Chemistry Project

Sterilization
of Water
using
Bleaching
Powder
By Saanvi Gupta
12-B
Contents
1. Certificate
2. Acknowledgement
3. Introduction
• Importance of water
• Purification of water
• Importance of a stable purification technique
4. Theory
• History of Water Purification
• Bleaching Powder
• Use of bleaching powder in sterilisation of water
5. Experiment
• Aim
• Pre-Requisite Knowledge
• Materials Required
• Procedure
6. Result
7. Bibliography
 Certificate
This is to certify that, Saanvi Gupta, a student of class 12-B
has successfully completed the project on the topic
“Sterilization of Water using Bleaching Powder”, under the
guidance of Dr. Seema Sharma (Subject Teacher: Chemistry)
during the session 2024-25.
Acknowledgement
I take this opportunity to express my gratitude towards my
chemistry teacher Dr. Seema Sharma, for her precious
and valuable guidance which played a crucial role in not
only my investigatory project on the topic “Sterilization of
Water using Bleaching Powder”, but also throughout the
session with my studies. I am very grateful to the school
as well, for giving me with the necessary facilities and the
infrastructure with helped me perform the experiment.

Last but not the least I would like to thank my parents and
friends for their support throughout the project.
Introduction
Importance of Water
According to experts, water is ranked second only to oxygen as essential for
life. With more than half of your body weight made of water, you couldn’t
survive for more than a few days without it. On the other hand, you can
survive without food for weeks
Water is used in every cell of your body. Water travels throughout your body
carrying nutrients, oxygen, and wastes to and from your cells and organs.
Water keeps your body cool as part of your body’s temperature regulating
system. Water cushions your joints, and protects your tissues and organs
from shock and damage. Water acts as a lubricant for your joints, your mouth
and digestive system in saliva, and in your nose, throat, eyes, and stomach as
part of mucus. Water aids in digestion and absorption of food, as well as in
the removal of wastes from your body.

With the increasing world population, the demand for drinking water has also
increased dramatically and therefore it is very essential to identify resources
of water from which we can use water for drinking purposes. Many available
resources of water do not have it in drinkable form. Either the water contains
excess of calcium or magnesium salts or any other organic impurity or it
simply contains foreign particles which make it unfit and unsafe for drinking.

Purification of Water
There are many methods for the purification of water. Some of them are:

1. Boiling
2. Filtration
3. Bleaching powder treatment
4. SODIS (Solar Water Disinfection)
Boiling is perhaps the most commonly used water purification technique in use
today. While in normal households it is an efficient technique; it cannot be
used for industrial and large scale purposes. It is because in normal
households, the water to be purified is very small in quantity and hence the
water loss due to evaporation is almost negligible. But in industrial or large
scale purification of water the water loss due to evaporation will be quite high
and the amount of purified water obtained will be very less.

Filtration is also used for removing foreign particles from water. One major
drawback of this purification process is that it cannot be used for removing
foreign chemicals and impurities that are miscible with water.

SODIS or Solar Water Disinfection is recommended by the United Nations for

disinfection of water using soft drink bottles, sunlight, and a black surface--
at least in hot nations with regularly intense sunlight.

Water-filled transparent bottles placed in a horizontal position atop a flat

surface in strong sunlight for around five hours will kill microbes in the water.
The process is made even more safe and effective if the bottom half of the
bottle or the surface it's lying on is blackened, and/or the flat surface is made
of plastic or metal. It's the combination of heat and ultraviolet light which kills
the organisms. The major drawback of this purification technique is that it
cannot be used in countries with cold weather. Also, the time consumed for
purification process is more and it also needs a ‘blackened’ surface, much like
solar cookers.

Importance of a stable
purification technique
We need a purification technique which can be used anytime and anywhere,
does not require the use of any third party content and which is also
economically feasible on both normal scale and large scale.
Hence we look at the method of purification of water using the technique of
treatment by bleaching powder commonly known as chlorination.
Theory
History of Water Purification
In 1854 it was discovered that a cholera epidemic spread through water. The
outbreak seemed less severe in areas where sand filters were installed. British
scientist John Snow found that the direct cause of the outbreak was water
pump contamination by sewage water. He applied chlorine to purify the
water, and this paved the way for water disinfection. Since the water in the
pump had tasted and smelled normal, the conclusion was finally drawn that
good taste and smell alone do not guarantee safe drinking water. This
discovery led to governments starting to install municipal water filters (sand
filters and chlorination), and hence the first government regulation of public
water.

In the 1890s America started building large sand filters to protect public
health. These turned out to be a success. Instead of slow sand filtration, rapid
sand filtration was now applied. Filter capacity was improved by cleaning it
with powerful jet steam. Subsequently, Dr. Fuller found that rapid sand
filtration worked much better when it was preceded by coagulation and
sedimentation techniques. Meanwhile, such waterborne illnesses as cholera
and typhoid became less and less common as water chlorination won terrain
throughout the world.

But the victory obtained by the invention of chlorination did not last long.
After some time the negative effects of this element were discovered.
Chlorine vaporizes much faster than water, and it was linked to the
aggravation and cause of respiratory disease. Water experts started looking
for alternative water disinfectants. In 1902 calcium hypo chlorite and ferric
chloride were mixed in a drinking water supply in Belgium, resulting in both
coagulation and disinfection.
The treatment and distribution of water for safe use is one of the greatest
achievements of the twentieth century. Before cities began routinely treating
drinking water with chlorine (starting with Chicago and Jersey City in US in
1908), cholera, typhoid fever, dysentery and hepatitis A killed thousands of
U.S. residents annually. Drinking water chlorination and filtration have helped
to virtually eliminate these diseases in the U.S. and other developed countries.
Meeting the goal of clean, safe drinking water requires a multi-barrier
approach that includes: protecting source water from contamination,
appropriately treating raw water, and ensuring safe distribution of treated
water to consumers’ taps. During the treatment process, chlorine is added to
drinking water as elemental chlorine (chlorine gas), sodium hypochlorite
solution or dry calcium hypochlorite. When applied to water, each of these
forms “free chlorine,” which destroys pathogenic (disease-causing)organisms.
Almost all systems that disinfect their water use some type of chlorine-based
process, either alone or in combination with other disinfectants.

In addition to controlling disease-causing organisms, chlorination offers a

number of benefits including:
• Reduces many disagreeable tastes and odors
• Eliminates slime bacteria, molds and algae that commonly grow in water
supply reservoirs, on the walls of water mains and in storage tanks
• Removes chemical compounds that have unpleasant tastes and hinder
disinfection
• Helps remove iron and manganese from raw water.

As importantly, only chlorine-based chemicals provide “residual disinfectant”

levels that prevent microbial re-growth and help protect treated water
throughout the distribution system.

For more than a century, the safety of drinking water supplies has been
greatly improved by the addition of bleaching powder. Disinfecting our
drinking water ensures it is free of the microorganisms that can cause serious
and life-threatening diseases, such as cholera and typhoid fever. To this day,
bleaching powder remains the most commonly used drinking water
disinfectant, and the disinfectant for which we have the most scientific
information.
Bleaching powder is added as part of the drinking water treatment process.
However, bleaching powder also reacts with the organic matter, naturally
present in water, such as decaying leaves. This chemical reaction forms a
group of chemicals known as disinfection by-products. Current scientific
data shows that the benefits of bleaching our drinking water (less disease)
are much greater than any health risks from THMs and other by-products.
Although other disinfectants are available, bleaching powder remains the
choice of water treatment experts. When used with modern water filtration
methods, chlorine is effective against virtually all microorganisms. Bleaching
powder is easy to apply and small amounts of the chemical remain in the
water as it travels in the distribution system from the treatment plant to
the consumer’s tap, this level of effectiveness ensures that microorganisms
cannot recontaminate the water after it leaves the treatment.

Bleaching Powder
Bleaching powder or Calcium hypochlorite is a chemical compound with
formula Ca(ClO)2. It is widely used for water treatment and as a bleaching
agent. This chemical is considered to be relatively stable and has greater
available chlorine than sodium hypochlorite (liquid bleach). It is prepared by
either calcium process or sodium process.

Calcium Process

2 Ca(OH)2 + 2 Cl2 → Ca(ClO)2 + CaCl2 + 2 H2O

Sodium Process

2 Ca(OH)2 + 3 Cl2 + 2 NaOH → Ca(ClO)2 + CaCl2 + 2 H2O + 2 NaCl

Use of bleaching powder in
sterilisation of water
The combination of following processes is used for municipal drinking water
treatment worldwide:
1. Pre-chlorination - for algae control and arresting any biological growth
2. Aeration - along with pre-chlorination for removal of dissolved iron and
manganese
3. Coagulation - for flocculation
4. Coagulant aids also known as polyelectrolyte’s - to improve coagulation
and for thicker floc formation
5. Sedimentation - for solids separation, that is, removal of suspended solids
trapped in the floc
6. Filtration - for removal of carried over floc
7. Disinfection - for killing bacteria

Out of these processes, the role of bleaching powder is only in the last step
i.e. for disinfection of water.

This chemical can be used for sterilizing water by Using 5 drops of bleach per
each half gallon of water to be purified, and allowing it to sit undisturbed for
half an hour to make it safe for drinking. Letting it sit several hours more will
help reduce the chlorine taste, as the chlorine will slowly evaporate out. A
different reference advises when using household bleach for purification;
add a single drop of bleach per quart of water which is visibly clear, or three
drops per quart of water where the water is NOT visibly clear. Then allow the
water to sit undisturbed for half an hour.
Experiment
Aim
To determine the dosage of bleaching powder required for sterilization or
disinfection of different samples of water

Pre-Requisite Knowledge
1. A known mass of the given sample of bleaching powder is dissolved in
water to prepare a solution of known concentration. This solution contains
dissolved chlorine, liberated by the action of bleaching powder with water.

CaOCl2 + H20 → Ca(OH) 2 + Cl2

2. The amount of Chlorine present in the above solution is determined by

treating a known volume of the above solution with excess of 10% potassium
iodide solution, when equivalent amount of Iodine is liberated. The Iodine,
thus liberated is then estimated by titrating it against a standard solution of
Sodium thiosulphate, using starch solution as indicator.

Cl2 + 2KI → 2KCl + I2

I2 + 2Na2S2O3 → Na2S4O6 + 2NaI

3. A known volume of one of the given samples of water is treated with a

known volume of bleaching powder solution. The amount of residual chlorine
is determined by adding excess potassium iodide solution and then titrating
against standard sodium thiosulphate solution.

4. From the readings in 2 and 3, the amount of chlorine and hence bleaching
powder required for the disinfection of a given volume of the given sample of
water can be calculated.
Materials Required
Burette, titration flask, 100ml graduated cylinder, 250ml measuring
flask, weight box, glazed tile, glass wool, bleaching Powder, Glass wool, 0.1 N
Na2S2O3 solution, 10% KI solution, different samples of water, starch solution

Procedure
1.Weigh accurately 2.5g of the given sample of bleaching powder and
transfer it to a 250ml conical flask. Add about 100ml of distilled water.
Stopper the flask and shake it vigorously. The suspension thus obtained is
filtered through glass wool and the filtrate is diluted with water (in a
measuring flask) to make the volume 250ml. The solution obtained is 1%
bleaching powder solution.

2. Take 20ml of bleaching powder solution in a stoppered conical flask and

add it to 20ml of 10% KI solution. Stopper the flask and shake it vigorously.
Titrate this solution against 0.1N Na2S2O3 solution taken in the burette. When
the solution in the conical flask becomes light yellow in color, add about 2ml
starch solution. The solution now becomes blue in color. Continue titrating till
the blue color just disappears. Repeat the titration to get a set of three
concordant readings.

3. Take 100ml of the water sample in a 250ml stoppered conical flask and
add it to 10ml of bleaching powder solution. Then add 20ml of KI solution and
stopper the flask. Shake vigorously and titrate against 0.1N Na2S2O3 solution
using starch solution as indicator as described in step 2.

4. Repeat the step 3 with other samples of water and record the
observations.
Result
Amount of the given sample of bleaching powder required to disinfect one
litre of water

Sample I = ..1.5.....1.......g

Sample II = ..1..4.....7......g
15. 6
Sample III = ..............g
Bibliography
https://www.ctahr.hawaii.edu/new/Newsletters/ImportanceWater.pdf
http://en.wikipedia.org/wiki/Bleach
http://en.wikipedia.org/wiki/Water_treatment
http://en.wikipedia.org/wiki/Bleaching_powder

Drinking Water Treatment: Continuous Chlorination

http://www.ianrpubs.unl.edu/epublic/pages/publicationD.jsppublicationId

Chlorination of Drinking Water

http://www.water-research.net/watertreatment/chlorination.htm

Chlorination Of Drinking Water (2)

www.edstrom.com/doclib/mi4174.pdf

The Medical front-Water Supply

http://www.vlib.us/medical/sancamp/water.htm

How to live on Very, Very Little-Clean drinking water: How to develop low
cost sources of drinking water just about anywhere
http://www.jmooneyham.com/watp.html

Drinking Water Standards

www.epa.gov/safewater/mcl.html

Understanding the New Consumer Confidence Report

www.awwa.org/Advocacy/bluethumb98/consumer.cfm