The document describes an experiment on the corrosion of different metals and metal alloys in acidic and basic solutions. Key findings include: - Brass and iron corroded most in acid, while brass and zinc corroded most in base. Aluminum corroded least in both. - Coupling metals affected corrosion rates, with iron-aluminum coupling corroding most in acid and brass-aluminum in base. - Corrosion is explained by the electrochemical process and metal reactivity based on their reduction potentials. - Common corrosion protection methods are also outlined.

2.  Acknowledgement
 Certificate
 Introduction
 Resistance to corrosion
 Aim
 Materials Required
 Theory
 Procedure
 Observations
 Conclusions
 Precautions
 Protection from corrosion
 Biblography

3. I am using this opportunity to express my gratitude to
everyone who supported me throughout the course
of this project.
I am thankful for their aspiring guidance, invaluably
constructive criticism and friendly
advice during the project work. I am sincerely grateful
to them for sharing their truthful and
illuminating views on a number of issues related to
the project.
I would like to express my special thanks of gratitude
to my teacher Mr.Najumudeen as well as our
principal Mr.Krishnamoorthy who gave me the golden
opportunity to do this wonderful project on the topic
“Effect of Metal Coupling on Corrosion”, which also
helped me in doing a lot of Research and
I came to know about so many new things I am really
thankful to them.
Secondly I would also like to thank my parents and
friends who helped me a lot in finalizing this project
within the limited time frame.
P. Reshop nanda
Class : XII-A6

4. • Corrosion is the gradual destruction of materials
(usually metals) by chemical reaction with their
environment.
• Corrosion is a serious problem of some metals
like iron, zinc, aluminium and alloys like brass
which are commonly used in day to day life.
• Basically , this means
electrochemical oxidation of metals in reaction
with an oxidant such as oxygen.
• Rusting, the formation of iron oxides, is a well-
known example of electrochemical corrosion.
This type of damage typically produces oxide(s)
or salt(s) of the original metal.
• Corrosion can also occur in materials other than
metals, such as ceramics or polymers, although in
this context, the term degradation is more
common.
• Corrosion degrades the useful properties of
materials and structures including strength,
appearance and permeability to liquids and
gases.

5. EXAMPLES OF
CORROSION

6. • Some metals are more intrinsically resistant to
corrosion than others .
• There are various ways of protecting metals from
corrosion (oxidation) including painting, hot dip
galvanizing, and combinations of these.
• Gold nuggets do not naturally corrode, even on a
geological time scale.
• The materials most resistant to corrosion are
those for which corrosion
is thermodynamically unfavorable. Any corrosion
products of gold or platinum tend to decompose
spontaneously into pure metal, which is why
these elements can be found in metallic form on
Earth and have long been valued. More common
"base" metals can only be protected by more
temporary means.

7. Metals resistance to corrosion:

9. • Beakers-15
• Iron sheets of 2
• Aluminium rods of 2
• Brass rods of 2
• Zinc sheets of 2
• Measuring cylinders
• Chemical Balance
• Weight Box.
• Hydrochloric acid and
• Sodium hydroxide.

11. 1. Mix 9 ml. of conc. HCl with 241 ml. of water to form
250 ml. of solution.
2. Take this solution in seven different beakers.
3. Mark each beaker serially from 1 to 7.
4. Take the weights of three iron sheets, three
aluminium rods, three brass rods and three zinc
sheets.
5. Now keep iron sheets, aluminium rods, zinc sheets
and brass rod in separate beakers
6. Then take iron + brass, iron + aluminium, iron + zinc,
aluminium + zinc and brass + zinc and keep them in
different beakers.
7. Allow the reactions to occur for 24 hours.
8. Note the maximum and minimum temperatures.
9. Now at the end of reaction take out the metals and
keep them in sun for sometime so that they get
dried up quickly
10. Take the weights of each specimen and note the
difference.
11. Similarly repeat 1,2,3,4,5,6,7 and 8 steps in a basic
solution.

12. Sl.
No
Specimen (with acid) Initial weight
(in gm)
Final weight
(in gm)
1 Brass 8 5
2 Iron 8 6
3 Zinc 8 6.50
4 Aluminium 8 7.10
5 Aluminium + Iron 15 12.30
6 Brass + Zinc 15 13.00
7 Iron + Zinc 15 14.10
These experiments are done under
acidic condition

13. Sl.
No
Specimen (with base) Initial weight
(in gm)
Final weight
(in gm)
1 Brass 8 5.80
2 Iron 8 6.20
3 Zinc 8 7.10
4 Aluminium 8 7.60
5 Aluminium + Iron 15 12.90
6 Brass + Zinc 15 13.60
7 Iron + Zinc 15 14.40
These experiments are done under basic
condition

15. • The rate of corrosion observed in acidic medium or
the mass consumed during the corrosion is in the
decreasing order from brass to aluminum.
Brass has the highest corrosion rate while aluminium
has the least corrosion rate.
Brass > Iron > Zinc > Aluminium
• When coupling of these metals was done each couple
showed some difference in their corrosion with
respect to each metal kept alone
Iron + Aluminium couple has the highest rate of
corrosion while iron +Zinc couple has the lowest rate
of corrosion.
Rate of corrosion of each couple is in the order of
Iron + Aluminium > Brass + Zinc> Iron + Zinc

16. • Rate of corrosion in basic medium is in
the decreasing order from Brass to
Aluminium.
The order of rate of corrosion is as
below:
Brass > Zinc >Iron > Aluminium
• When these metals were coupled the
rate of corrosion was in the decreasing
order from
Brass+ Aluminium > Brass + Zinc >
Iron + Aluminium
• Temperature and time of reaction were
constant i.e., temperature was 21° C and
time of reaction was 24 hours.

17. • Corrosion is a serious problem of some metals like
iron, zinc, aluminium and alloys like brass which are
commonly used in day to day life.
• Apart from reducing the life of articles made up of
these metals or alloys the chemical substances formed
out of corrosion have serious public health problems.
• Replacement of machines or their parts and many
other articles in industrial and public dealing lead to
huge expenditure.
• Hence, how to reduce or avoid corrosion of articles
made up of metals or alloys has been a major subject
of study in the field of chemistry and electro-
chemistry.
• The study of the rate of corrosion of different metals
or alloys showed gradual decrease in their masses in
acidic medium. The decrease is in the order of brass,
iron, zinc, aluminium.
• The present experiments are in full agreement with
the well known electro-chemical reaction. Some of the
typical reactions as occur with iron are illustrated.

18. • The reactions at respective
electrodes are:
At cathode: Fe Fe + 2e.
in acid the equilibrium is
HCl H + Cl .
At anode:
The water which is in equilibrium
H O H + OH.
2
2
Here the Fe2+ cation will readily take Cl and form
FeCl . While H of acid will be reacting with
another H+ of water and will form H gas. While
OH. Anion will also react with some of the iron and
will form Fe(OH) which is observed in the form of
rust.
3
3
2

19. • The e.m.f of these metals are in the order of
Al:Zn:Fe .
The values are e.m.f
Al Al3 + 3e- 1.66V
Zn Zn2 + 2e- 0.76V
Fe Fe 2 + 2e- 0.44V
Brass which is an alloy of zinc and copper has the
e.m.f. 0.42V during the forward reaction or
oxidation reaction.
While in backward reaction the e.m.f. value is
0.42.
This is because during oxidation reaction the
e.m.f values of zinc and copper are .0.76 and
+ 0.34, respectively. That is why the value differs.

20. • In acid there are replaceable H ions which react with
metals and H2 gas is evolved. This is because all the
metals are highly electronegative in nature. When
these two come in contact they react very easily and
form stable compounds. Thus the rate of corrosion is
very high. The rate of corrosion in basic medium is
very less as compared to acidic medium.
• This is shown because of following factors:
(i) Ex: sodium hydroxide .
NaOH which is in equilibrium with Na and OH. ions.
NaOH Na + OH
When NaOH comes in contact with water the two ions
immediately dissociate. The hydrates Na+ ions will
take the H+ ion.
The electropositive characters here will be the main
factor in the slow rate of corrosion. Na being more
electropositive than the metal mentioned above, most
of OH ions will be taken by Na when compared to the
other metals
i.e., the rate of corrosion is slow with Na+ Fe2+ ||
OHOH- While H+ + electron = H H + H = H2 gas.
-+
+
+ -
+

21. Plating, painting, and the application of enamel are the
most common anti-corrosion treatments. They work by
providing a barrier of corrosion-resistant material
between the damaging environment and the structural
material.
Cathodic protection (CP) is a technique to control the
corrosion of a metal surface by making that surface the
cathode of an electrochemical cell. Cathodic protection
systems are most commonly used to protect steel, water,
and fuel pipelines and tanks; steel pier piles, ships, and
offshore oil platforms.
Anodic protection impresses anodic current on the
structure to be protected (opposite to the cathodic
protection). It is appropriate for metals that exhibit
passivity (e.g., stainless steel) and suitably small passive
current over a wide range of potentials. It is used in
aggressive environments, e.g., solutions of sulfuric acid.

22. galvanization
Cathodic protection

23. 1. XII class Chemistry NCERT Books
2. iCBSE.com
3.XII class Chemistry Practical Book
4.Photos from Google images.
5.More Information from
Wikipedia..