Helpful for experiment in chemistry lab

1. Chemistry Project File
Effect of metal coupling on rusting
of iron
Submitted By: Paras Yadav
Class: XII-A
Submitted To: Mr. Amarnath Sinha

2. Index
TOPIC PAGE NO.
 Certificate 1
 Acknowledgement 2
 Introduction 3
 Prevention 5
 Treatment 7
 Coupling Reaction 8
 Experiment 9
 Bibliography 12

3. Certificate
It has been certified that Paras Yadav studying in XII-A,
during the academic year 2017-2018 has completed the project
on the study of the effect of metal coupling on the rusting of
iron and has given satisfactory account of this in her project
report.
Mr. Amarnath Sinha External examiner
(PGT Chemistry)
Signature Signature

4. Acknowledgement
I would like to express my gratitude to Mr. Amarnath Sinha,
our chemistry teacher, whose help and encouragement made
this project possible.
I would also like to thanks to Mr. Nitin, the lab assistant for
his help during the completion of this project.
Paras Yadav
XII- A

5. Introduction
Metals and alloys undergo rusting and corrosion. The process by which some
metals when exposed to atmospheric condition i.e. moist air, 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 it surface rough. Chemically, rust is a hydrated ferric oxide.
Rust is formed by the redox reaction of iron and oxygen in the presence of
water or air moisture. Rust consists of hydrated iron (III) oxides Fe2O3.nH2O
and iron (III) oxide-hydroxide (FeO(OH), Fe(OH)3).
Rust is another name for iron oxide, which occurs when iron or an alloy that
contains iron, like steel, is exposed to oxygen and moisture for a long period
of time. Over time, the oxygen combines with the metal at an atomic level,
forming a new compound called an oxide and weakening the bonds of the
metals itself.
Rusting may be explained by an electrochemical mechanism. In the presence
of moist air containing dissolved oxygen or carbon dioxide, the commercial
iron behaves as if composed of small electrical cells. At anode of cell, iron
passes into solution as ferrous ions.
Fe Fe2+ + 2e-

6. The electrons from the above reaction move towards the cathode and form
hydroxyl ions
H2O + (O) + 2e- 2OH-
Under the influence of dissolved oxygen the ferrous ions and hydroxyl ions
interact to form rust, i.e., hydrated ferric oxide.
2Fe2+ + H2O + (O) 2Fe3+ + 2OH-
2Fe3+ + 6OH- Fe2O3.3H2O or 2Fe(OH)3
(Rust)
If supply of oxygen is limited the corrosion product may be black anhydrous
magnetite, Fe3

7. Prevention
Rust is permeable to air and water, therefore the interior metallic iron
beneath a rust layer continues to corrode. Rust prevention thus requires
coatings that preclude rust formation.
Some of the methods used to prevent corrosion and rusting are discussed here:
Galvanization:
The metallic iron is covered by a layer of more active metal such as zinc. The
active metal loses electrons in preference to iron.
Zn Zn2+ + 2e-
Thus, protecting iron from rusting and corrosion.
Coatings and Paintings:
Rust formation can be controlled with coatings, such as paint, lacquer, or
varnish that isolate the iron from the environment.

8.  Inhibitors:
Corrosion inhibitors, such as gas-phase or violate inhibitors, can be used to
prevent corrosion inside sealed systems. They are not effective when air
circulation disperses them, and brings in fresh oxygen and moisture.
 Humidity control:
Rust can be avoided by controlling the moisture in the use of silica gel
packets to control humidity in equipment shipped by sea.

9. Treatment
Rust removal from small iron or steel objects by electrolysis can be
done in a home workshop using simple materials such as plastic
bucket, tap water, lengths of rebar, washing soda, baling wire, and a
battery charger.
Rust may be treated with commercial products known as rust
converter which contain tannic acid which combines with rust.
Coupling reaction
A coupling reaction in organic chemistry is a general term for a variety
of reactions where two fragments are coupled with an aid of metal

10. catalyst. In one important reaction type a main group organometallic
compound of the type RM(R= organic fragment, M= main group
centre) reacts with an organic halide of the type R’X with formation
of a new carbon-carbon bond in the product R-R’.
 Catalysts involved in metal coupling
reaction:
The most common catalyst is palladium, but an increasing number of
reactions use nickel. Other catalysts include copper, platinum, iron,
cobalt, and amines.

11. Experiment
 Aim:
To study the effect of metal coupling on rusting of iron.
 Requirements:
Two petridishes, four test tubes, four iron nails, beaker, sand paper,
wire gauge. Gelatin, copper, zinc, magnesium strips, potassium
ferricyanide solution, phenolphthalein.
 Procedure:
Clean the surface of iron nails with the help of sand paper. Wash
them with carbon tetrachloride and dry on filter paper.
Wind a clean zinc strip around one nail, a clean copper wire
around the second and clean magnesium strip around the third
nail. Put all these third and a fourth nail in petridishes so that
they are not in contact with each other.
Preparation of agar agar solution. Heat about 3gm of agar agar
in 100ml of water taken in a beaker until solution becomes clear.
Add about 1ml of 0.1M potassium ferri-cyanide solution, 1ml of
phenol-phthalein solution and stir well the contents.

12. Fill the petridishes with hot agar agar solution in such a way
that only lower half of the nails are covered with the liquids.
Keep the covered petridishes undisturbed for one day or so.
The liquid sets to a gel on cooling. Two types of patches are
observed around the rusted nail, one is blue and the other is pink.
Blue patch is due to the reaction between ferrous ions and
potassium ferricyanide, to form potassium Ferro-ferricyanide,
KFe [Fe(CN)6] whereas pink patch is due to the formation of
hydroxyl ions which turns colorless phenolphthalein to pink.
Observations:
S.No. Metal pair Colour of the
patch
Nail rusts or
not
1. Iron-zinc pink No
2. Iron-
magnesium
Pink No
3. Iron-copper blue Yes
4. Iron -nail blue Yes

13.  Conclusion:
It is clear from the observations that coupling of iron with more
electropositive metal such as zinc and magnesium resists corrosion and
rusting of iron. Coupling of iron with less electropositive metal such as
copper increases rusting.

14. Bibliography:
NCERT Chemistry – XII
Comprehensive Practical Chemistry – XII
www.scribd.com
www.google.com
Wikipedia