CONTENT
*AN INTRODUCTION TO WATER
STERILIZATION
*AIM
*MATERIALS AND METHOD
*THEORY
*PREPARATION OF BLEACHING POWDER
*ADVANTAGES OF BLEACHING POWDER
*CALCULATION
*METHODS USED FOR PURIFICATION OF
WATER ON A LARGE SCALE
*HOW BOILING OF WATER KILLS GERMS
*ROLE OF BLEACHINGPOWDER IN
WATERTREATMENT
*CONCLUTION
AN INTRODUCTION TO
WATER STERILIZATION
Water sterilization represents a
critical process aimed at eradicating
pathogenic microorganisms and
contaminants from water sources,
thereby ensuring safety for consumption
and diverse applications.
By employing a range of techniques
including thermal treatments,chemical
disinfection, and sophisticated filtration
methods—water sterilization has
emerged as a fundamental element of
public health initiatives.
The importance of water sterilization
is pronounced, especially in areas
afflicted by waterborne pathogens.
Contaminated water supplies can
precipitate serious health issues and
epidemics, disproportionately impacting
vulnerable demographics.
Among the most prevalent methods
of sterilization is boiling, which utilizes
elevated temperatures to destroy
harmful microorganisms.
While this technique is both
accessible and effective.
Chemical disinfection, which
involves agents like chlorine or iodine,
presents an alternative strategy for
assuring water safety.
Although it proves effective in
eliminating bacteria and viruses, this
method requires meticulous regulation
to mitigate risks associated with
chemical remnants.
Furthermore, advancements in
ultraviolet (UV) light sterilization signify
a noteworthy progression in improving
water safety.
This technique effectively
neutralizes microorganisms without
relying on chemical disinfectants.
Bleaching powder, also known as
calcium oxychloride (Ca(OCl)₂), is a
chemical compound that releases
chlorine gas when dissolved in water.
Chlorine, a powerful disinfectant,
kills bacteria, viruses, and other
pathogens, ensuring the water is safe to
drink.
This project explores the use of
bleaching powder in water purification,
its chemical properties, applications,
and real-life implications for public
health.
AIM
To explore the process of sterilizing
water using bleaching powder
(Ca(OCl)₂) by understanding the
chemical reaction involved, particularly
the release of chlorine when bleaching
powder reacts with water.
This project aims to:
- Demonstrate how chlorine acts
as a disinfectant.
- Calculate the required amount
of bleaching powder to sterilize a
given volume of water.
- Examine its role in destroying
harmful microorganisms like
bacteria and viruses.
- Assess the efficiency and
limitations of bleaching powder as a
water purification agent.
- Highlight its significance in
rural and urban water treatment
practices
- Explores the use of bleaching
powder in water purification
MATERIALS AND
METHOD
*Materials
S. Materials/ Quantity
No Equipment
.
1 Bleaching Powder 0.1 – 0.5
(Calcium oxychloride) grams
2 Distilled or Tap Water 500 ml
3 Beaker (500 ml) 1
4 Glass Stirring Rod 1
5 Filter Paper 1
6 Funnel 1
7 Test Tubes 2
8 Potassium Iodide (KI) Few drops
Solution
9 Starch Solution Few drops
10 Dropper 1
11 Measuring Spoon or 1
Spatula
12 Safety Gloves and Optional
Goggles
*Method
*Step 1: Preparation of the
Disinfecting Solution
Take 0.1 to 0.5 grams of bleaching
powder using a clean, dry spoon. Add this to
a 500 ml beaker containing tap or distilled
water. Stir the mixture thoroughly using a
glass rod to ensure the bleaching powder is
evenly distributed.
*Step 2: Allow Reaction Time
Let the solution sit undisturbed for 15 to
20 minutes. This allows the chlorine
released from the bleaching powder to react
with and kill harmful bacteria, viruses, and
other microorganisms.
*Step 3: Filter the Solution
(Optional)
If the solution contains undissolved
particles, filter it using filter paper and a
funnel to obtain clear water.
*Step 4: Test for the Presence of
Chlorine
Take a small amount of the treated water
in a test tube. Add a few drops of potassium
iodide (KI) solution followed by a few drops
of starch solution. If free chlorine is
present, the solution will turn blue or
violet, confirming the water has been
sterilized.
*Step 5: Safe Usage
Once sterilized, the water can be used
for drinking or cooking. Make sure the
concentration of bleaching powder is low (as
used above);
“excess chlorine can be harmful
to health”
THEORY
Bleaching powder is calcium
chlorohypochlorite.
By passing Cl2 gas on slaked lime
Ca(OH)2 + Cl2 → 2(Ca(OCl)₂) +
H2O
Bleaching powder
i. White powdered substance having little
yellow ting, with smell of chlorine.
ii.With acids (HCl, dil. H2SO4 etc) chlorine
gas is evolved. Total amount of Cl2 gas
evolved is known as available chlorine;
(generally approx 35%)
CaOCl2 + 2HCl → CaCl 2 + H2O + Cl2
Available chlorine is usually determined
by Bunsen method and for this acetic acid
is added to bleaching powder which
liberates all chlorine.
CaOCl2 + 2CH3COOH → Ca(CH3COO)2
+ H2O + Cl2
THEORY
Now, KI solution is added in excess the
available chlorine from bleaching powder
liberates equivalent amount of Iodine from
KI.
2KI + Cl2 → 2KCl + I2
Iodine thus liberated forms brown
colour complex with excess of KI
KI + I2 → KI3 [ KI.. I2]
Iodine bonded with KI is titrated
against hypo (sodium thiosulphate) till
brown colour disappears.
I2+ 2Na2S2O3 → 2NaI +
Na2S4O6
PREPARATION OF
BLEACHING POWDER
****Bleaching Powder is also known
as Calcium Oxychloride (CaOCl₂). It
is a white powder with a strong smell
of chlorine and is widely used as a
disinfectant and bleaching agent.
➤ Preparation – Industrial Process
****Bleaching powder is prepared on
a large scale by the action of chlorine
gas on dry slaked lime (calcium
hydroxide).
****Chemical Reaction:
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
- Ca(OH)₂ is slaked lime
(solid)
- Cl₂ is chlorine gas (dry)
- The reaction takes place in a
special plant called a
Hasenclever plant.
PREPARATION OF
BLEACHING POWDER
➤ Steps in Preparation:
-Slaked lime (Ca(OH)₂) is spread in
large chambers.
-Dry chlorine gas is passed over it.
-The two react to form bleaching
powder and water.
-The bleaching powder formed is
collected, dried, and stored in airtight
containers.
➤ Conditions for Effective Preparation:
- Dry environment to prevent premature
decomposition.
- Low humidity (moisture spoils
bleaching powder).
- Pure slaked lime (impurities reduce
efficiency).
ADVANTAGES OF
BLEACHING POWDER
1. Strong Disinfectant:
Kills bacteria, viruses, fungi, and
algae by oxidizing their cell structure.
2. Low Cost:
Cheap and readily available —
ideal for rural and emergency water
purification.
3. Stable and Easy to Use:
Can be stored in powder form
and used as needed by diluting in water.
4. Versatile:
Also used in textile, paper, and
laundry industries for bleaching.
Unlike UV or boiling, no energy source
is required.
5. Effective in Large Quantities:
Perfect for treating municipal
water or during floods/disasters.
🧮 CALCULATION 🧮
**To calculate the quantity of
bleaching powder required to sterilize a
given volume of water using its
available chlorine content.
**For safe drinking water, the
recommended chlorine dosage is: 2 mg
of available chlorine per liter of water
**Bleaching powder contains a
certain percentage of available chlorine
(usually between 30–35%).
Let’s assume:
Available chlorine = 35.5% (or 35.5
g in 100 g powder)
That is:
1 g of bleaching powder = 0.355 g
of chlorine
Calculation
Q: How much bleaching powder
is needed to sterilize 1000 liters of
water?
Step 1: Find required chlorine
= 2 mg × 1000 L = 2000 mg = 2 g
Step 2: Use proportion
If 1 g of powder gives 0.355 g chlorine,
then:
Required bleaching powder =
2 g / 0.355 g per gram ≈ 5.63 g
To sterilize 1000 liters of
water, you need approximately 5.63 g
of bleaching powder (with 35.5%
available chlorine).
General Formula:
Bleaching Powder Required (g) =
(Chlorine needed in mg) / (Available
chlorine % × 10)
METHODS USED FOR
PURIFICATION OF
WATER ON A LARGE
SCALE
River lakes ponds ,well does not
generally confirms all the requirements
for drinking water .
for reasoning various types of
impurities following methods or
generally used for cleaning process .
REMOVAL OF SUSPENDED
IMPURITIES
It involves
*chlorination
*sedimentation
*filtration.
1. CHLORINATION
The filtered water is then treated
with chlorine gas, which kills germs.
You can see for yourself that alum helps
the suspended particles of water to
settle down quickly.
Take two similar glasses containing
equal volumes of muddy water and label
them A and B. (You can prepare muddy
water by mixing a teaspoonful of mud
METHODS USED FOR
PURIFICATION OF
WATER ON A LARGE
SCALE
from your garden with the water in the
glass.)
Crush a small crystal of alum (which
you can obtain from a store) between
the folds of a paper and add it to A. Stir
the water in the two glasses and allow
them to stand side by side.
Within a short while, you will find
that the mud has settled down with
clear water above it in glass A, but the
water is still not clear in glass B
SEDIMENTATION
Water pumped from the source
(river, lake or dam) is allowed to stand
in large tanks, called settling tanks, for
a few hours. Mud, sand and other
suspended particles settle down. The
addition of a small quantity of potash
alum (K2SO4 .A12(SO4)3 . 24H2O)
helps the suspended particles to settle
down quickly.
The solid that settles at the bottom
of the tank is called sediment. That is
why these tanks are also called
sedimentation tanks.
The water over the sediment layer is
more or less clean.
3.FILTRATION
The water from the sedimentation
tank is filtered through layers of sand
and gravel.
Filtration is also done through
activated charcoal, which affords better-
quality water.
Activated charcoal is a special type
of charcoal made by heating ordinary
charcoal in vacuum.
This charcoal holds the impurities
strongly
ROLE OF BLEACHING
POWDER IN WATER
TREATMENT
Bleaching Powder:
Various surfaces can be disinfected
with the help of bleaching powder.
Bleach is simply combination of
gaseous form of chlorine with an alkali
solution for example Sodium Hydroxide
whilst bleaching powder is combination
of calcium hydroxide with gaseous form
of Chlorine.
*****The advantage of bleaching
powder is that it is in solid form and
thereby enables the control over
concentration. This makes it easier to
apply and control the dosage which is
most prominent factor while
disinfecting.
Bleaching powder also produces
hypochlorite ions and eradicates the
pathogens the same way as discussed in
Chlorine disinfection
*****The disadvantage of adding
bleaching powder to water is that it
adds to the hardness of water as
calcium is present.
Additionally, it goes under
decomposition continuously hence
making it difficult to analyse the
chlorine concentration
HOW BOILING OF
WATER KILLS GERMS
Boil Water Orders and Notices are often
used by health agencies and drinking water
utilities in response to conditions that create
a potential for biological contamination in
drinking water.
Common reasons for a boil water
response include loss of pressure in the
distribution system, loss of disinfection and
other unexpected water quality problems.
Often these result from other events
such as water line breaks, treatment
disruptions, power outages, floods and other
severe weather.
The standard recommendation for
boiling water is a FULL ROLLING BOIL
for ONE MINUTE and COOL BEFORE
USE.
The term rolling boil facilitates
communication and assures that an effective
pasteurization temperature is reached to kill
or inactivate waterborne pathogens.
Some agencies recommend boiling for
longer
periods, but this extra time is not necessary
and can cause unnecessary power demand
and increase safety concerns
HOW BOILING OF
WATER KILLS GERMS
Because some users may be more
susceptible to illness from water borne
pathogens, public health officials need to
react swiftly to address potential water
quality problems
However, public health officials must
also be conscious of unnecessarily alarming
the public, causing undue economic
disruption, and eroding the public
perception of safe tap water.
Whenever possible, alternate methods to
address water quality concerns, such as
isolating problem water and opening
interconnections with neighbouring systems,
should be used to avoid unnecessary boil
water responses.
More specific directions on these steps
and when a boil water response may be
necessary are provided in Department
guidance and regulations.
“A boil water response is NOT
appropriate when chemical
contamination is present. “
This may increase exposure to chemicals
such as nitrates and solvents by
concentration in the boiled water or by
volatilization into the breathing zone.
Boiling water is also NOT appropriate to
address gross levels of contamination (e.g.
raw sewage or high turbidity) when
particulate matter can impair the
effectiveness of boiling.
Under these conditions, alternate water
sources must be used
CONCLUTION
Water sterilization plays a critical
role in safeguarding public health by
removing harmful microorganisms and
impurities from water sources.
Through methods such as boiling,
sedimentation, filtration, and chemical
disinfection—particularly using
bleaching powder—we can achieve safe,
potable water.
Bleaching powder, or calcium
oxychloride, is especially valuable due
to its strong disinfectant properties, low
cost, and ease of use in large-scale
applications.
Its historical and ongoing relevance
in combating waterborne diseases
underscores its importance in both
everyday use and emergency situations.
While highly effective, careful
handling and precise dosing are
necessary to avoid the risks associated
with chemical residues. Altogether, the
integration of traditional practices with
scientific advancements ensures a
sustainable approach to water
CONCLUTION
purification and public health
protection.
