+
semester
www.semesterplus.com
UNIT- I
WATER
TECHNOLOGY
1.1
Introduction
Molecular formula of water: H2O
Water is one of the abundant available substances in
nature. Water forms about 75% of the matter on earth’s crust. It
is an essential ingredient to all living organisms. More over, it
also enjoys a unique position in industries.
1.2
Sources of water
The chief sources of water fall into two main groups.
1. Surface water
2. Underground water
1.3
Hard water and soft water
Water is classified as soft water and hard water. This
is based on the reaction of water with soap solution.
Soft water
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.1
www.semesterplus.com
+
semester
www.semesterplus.com
Water that easily and readily forms lather with soap is
known as soft water.
Hard water
Water that does not produce lather with soap readily but
forms an insoluble precipitate like white scum is known as hard
water.
1.4
Classification of Hardness of water
Hardness of water can be defined as the soap consuming
capacity of water. Hardness of water can be classified into two
categories.
(i)
Temporary hardness (or) Carbonate hardness
(ii)
Permanent hardness (or) Non – Carbonate
hardness.
1.4.1. Temporary hardness (or) Carbonate hardness
This is caused by the presence of dissolved bicarbonates
of calcium, magnesium and other heavy metals.
Temporary hardness can be easily removed by means
of boiling of water. During boiling the bicarbonates are
decomposed into insoluble carbonate and hydroxides. This
insoluble carbonate and hydroxides will be removed by filtration.
Ca(HCO3)2
CaCO3 ↓+ H2O + CO2
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
www.semesterplus.com
+
semester
www.semesterplus.com
Insoluble
Mg(HCO3)2
1.4.2 Permanent
Mg(OH)2 ↓+ 2CO2
Insoluble
hardness
(or)
Non-Carbonate
hardness.
This is due to the presence of chlorides and sulphates of
calcium, magnesium, iron and other heavy metals.
Unlike temporary hardness, permanent hardness can not
removed on boiling.
It can be removed by chemical methods
demineralization process, zeolite process, reverse osmosis.
1.5
like
Boiler feed water
Water used in boilers to produce steam for power
generation is known as boiler feed water. The quality of water
used in the boiler should be pure. The boiler water should have the
following requirements.
Requirements
i)
The water should have zero hardness;
ii)
It should be free from corrosive gases;
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.3
www.semesterplus.com
+
semester
www.semesterplus.com
iii) It should be free from colloidal and suspended
impurities
1.6
Disadvantages of using Hard water in
Boilers
If hard water is used in boiler it will cause the
following problem
i)
Scale and sludge formation ii)
Boiler corrosion
iii)
Priming and foaming iv)
Caustic embrittlement
i)
Scale and sludge formation
Fig. 1.5 Sludge and Scale in Boiler
In boilers, water evaporates continuously and the
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
www.semesterplus.com
+
semester
www.semesterplus.com
concentration
of
the
dissolved
salts
increases
progressively. When their concentration reaches saturation
point, they are thrown out of water in the form of
precipitates on the inner walls of the boiler (Fig. 1.5).
Sludge: If the precipitate is loose and slimy, it is called
sludge.
Scale: If the precipitate is hard, adhering strongly in the
inner walls of the boiler, it is called scale.
1.12 Reason for the boiler scale or sludge
formation
Sludge:
Sludges are formed at comparatively colder portions of
the boiler and collects in areas, where the flow rate is slow or
at bends.
Substances that have greater solubility in hot water
than in cold water form sludges.
Example: MgCO3, MgCl2, CaCl2, MgSO4, etc.
Scale: Scales are formed due to
i)
Decomposition of calcium bicarbonate
Ca(HCO3)2
2CaCO3  + CO2 + 2H2O
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.5
www.semesterplus.com
+
semester
www.semesterplus.com
ii)
Solubility of CaSO4
The solubility of the salt CaSO4 decreases with rise of
temperature.
iii)
Temperature
CaSO4 Solubility
15o C
3200 ppm
230o C
55 ppm
320o C
27 ppm
Hydrolysis of magnesium salts
Magnesium salts hydrolyse at high temperature
forming insoluble hydroxides.
MgCl2 + 2H2O
iv)
Mg(OH) 2 + 2HCl
Presence of silica (SiO2)
Calcium and magnesium ions of hard water forms
silicate scale with silica.
1.12.1 Disadvantages of scale and sludge formation
Sludge:
i)
As they are poor conductor of heat, a portion of
heat generated is wasted.
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
www.semesterplus.com
+
semester
www.semesterplus.com
ii)
Excessive sludge formation disturbs the working of
the boiler.
Scale:
i)
Wastage of fuel
Scales are thermal insulator. So a considerable amount
of fuel may be wasted. Depending upon the thickness of the
scale formation, the wastage of the fuel may vary.
ii)
Thickness of scale(mm)
Wastage of fuel
0.325
10 %
1.25
50 %
12
150 %
Lowering of boiler safety
Due to the scale deposition on boilers, overheating of
the boiler tube is needed.
This makes the boiler material softer and weaker.
Hence distortion of boiler tube takes place. This makes the
boiler unsafe to bear the pressure of the steam in highpressure boilers.
Some of the salts mainly responsible for scale
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.7
www.semesterplus.com
+
semester
www.semesterplus.com
formation are CaCO3, CaSO4 and Mg(OH) 2.
iii)
Decrease in efficiency
Scales deposit in valves and condensers of the
boiler and choke them. This decreases the efficiency of the
boiler.
iv)
Danger of explosion
When cracks develop in scale, the water enters into the
crack and comes in contact with overheated iron plates. It is
immediately converted into steam. Thus, a sudden high
pressure is developed within the boiler. This high pressure
can cause explosion of boiler.
1.12.2 Removal of sludges and scales
Sludge can be easily removed
(i)
by scrapping with a wire brush
(ii)
by frequent blow down operation
Scales can be removed by the following methods.
i)
by thermal shocks (sudden heating and cooling)
ii)
using scrappers, brushes etc.
iii)
using certain chemicals.
iv)
Blow-down operation. This can be carried out by
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
www.semesterplus.com
+
semester
www.semesterplus.com
frequently removing bottom portion of
concentrated salt water of the boiler.
1.13 Boiler Corrosion
Boiler corrosion is decay of boiler material by a
chemical or electrochemical attack of its environment.
Main reason for boiler corrosion is,
1.
Dissolved Oxygen
Water contains 8ml of dissolved oxygen per litre at
35 C. It forms yellow rust [Fe2O3.2H2O] inside the boilers.
o
2Fe + 2H2O + O2
2Fe(OH)2
4Fe (OH)2 + O2
2[Fe2O3.2H2O]
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.9
www.semesterplus.com
+
semester
www.semesterplus.com
Fig.1.6 Deaeration of water
Removal of dissolved oxygen
(i) The formation of rust can be avoided by
removing the dissolved oxygen from the water. This can be
done by adding calculated amount of sodium sulphite or
hydrazine or sodium sulphide.
2Na2SO3 + O2
2Na2SO4
Sodium Sulphite
N2H4 + O2
N2 + 2H2O
Hydrazine
Na2S + 2O2
Na2SO4
Sodium sulphide
(ii) The removal of oxygen and CO2 from water can
also be done by mechanical deaeration.
In this method water is spraying in a perforated
plate-fitted tower (fig 1.6). Supply of heat from the sides and
the chamber is connected to vacuum pump. The development
of high temperature and low pressure in the tower reduces the
dissolved oxygen and CO2 in water.
2.
Dissolved Carbondioxide
The hydrolysis reaction of CO2, combined with H2O to
form weak carbonic acid which also involving in slow
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
www.semesterplus.com
+
semester
www.semesterplus.com
corrosion of boilers
CO2 + H2O
H2CO3 (carbonic acid)
Removal of CO2
The dissolved CO2 can be removed by adding weak
base ammonia.
2NH4OH + CO2
(NH4)2CO3 + H2O
ammonium carbonate
1.14 Priming and Foaming
Priming
When boiler is producing steam rapidly, some particles
of liquid water are carried along with the steam. This process
of wet steam formation is called priming.
Causes for priming
i)
The presence of large amount of dissolved solids ii)
High steam velocities
iii)
Sudden boiling
iv)
Improper boiler design
Prevention of priming
i)
Fitting mechanical steam purifiers
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.11
www.semesterplus.com
+
semester
www.semesterplus.com
ii)
Avoiding rapid change in steaming rate iii)
Maintaining low water levels in boilers
Efficient softening and filtration of the boiler feed
water
iv)
Foaming
Foaming is the production of persistent foam or
bubbles in boilers, which do not break easily.
Causes for foaming
It arises due to the presence of substances like oils,
alkali metal salts and suspended matters.
Prevention of foaming
i.
By adding sodium aluminate, alum and soda to the
boiler to remove oily materials
ii.
By adding anti-foaming agent like synthetic
polyamides
iii.
Oils can also be removed by electrophoresis
Priming and foaming usually occur together. They lead
to reduce the efficiency and decrease the life of the boiler. So
it should be prevented.
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
www.semesterplus.com
+
semester
www.semesterplus.com
1.15 Caustic Embrittlement
It is a type of boiler corrosion, caused by using alkali
water in boilers.
In lime soda process the softened water contains small
amount of Na2CO3, which under hydrolysis to form NaOH
(caustic soda) and CO2. This makes the boiler water caustic.
Na2CO3 + H2O
2NaOH + CO2
The NaOH containing water enters into the minute hair
cracks present in the inner wall of the boiler through capillary
action. Here water alone evaporates due to heating and
NaOH (caustic soda) concentration increases. This caustic
soda attacks the iron in the boiler to form sodium ferrate.
This causes caustic embrittlement of boiler parts
(particularly stressed parts like bends, joints, bolts, rivets,
etc.) leads to development of concentration cell. It causes
corrosion at anodic part.
+
Iron at
rivets, bends,
joints, etc
Iron at
Concentrated Dilute
NaOH solution NaOH solution plane surfaces
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.13
www.semesterplus.com
+
semester
www.semesterplus.com
Prevention of Caustic embrittlement
i)
By using sodium phosphate as softening reagent
instead of sodium carbonate.
ii)
By adding tannin, lignin or Na2SO4 to boiler water
since these blocks the hair cracks.
1.16 Boiler Feed Water Treatment
Boiler feed water should be mainly free from hardness
causing and scale forming impurities. The process of
removal of the dissolved salts from boiler water is known as
conditioning or treatment of water.
The boiler water can be treated by i)
Internal conditioning ii)
External conditioning iii)
Blow-down operation
1.17 Internal Treatment (or)
Internal Conditioning of water
This process is also called sequestration (complexing).
Internal treatment is adding a proper chemical to the boiler
water itself. This will cause either
CY 6251 – Engineering Chemistry II – Course material – Unit -
1.14
semester +
1.14
www.semesterplus.com
+
semester
www.semesterplus.com
i)
To precipitate the scale forming impurities in the
form of sludges. Sludges can be removed by blowdown operation (or)
ii)
To convert scale forming impurities into water
soluble compounds.
A number of internal treatment methods are available.
The important internal treatment methods are
1.
Phosphate Conditioning
In high pressure boilers, scale formation can be avoided
by adding sodium phosphate. This gives non- adherent and
easily removable soft sludge of Ca2+ and Mg2+.
3CaCl2 + 2Na3PO4
Ca3(PO4) 2 + 6NaCl
Three phosphates are usually used in this conditioning.
They are
1. Sodium dihydrogen phosphate (NaH2PO4) is used when
the alkalinity of water is too high (pH is above
10.5).
2. Disodium hydrogen phosphate (Na2HPO4) is used when
the alkalinity of water is moderate.
3. Sodium phosphate (Na3PO4) is used when the alkalinity
of water is very low.
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.15
www.semesterplus.com
+
semester
www.semesterplus.com
2.
Calgon Conditioning
Calgon is nothing but sodium hexa meta phosphate
Na2[Na4(PO3)6]. It prevents the scale and sludge formation by
forming complex with CaSO4.
Na2[Na4(PO3)6]
2CaSO4 + [Na4P6O18]23.
2Na+ + [Na4P6O18]2[Ca2P6O18]2- + 2Na2SO4
Carbonate conditioning
In low-pressure boilers, scale formation can be avoided
by adding Na2CO3 to boiler water. Hard water containing
CaSO4 is converted into CaCO3, a loose sludge.
CaSO4 + Na2CO3
CaCO3 + Na2SO4
1.18 External Conditioning
Water before feeding into boilers has to be treated for
hardness. This treatment of water is known as external
conditioning of water. The following external treatment
methods are used
i)
Ion-exchange process ii)
Zeolite process
iii)
Lime-soda process
CY 6251 – Engineering Chemistry II – Course material – Unit -
1.16
semester +
1.16
www.semesterplus.com
+
semester
www.semesterplus.com
1.19 Demineralization Process
exchange (or) De-ionization
(or)
lon-
In this method, ion exchange resins are used as
softening material. Synthetic resins are used as ion- exchange
resins or ion-exchangers.
Ion-exchangers have one ion adsorbed on it. These ionexchangers release this ion and adsorb another like ion. This
process is called ion-exchange adsorption.
Types of ion-exchangers
Ion exchange resins are insoluble, cross linked, long
chain organic polymers with a micro porous structure. The
functional groups attached to the chains are responsible for the
ion exchanging properties. There are two types of ion
exchangers.
1. Cation exchanger and
2. Anion exchanger
1.
Cation exchanger (RH)
When cations are exchanged, the ion-exchangers are
called cation exchangers. Resins containing acidic functional
groups (─COOH, ─SO3H) are capable of
exchanging their H+ ions with Ca2+ and Mg2+ ions present
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.17
www.semesterplus.com
+
semester
www.semesterplus.com
in hard water. Example: styrene divinyl benzene
copolymer.
Cation exchange resin
2. Anion exchanger (R'OH)
When anions are exchanged, the ion-exchangers are
called anion exchangers.
Resins containing basic functional groups
(CH3)3N+OH- are capable of exchanging their OH─ ions
with HCO3¯, Cl¯, SO4 2- ions present in the hard water.
CY 6251 – Engineering Chemistry II – Course material – Unit -
1.18
semester +
1.18
www.semesterplus.com
+
semester
www.semesterplus.com
Example: styrene divinyl benzene or amine formaldehyde
copolymers.
Ion exchangers are used in
(1) Zeolite or permutit process and
(2) Demineralization process (or) ion exchange (or)
deionization process for water softening.
In this process the hardness producing ions and all other
ions present in the hard water are replaced by H+ and OH–
ions and the water is demineralised.
Process
The hard water is allowed to pass through the cation
exchange column, which removes all the cations like Ca2+,
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.19
www.semesterplus.com
+
semester
www.semesterplus.com
2+
Mg from it.
2RH + Ca2+
2+
2RH + Mg
R2Ca + 2H
+
R2Mg + 2H
+
The water coming out from the cation exchanger column
2+
2+
(which is free from Ca and Mg ) is allowed to pass
through an anion exchanger column.
Fig. 1.7 Demineralization of water
All the anions like SO42–, Cl–, CO 32– etc., present in
the hard water are removed.
R’OH + Cl–
R’Cl + OH–
CY 6251 – Engineering Chemistry II – Course material – Unit -
1.20
semester +
1.20
www.semesterplus.com
+
semester
www.semesterplus.com
2R’OH + SO4
2–
R’2SO4 + 2OH
+
–
–
The H ions from cation exchange column and OH
ions from anion exchanger column combined to produce
water.
+
–
H + OH
H2O
Thus the water coming out of the anion exchanger is free
from both cations and anions. This water is known as ion-free
water or deionised or demineralised water.
Regeneration
After some time both the ion exchangers are exhausted
by using their respective H+ and OH- ions. The exhausted
cation exchange column is regenerated by
passing a solution of dil.HCl or dil.H2SO4
R2Ca + 2H+
2RH + Ca2+
R2Mg + 2H+
2RH + Mg2+
The outgoing washing contains CaCl2, MgCl2, MgSO4
is passed to sink.
The exhausted anion exchange column is regenerated
by passing a solution of dil.NaOH.
R’Cl + OH–
R’OH + Cl–
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.21
www.semesterplus.com
+
semester
www.semesterplus.com
–
2–
R’2SO4 + 2OH
2R’OH + SO4
The outgoing solution contains Na2SO4, NaCl etc., is
passed to sink.
Advantages
1.
The process is used to soften acidic and alkaline
water
2.
It produces water of very low hardness (2 ppm).
Disadvantages
1.
The equipment is costly. More expensive chemicals are
needed.
2.
If the water contains turbidity, the output is low due
clogging.
1.20 Zeolite (or) Permutit process Zeolite is
hydrated sodium alumino silicate,
[Na2OAl2O3xSiO2 yH2O; x =2 to 10 and y = 2 to 6].
It is represented as Na2Ze which is capable of
exchanging reversibly its sodium ions with hardness
producing ions in water. It is also known as permutits. These
are two types
i) Natural zeolites are non-porous
CY 6251 – Engineering Chemistry II – Course material – Unit -
1.22
semester +
1.22
www.semesterplus.com
+
semester
www.semesterplus.com
Example: Natrolite = Na2OAl2O3 4SiO2 2H2O
ii) Synthetic zeolites are porous and has gelly structure.
They are prepared by heating together china clay,
feldspar and soda ash. These zeolites have higher exchange
capacity per unit weight than natural zeolites.
Process
The hard water is allowed to percolate through a bed of
sodium zeolite (Na2Ze). The hardness causing ions (Ca2+,
Mg2+) in hard water is replaced by loosely held
sodium ions in zeolite bed. The outgoing soft water
contains sodium ions (Fig.1.8).
softner
Fig 1.8 Zeolite
During the softening the following reactions take place,
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.23
www.semesterplus.com
+
semester
www.semesterplus.com
Na2Ze + Ca(HCO3)2
Na2Ze + Mg(HCO3)2
Na2Ze + CaCl2
+ MgCl2
CaSO4
Na2Ze + MgSO4
CaZe + 2NaHCO3
MgZe + 2NaHCO3
CaZe + 2NaCl Na2Ze
MgZe + 2NaCl Na2Ze +
CaZe + Na2SO4
MgZe + Na2SO4
Regenaration
After the softening process, the zeolite is completely
converted into calcium and magnesium zeolites and it
gets exhausted. At this stage the hard water supply is stopped
and the exhausted bed is regenerated by treating with a
concentrated (10%) brine (NaCl) solution.
MgZe + 2NaCl
Na2Ze + MgCl2
CaZe + 2NaCl
Na2Ze + CaCl2
Exhausted Zeolite brine
regenerated Zeolite
Limitation of Zeolite Process
1) If the supplied water is turbid, the suspended matter
must be removed first by coagulation, filtration etc.
CY 6251 – Engineering Chemistry II – Course material – Unit -
1.24
semester +
1.24
www.semesterplus.com
+
semester
www.semesterplus.com
Otherwise, the turbidity will clog the pores of zeolite bed makes
it inactive.
2) If the water contains coloured ions (Mn2+, Fe2+ ) these ions
should be removed first. Because these ions produce manganese
and iron zeolite, which cannot be regenerated.
3) If any mineral acid is present in the water, it will destroy the
zeolite bed, therefore, it is neutralized first with soda (Na2CO3).
Advantages of Zeolite Process
1) Water quality of below 5 ppm hardness is obtained.
2) This equipment is compact and occupying small space.
3) The process automatically adjusts itself for variation in
hardness of incoming water.
4) It requires less time for softening.
5) It requires less skill for maintenance and operations.
6) No impurities are precipitated, so there is no danger of
sludge formation.
Disadvantages of Zeolite Process
1) The treated water contains more sodium salts than in lime
soda process.
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.25
www.semesterplus.com
+
semester
www.semesterplus.com
2) This method only replaces Ca2+ and Mg2+ ions by Na+, but
–
–
–
–
leaves all acidic ions (HCO3 , CO32 , Cl , SO42 )
3) When softened water (containing NaHCO3
and
Na2CO3) is used in boilers, these salts produce CO2 and
NaOH. This will cause corrosion and caustic
embrittlement.
1.21 Desalination
The process of removing common salt (NaCl) from the
brackish water is known as desalination.
The water containing dissolved salts with peculiar salty
taste is called brackish water. The common methods for the
desalination of brackish water are
i)
Reverse osmosis ii)
Electrodialysis iii)
Distillation and iv)
Freezing
(I)
Reverse Osmosis
When two solutions of unequal concentrations are
separated by a semi-permeable membrane the flow of
solvent takes place from dilute to concentrated sides, due to
osmosis.
CY 6251 – Engineering Chemistry II – Course material – Unit 1.26
semester +
1.26
www.semesterplus.com
+
semester
www.semesterplus.com
If however, a hydrostatic pressure excess of osmotic
pressure (15 to 40 cm) is applied on the concentrated
side, the solvent flow reverses. Solvent is forced to move from
concentrated side to dilute side across the membrane.
This principle is known as reverse osmosis.
Thus in reverse osmosis the pure water is separated (free
from ions) from the contaminated brine (salt) water. The semipermeable membrane is made of cellulose acetate,
polymethacrylate and polyamide polymers. This membrane
filtration is also called Super filtration or Hyper filtration.
(Fig.1.9)
Fig. 1.9 Reverse Osmosis
Advantages
i)
This method has greater advantages of removing
ionic, non-ionic, colloidal and high molecular
weight organic matter.
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.27
www.semesterplus.com
+
semester
www.semesterplus.com
ii)
iii)
The life time of membrane is quit high (2 years)
The membrane can be replaced within a few
minutes. It provides nearly uninterrupted water
supply.
iv)
Due to low capital cost, low operating cost and high
reliability, this method is superior to other methods.
Questions
1.
Explain the terms scales and sludges.
2.
How can the caustic embrittlement be prevented?
3.
Explain ion exchange process
4.
Explain demineralization process
5.
How the salts can be removed in reverse osmosis
process?
6.
Differentiate between scale and sludge
7.
Give Examples for external conditioning methods for
water treatment.
8.
What is breackish water?
9.
What is desalination?
10.
What is reverse osmosis?
CY 6251 – Engineering Chemistry II – Course material – Unit -
1.28
semester +
1.28
www.semesterplus.com
+
semester
www.semesterplus.com
11.
Calgon treatment prevents scale formation in
boilers. Give reason
12.
What is internal conditioning?
13.
What is hard water?
14.
What are zeolites?
15.
Define ppm.
16.
How will you estimate total hardness of water by
EDTA method?
17.
What are the requisites of boiler feed water?
18.
Discuss briefly the
hardwater in boiler.
19.
Explain with neat diagram the demineralization
process.
20.
What is desalination? Discuss any one desalination
process in details.
21.
Discuss briefly the different stages involved in the
treatment of domestic water.
22.
disadvantages
of
using
100 ml of a raw water sample on titration with N/50
H2SO4 required 12.0 ml of the acid to phenolphthalein
end point and 15.5 ml of the acid of methyl orange
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.29
www.semesterplus.com
+
semester
www.semesterplus.com
end point. Determine the type and extent of alkalinity
present in the water sample.
23.
A water sample is not alkaline to phenolphthalein but,
100 ml of the water sample on titration with
N/50 HCl, required 16.7 ml of methyl orange end point.
What are the types and amount of alkalinity present in
the water sample?
2 mark Questions
1.
Give
two
differences
between
hardness and permanent hardness.
temporary
2.
What are Sludges and Scales?
3.
Distinguish two types of hardness.
4.
What is desalination?
5.
Explain what is meant by soft water and hard
water. (Or) Distinguish two types of water.
6.
What is meant
advantage of
disinfectant?
7.
What is the principle of desalination of water by
reverse osmosis?
8.
Zeolite process can be used for treating brackish
water – True or False? Justify your answer.
by disinfectant? What is
using
chloramines
as
the
a
CY 6251 – Engineering Chemistry II – Course material – Unit -
1.30
semester +
1.30
www.semesterplus.com
+
semester
www.semesterplus.com
9.
What is calgon conditioning?
10.
Why is water softened before using in boiler?
11.
A water sample contains 120 mg of MgSO4 per lit.
Calculate the hardness in terms of CaCO3 equivalent.
12.
Why is it necessary to chlorinate drinking water
supply beyond break point?
13.
Write the mechanism of removal of calcium and
magnesium ions from hard water by calgon.
14.
Why is demineralized water preferred over
Zeolite method for use in boilers?
15.
What are the roles of phosphate in the internal
treatment of water?
CY 6251 – Engineering Chemistry II – Course material – Unit -I
semester +
1.31
www.semesterplus.com