CERTIFICATE

This is to certify that the project has been satisfactorily performed by Master

RUSHIL AGGARWAL studying in NAVY CHILDREN SCHOOL of class XII-A under the

guidance of Mr. Anit Rana during the academic year 2015-2016.

Signature of Head Of Department Signature of External Examiner

School Stamp

Acknowledgement

I would like to express my sincere gratitude to my

Chemistry mentors Mr. Anit Rana and Mrs. Vishu for

their vital support guidance and encouragement without

which this project would not have come forth from my

side.

I would like to express my heartily gratitude to the lab

assistants Mrs. Sanchita , Mr. Pandurang and Mr. Vivek

for their support during the making of this project .

I would like to thank my parents and friends who have

helped me with their valuable suggestions and guidance

has been helpful in various phases of the completion of

the project.

I would like to acknowledge the Almighty God who made

all the things possible.

INTRODUCTION

ELECTROCHEMICAL MECHANISM (Rusting)

METHODS OF PREVENTION OF CORROSION

AIM

MATERIALS REQUIRED

PROCEDURE

OBSERVATION

ASSOCIATED REACTIONS

CONCLUSION

BIBLIOGRAPHY

Index

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 its surface rough. Chemically, rust is a hydrated ferric oxide .

Titanic‘s bow exhibiting microbial corrosion damage in the form of ‘rusticles’

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 rust,

i.e., hydrated ferric oxide.

Methods of Prevention of

Corrosion and Rusting

Some of the methods used to prevent corrosion and rusting are –

Barrier Protection –

In the method , a barrier film is introduced between iron surface and

atmospheric air. The film is obtained by painting, varnishing etc.

Sacrificial Protection –

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,

protecting from rusting and corrosion.

Electrical Protection –

The metallic iron is connected with more active metals like magnesium or zinc. The active metal has lower reduction potential than iron and will lose electron in preference to iron, This method is used for protecting iron articles which are in contact with water.

Anti-Rust Solution –

To retard the corrosion of iron, certain anti-rust solutions are used . example – alkaline phosphate and alkaline chromates.

Aim

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.

Materials Required

1)Two Petri dishes

2) Four iron nails

3) Beaker

4) Sand paper

5) Wire gauge

6) Gelatin

7) Copper, zinc & magnesium strips

8) Potassium ferricyanide solution

9) Phenolphthalein

10) Bunsen Burner

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 & clean magnesium strip around the third nail.

Then to put all these three and a fourth nail in Petri dishes so that they

are not in contact with each other.

3) Then to fill the Petri dishes with hot agar-agar solution in such a way

that only lower half of the nails are covered with the liquids .Covered

Petri dishes for one day or so.

4) 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 𝑲𝑭𝒆[𝑭𝒆(𝑪𝑵)𝟔] where

pink patch is due to the formation of hydroxyl ions which turns colourless

phenolphthalein to pink.

Observation

S.No. Metal Pair Colour of the patch

Nails Rust

1

Iron-Zinc

Pink

No

2

Iron-Magnesium

Pink

No

3

Iron-Copper

Blue

Yes

4

Iron-Nail

Blue

Yes

Associated reactions

The rusting of iron is an electrochemical process that begins with the transfer of electrons from iron to oxygen. The iron is the reducing agent (gives up electrons) while the oxygen is the oxidising agent (gains electrons). The rate of corrosion is affected by water and accelerated by electrolytes, as illustrated by the effects of road salt on the corrosion of automobiles.

The key reaction is the reduction of oxygen

𝑶𝟐 + 𝟒𝒆− + 𝟐𝑯𝟐 𝑶⟶ 𝟒𝑶𝑯−

Because it forms hydroxide ions, this process is strongly affected by the presence of acid. Indeed, the corrosion of most metals by oxygen is accelerated at low pH.

Providing the electrons for the above reaction is the oxidation of iron that may be described as follows:

𝑭𝒆 ⟶ 𝑭𝒆𝟐+ + 𝟐𝒆−

The following redox reaction also occurs in the presence of water and is crucial to the formation of rust:

𝟒𝑭𝒆𝟐+ + 𝑶𝟐 ⟶ 𝟒𝑭𝒆𝟑+ + 𝟐𝑶𝟐 −

In addition, the following multistep acid-base reactions affect the course of rust formation:

𝑭𝒆𝟐+ + 𝟐𝑯𝟐𝑶⟶ 𝑭𝒆(𝑶𝑯)𝟐 + 𝟐𝑯+

𝑭𝒆𝟑+ + 𝟑𝑯𝟐𝑶⟶ 𝑭𝒆(𝑶𝑯)𝟑 + 𝟑𝑯+

as do the following dehydration equilibria:

𝑭𝒆(𝑶𝑯)𝟐 ⟶ 𝑭𝒆𝑶 +𝑯𝟐𝑶

𝑭𝒆(𝑶𝑯)𝟑 ⟶ 𝑭𝒆𝑶(𝑶𝑯) + 𝑯𝟐𝑶

𝟐𝑭𝒆𝑶(𝑶𝑯) ⟶ 𝑭𝒆𝟐𝑶𝟑 + 𝑯𝟐𝑶

From the above equations, it is also seen that the corrosion products are dictated by the availability of water and oxygen. With limited dissolved oxygen, iron(II)-containing materials are favoured, including FeO and black lodestone or magnetite(𝑭𝒆𝟑𝑶𝟒). High oxygen concentrations favour ferric materials with the nominal formulae 𝑭𝒆(𝑶𝑯)𝟑 − 𝒙𝑶𝒙/𝟐.

The nature of rust changes with time, reflecting the slow rates of the reactions of solids.

Furthermore, these complex processes are affected by the presence of

other ions, such as 𝑪𝒂𝟐+, both of which serve as an electrolyte, and thus accelerate rust formation, or combine with the hydroxides and oxides of iron to precipitate a variety of Ca-Fe-O-OH species.

Onset of rusting can also be detected in laboratory with the use

of ferroxyl indicator solution. The solution detects both 𝑭𝒆𝟐+ ions and hydroxyl ions. Formation of Fe2+ ions and hydroxyl ions are indicated by blue and pink patches respectively.

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

1. www.en.wikipedia.org/wiki/Rust

2. www.class12guide.wordpress.com

3. www.academia.edu/Metal_Coupling

4. NCERT Chemistry Textbook for XII

5. Comprehensive (Practical Chemistry – XII)