav Dhimankar of Class XII A (Science), Kendriya Vidyalaya Ballygunge, declare that the following project on the Study of the Effect of Metal Coupling on the Rusting of Iron has been accomplished under the able guidance of our Chemistry Teacher, Shri A.K. Gupta.

Acknowledgement

I would like to express my gratitude to Shri A.K. Gupta, our chemistry teacher, whose help and encouragement made this project possible.

I would also like to thank Mr. Vaidya, the Lab Assistant for his help during the completion of this project.

Introduction

Metals and alloys undergo rusting and corrosion. The process by which some metals, when exposed to atmospheric conditions i.e., moist air and carbon dioxide, form undesirable compounds on the surface is known as corrosion. The compounds formed are usually oxides. Rusting is also a type of corrosion but the term is restricted to iron or products made from it. Iron is easily prone to rusting, making its surface rough. Chemically, rust is a hydrated ferric oxide.

Electrochemical Mechanism of Rusting

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

Methods of Prevention of Corrosion and Rusting

Some of the methods used to prevent corrosion and rusting are discussed here:

Barrier Protection: In this method, a barrier film is introduced between the iron surface and atmospheric air. The film is obtained by painting, varnishing, etc.
Galvanization: The metallic iron is covered by a layer of a more reactive metal such as zinc. The active metal loses electrons in preference to iron, thus protecting it from rusting and corrosion.

Aim

Aim: To investigate the effect of metal coupling on the rusting of iron. Metal coupling affects the rusting of iron. If the nail is coupled with a more electropositive metal like zinc, magnesium, or aluminium, rusting is prevented. If, on the other hand, it is coupled with a less electropositive metal like copper, the rusting is facilitated.

Requirements

Two Petri dishes
Four test tubes
Four iron nails
Beaker
Sand paper
Wire gauge
Gelatin
Copper, zinc, and magnesium strips
Potassium ferricyanide solution
Phenolphthalein

Procedure

Clean the surface of the iron nails with the help of sand paper.
Wind a zinc strip around one nail, a clean copper wire around the second, and a clean magnesium strip around the third nail. Place all three, along with a fourth plain nail, in Petri dishes so that they are not in contact with each other.
Fill the Petri dishes with hot agar-agar solution in such a way that only the lower half of the nails are covered with the liquid. Cover the Petri dishes for one day or so.
The liquid sets to a gel on cooling. Two types of patches are observed around the rusted nail - one blue and the other pink. The blue patch is due to the formation of potassium ferro-ferricyanide, while the pink patch is due to the formation of hydroxyl ions which turn colourless phenolphthalein to pink.

Observation

S.No.	Metal Pair	Colour of the Patch	Nail Rusts or Not
1	Iron - Zinc
2	Iron - Magnesium
3	Iron - Copper
4	Iron - Nail (plain)

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.

Bibliography

Comprehensive Practical Chemistry - XII
Internet: www.wikipedia.com, www.encyclopedia.com
NCERT Chemistry Textbooks