it is a ppt on engineering chemistry one of the chapter

1. ENGINEERING CHEMISTRY
Sphoorthy Engineering College

2. ENGINEERING CHEMISTRY
 UNIT – I: Water and its treatment
 UNIT – II: Electrochemistry and Batteries
 UNIT – III: Polymers
 UNIT - IV : Fuels and Combustion
 UNIT - V : Cement, Refractories,
Lubricants and
Composites

3. After completing this course the student must demonstrate the knowledge and
ability to:
 Understand the basic properties of water and its usage in domestic and industrial
purposes.
 Extrapolate the knowledge of electrode, cell, anode, cathode, electromotive force
and reference electrodes.
 Identify the electrolytic cell and electrochemical cells with the different types of
batteries.
 Understand the basic principles of polymers. Explore the engineering applications
of polymeric materials
 Describe the combustion process of the fuels and the calorific values of the fuels.
 Justify the immense importance of basic constructional material, Portland cement in
civil engineering works.
 Describe the classification, properties and industrial applications of lubricants,
composites and refractories.
COURSE OUTCOMES

7. Soft water: Water, which produces lather with soap is called soft water.
ex: distilled water and rain water
Hard of water: Water, which does not produce lather with soap, but produces white
precipitate (scum) is called hard water. This is due to the presence of dissolved Ca
and Mg salts.
ex: bore well water, sea water
Water and its treatment
C17H35COONa H2O C17H35COOH NaOH
sodium stearate
(soap)
stearic acid
2 C17H35COONa CaCl2 (C17H35COO)2Ca 2NaCl
sodium stearate
(soap)
hardness
causing salt
calcium stearate
(scum)
water insoluble

8. Hardness is the property of water which does not produce lather with soap.
Causes of hardness of water:
The hardness of water is caused by the presence of dissolved salts such as
bicarbonates, sulphates and chlorides of calcium and magnesium.
Ca(HCO3)2 Mg(HCO3)2
CaSO4 MgSO4
CaCl2 MgCl2
Types of hardness: Hardness of water is two types.
1) Temporary hardness
2) Permanent hardness
Hardness of water

10. Ca(HCO3)2 CaCO3 H2O CO2
Temporary hardness: This is due to the presence of bicarbonates of calcium and
magnesium. It can be removed by boiling the water.
Permanent hardness: This is due to the presence of chlorides and sulphates of
calcium and magnesium. It cannot be removed by boiling the water. But can be
removed by (i) Lime soda process (ii) Zeolite process
CaCO3
CaCl2 Na2CO3
(soda)
2NaCl
CaSO4 Na2Ze
sodium zeolite
CaZe Na2SO4
Total hardness:
Total hardness = Permanent hardness + Temporary hardness

11. Expression of hardness: Hardness of water is expressed in terms of CaCO3
equivalents. CaCO3 is chosen as a standard because (i) the molecular weight of
CaCO3 is 100, which make calculations easy. (ii) CaCO3 is the most insoluble salt,
that can be precipitated in water treatment.
Amount of hardness causing salt x 100
CaCO3 equivalents =
Molecular weight of hardness causing salt
Expression & units of hardness
Units of hardness:
Parts per million (ppm)
Milligram per litre (mg/lit)
Clarke's degree (oCl)
French degree (oFr)

12. Parts per million (ppm): It is defined as the number of parts of CaCO3 equivalent
hardness per 106 parts of water.
1 ppm = 1 part of CaCO3 equivalent hardness in 106 parts of water
Milligram per litre (mg/lit): It is defined as the number of milligrams of CaCO3
equivalent hardness per one litre of water
1 mg/lit = 1 mg of CaCO3 equivalent hardness in one litre of water
Clarke's degree (oCl): It is defined as the number of parts of CaCO3 equivalent
hardness per 70000 parts of water.
1 oCl = 1 part of CaCO3 equivalent hardness in 70000 parts of water
French degree (oFr): It is defined as the number of parts of CaCO3 equivalent
hardness per 70000 parts of water.
1 oFr = 1 part of CaCO3 equivalent hardness in 105 parts of water
Relationship between various units:
1 ppm = 1 mg/lit = 0.07 oCl = 0.1 oFr
Units of hardness

13. If you plant a tree, you are making a statement that
you care for the world, the people, and life on the planet,
beyond yourself.......

14. Acid base titrations
Molarity =
Weight of the solute
Molecular weight of the solute Volume of the solution (in liters)
1
x
M =
wt
M.wt
x
1
V (in lit)
M =
wt
M.wt
x
1000
V (in ml)
(or)

15. Estimation of hardness of water by complexometric
method or EDTA method
Principle: The amount of hardness causing ions (Ca+2 and Mg+2) can be estimated
by titrating the water sample against EDTA using Eriochrome Black-T (EBT) indicator
at pH of 9-10. In order to maintain the pH, buffer solution (NH4Cl-NH4OH) is added.
Only at this pH such a complexation is possible. When the EBT indicator added to the
water sample, it forms wine red coloured unstable complex with Ca+2 and Mg+2 ions.
Ethylene diamine tetra acetic acid

16. When the solution is titrated against EDTA solution, EDTA replaces EBT from
unstable complex and forms a stable colourless complex and releasing blue coloured
EBT. Hence the colour change at the end point is wine red to blue colour.
EDTA
pH 9-10 Ca
Mg
EDTA
colourless stable complex
Ca
Mg
EBT
wine red coloured
unstable complex
EBT
(blue colour)
Ca+2
Mg+2
EBT
pH 9-10
Ca
Mg
EBT
(blue colour)
wine red coloured
unstable complex

17. Preparation of EDTA solution: It is prepared by dissolving 4 grams of EDTA in
1000 ml of distilled water.
Preparation of standard hard water: 1 gram of CaCO3 is dissolved in minimum
quantity of HCl and then made up to 1000 ml using distilled water.
1 ml of standard hard water = 1 mg of CaCO3 equivalent hardness
Preparation of EBT indicator: 0.5 grams of EBT is dissolved in 100 ml of ethyl alcohol
Preparation of Buffer solution: Add 67.5 grams of NH4Cl to 570 ml of ammonia (NH3)
solution and the solution is made up to 1000 ml using distilled water.
Preparation of reagents

18. Standardisation of EDTA solution: Rinse and fill the burette with EDTA solution.
Pipette out 20 ml of standard hard water into conical flask. Add 3-5 ml of buffer solution
and 2-3 drops of EBT indicator. Titrate with EDTA solution till wine red colour changes to
blue. Note the burette reading. Let the volume of EDTA consumed be "x" ml
Estimation of total hardness of water sample:
Pipette out 20 ml of the given hard water sample into a clean conical flask, add 3-5 ml of
buffer solution and 2-3 drops of EBT indicator. Titrate the wine red coloured solution with
EDTA solution till colour changes from wine red colour to blue.
Let the volume of EDTA consumed be "y" ml
Estimation of permanent hardness of water sample:
Take 100 ml of same hard water sample in a 250 ml beaker and boil till the volume reduces
to 20 ml. During boiling temporary hardness gets removed. Cool and filter the solution and
make up the volume to 100 ml with distilled water. Pipette out 20 ml from the above water
sample (boiled water), add 3-5 ml buffer solution and 2-3 drops of EBT indicator. Titrate with
EDTA solution till the wine red colour changes to blue. Note the burette reading.
Let the volume of EDTA consumed be "z" ml

19. Molarity of standard hard water (M1) =
weight of CaCO3
molecular weight of CaCO3
volume of the solution in liters
x
1
= x
M1
1
100
1
1
= 0.01 M
M1V1 = M2V2 M2 =
M1V1
V2
=
0.01 X 20
x
Calculations
V1 = Volume of standard hard water
M2 = Molarity of EDTA solution
V2 = Volume of EDTA solution
Standardisation of EDTA

20. M3 = Molarity of hard water = ?
V3 = Volume of hard water = 20 ml
M4 = Molarity of EDTA solution = M2
V4 = Volume of EDTA solution = "y" ml
M3V3 = M4V4 M3 =
M4V4
V3
=
M2 X y
20
gram/lit
Total hardness of water = M3 X 100 gm/lit
Total hardness of water = M3 X 100 X 1000 mg/lit
Total hardness of water = M3 X 100 X 1000 ppm
Total hardness of water =
M2 X y X 100 X 1000
20
ppm
ppm
Total hardness of water =
Molarity of EDTA x Volume of EDTA x 100 x 1000
Volume of hard water
Estimation of total hardness of water sample

21. M5 = Molarity of hard water = ?
V5 = Volume of hard water = 20 ml
M6 = Molarity of EDTA solution = M2
V6 = Volume of EDTA solution = "z" ml
M5V5 = M6V6 M5 =
M6V6
V5
=
M2 X z
20
gram/lit
Permanent hardness of water =
M2 X z X 100 X 1000
20
ppm
Molarity of EDTA x Volume of EDTA x 100 x 1000
Volume of hard water (containg permanent hardness)
Permanent hardness of water = ppm
Estimation of permanent hardness of water sample

22. Total hardness:
Total hardness = Permanent hardness + Temporary hardness
Temporary hardness = Total hardness - Permanent hardness

23. 1. Temporary hardness of water is due to the presence of
(a) Mg(HCO3)2 (b) MgCl2 (c) CaCl2 (d) NaCl
2. What is the unit to measure the hardness of water?
(a) Kg (b) oC (C) ppm (d) none
3. Which one is the wrong sentence
(a) Hard water does not produce leather with soap
(b) Temporary hardness can be removed by boiling the water
(c) Permanent hardness can be removed by boiling the water
(d) Permanent hardness is due the presence of chlorides & sulphates of Mg and Ca

24. The water used for drinking purposes is called potable water.
The important characteristics of potable water are:
 It should be clear, colourless and odourless
 It should be cool and pleasant in taste
 It should be free from dissolved gases like H2S and poisonous minerals like
lead, arsenic, chromium, manganese etc.,
 It should be free from harmful bacteria, virus and fungus.
 Turbidity of the water should be less than 10 ppm.
 Its total dissolved solids (TDS) must be less than 500 ppm.
 pH of the water should be between 6.5-8.5
Potable water and its specifications

25. Screening: It is a process of removing the floating materials like leaves, wood pieces
etc from water. The raw water is allowed to pass through a screen, having large
number of holes, which retain the floating materials and allows the water to pass.
Sedimentation: It is a process of removing suspended impurities by allowing the
water to stand for 2-6 hours in a big tank. Most of the suspended particles settle down
at the bottom due to the force of gravity.
Coagulation: The process of settlement of small suspended impurities by adding some
chemicals like alum is called coagulation and chemicals used are called coagulants.
Coagulants like alum provide Al+3 ions, which neutralise the negative charge on the
colloidal clay particles. After losing the negative charge, the tiny particles come nearer
to one another and combine to form bigger particles, which settle down due to the
force of gravity.
Steps involved in the treatment of potable water
Al2(SO4)3.18H2O 3Ca(HCO3)2 2Al(OH)3 3CaSO4 18H2O 6CO2

26. Filtration: After sedimentation and coagulation the water is passed through sand filter.
The sand filter consists of a tank containing a thick top layer of fine sand followed by
coarse and gravel.
water
Fine sand
Coarse sand
gravel
Sand filter
Filtered water

27. The process of removing disease causing microorganisms from water is called
disinfection or sterilisation. The following methods are used for the disinfection of
water.
Boiling: When water is boiled for 10-15 minutes, all the disease causing microorganism
are killed and water becomes safe for use.
This method is useful for domestic purpose but is not suitable for sterilisation of large
amounts of water.
Exposure to UV: UV rays kills the harmful bacteria present in the water. This method
is effective but involves high cost.
By ozonation: Passage of ozone through water kills the harmful germs due to the
release of nascent oxygen. This process is highly expensive and hence, not employed
for disinfection of municipal water. Ozone is unstable and cannot be stored for long
time.
Disinfection or sterilisation
O3
O2 O
Bacteria O Bacteria killed

28. Chlorination: The process of adding chlorine to water is called chlorination. Chlorination can
be done by the following methods.
(1). By adding bleaching powder:
When bleaching powder(CaOCl2) is added to water it produces hypochlorous acid (HOCl).
HOCl is a powerful disinfectant.
(2). By using chloramine (ClNH2):
When chlorine and ammonia are mixed in the ratio of 2:1 by volume, a compound chloramine
is formed. Chloramine on reaction with water produces hypochlorous acid, which is a powerful
disinfectant.
CaOCl2 Ca(OH)2
Bacteria Bacteria killed
H2O Cl2
HOCl
Cl2 H2O HCl
HOCl
Cl2 HCl
NH3
H2O NH3
HOCl
ClNH2
chloramine
ClNH2

29. 3). By adding chlorine gas:
When chlorine gas bubbled in the water it produces hypochlorous acid (HOCl), which
is a powerful disinfectant.
Bacteria Bacteria killed
HOCl
Cl2 H2O HCl
HOCl

30. The amount of chlorine required to kill the bacteria and to remove organic and
reducing compounds from water is called break point chlorination.
 When chlorine is added to water, number of reactions taking place in water and the
residual chlorine in water is also changing (increasingly as well as decreasingly).
 Initially the applied chlorine is used to kill the bacteria and oxidises all the reducing
substances (Fe+2, Mn+2, H2S etc.,) present in the water and there is no free residual
chlorine in the water.
 As the amount of applied chlorine increases, it reacts with ammonia and other
organic compounds present in the water and forms chloramines and chloro organics,
so the combined residual chlorine also increases.
 At one point, on further chlorination, the destruction of chloramines and chloro
organics starts and there is a fall in combined residual chlorine.
 The point C at which the total chlorine demand is satisfied, as any chlorine added
to water beyond this point, breaks through the water and appears as residual chlorine.
 This point C is called break point. The addition of chlorine beyond break point is
called break point chlorination.
Break point chlorination

31. Advantages of break point chlorination:
(1) It removes or destroys the organic compounds, ammonia and reducing
compounds from the water.
(2) It removes colour and odour from the water
(3) It kills the harmful bacteria.

32. Defluoridation is the removal of excess fluoride from water. The acceptable
Fluoride limit in drinking water is <1 mg/lit.
Defluoridation
Fluoride is said to protect the teeth in two ways: Protection from demineralization -
when bacteria in the mouth combine with sugars they produce acid. This acid can
erode tooth enamel and damage our teeth. Fluoride can protect teeth from
demineralization that is caused by the acid

34. Nalgonda Technique:
National Environment Engineering Research (NEERI), Nagpur has evolved an economical and
simple method for removal of fluoride which is referred to as Nalgonda technique.
 Nalgonda Technique involves addition of aluminium salts, lime/soda and bleaching powder
followed by rapid mixing, flocculation, sedimentation, filtration and disinfection.
 Aluminium salt may be added as aluminium sulphate or aluminium chloride or combination of
these two. Aluminium salt is only responsible for removal of fluoride from water.
 The dose of aluminium salt increases with increase in the fluoride and alkalinity levels of the
raw water. The selection of either aluminium sulphate or aluminium chloride also depends on
sulphate and chloride contents of the raw water to avoid them exceeding their permissible
limits.
The dose of lime is empirically 1/20th that of the dose of aluminium salt. Lime facilitates
forming dense floc for rapid settling. Bleaching powder is added to the raw water at the rate of
3 mg/l for disinfection.
Defluoridation: Nalgonda Technique

35. Fill and draw technique for small communities:
 For communities with a population ranging from 200 to 2000, a defluoridation plant
of fill and draw type is recommended.
 The plant consists of a hopper-bottom cylindrical tank with a depth of 2m. The
diameter depends upon the quantity of the water to be treated.
 All unit operations of mixing, flocculation and sedimentation are performed in the
same vessel.
 It has a stirring mechanism, which can be either hand operated or power driven.
 Raw water is pumped to the unit and required quantity of alum, lime and bleaching
powder are added. The contents are stirred for 10 min and allowed to settle for
1-2 hours. The settled sludge is discarded and the defluoridated supernatant is filtered
and supplied through stand posts.

36. Nalgonda technique for domestic defluoridation: Any container of 20-50 lit capacity
is suitable for this purpose. A tap, fitted 3-5 cm above the bottom of the container is
useful to withdraw treated water but is not essential.
 Adequate amount of lime water and bleaching powder are added to raw water and
mixed well. Alum solution is added to it and stirred for 10 min.
The contents are allowed to settle for 1 hour and the clear water is withdrawn either
through the tap or decanted slowly, without disturbing the sediment and filtered.

37.  The chemicals required are readily available and are used in conventional municipal
water treatment.
 Adaptable to domestic use.
 Economical
 Can be used to treat water in large quantities for community usage.
 Simplicity of design, construction, operation and maintenance.
 Local semi-skilled workers can be readily employed.
 Highly efficient removal of fluorides from high levels to desirable levels.
 Simultaneous removal of colour, odour, turbidity, bacteria and organic contaminants.
 Little wastage of water and least disposal problems.
 Needs minimum of mechanical and electrical equipment.
 No energy, except muscle power is required for domestic equipment
Disadvantages of Nalgonda technique:
 Large amount of alum needed to remove fluoride.
 Careful pH control of treated water is required.
 High residual aluminium is reported in treated water.
Advantages of Nalgonda technique

38. Sewage: Sewage is the term used for waste water that often contains human and house
hold waste water, industrial waste water, ground wastes, street washings and storm
water.
Sewage, besides 99.9% water, contains organic and inorganic matters in dissolved,
suspension and colloidal states.
Sewage (waste water) contains both aerobic and anaerobic bacteria. These bacteria can
make the oxidation of organic compounds present in the sewage.
Sewage

39. Aerobic oxidation and anaerobic oxidation:
In the presence of good amount of dissolved or free oxygen, organic compounds in
sewage undergo a process of oxidation brought about by aerobic bacteria and oxidation
products are inoffensive smelling, non-putrefying nitrites, nitrates, sulphates etc. This
kind of oxidation is called aerobic oxidation.
On the other hand, when the dissolved or free oxygen supply is below a certain value,
the sewage is called stale and anaerobic bacteria bring about putrefaction, producing
methane, hydrogen sulphide and phosphine, which give offensive odour. This kind of
oxidation of sewage is called anaerobic oxidation.
H2N
C
NH2
O aerobic oxidation
CO2 2NH3
NH3
aerobic oxidation HNO3, HNO2
HNO3, HNO2
base
NH4NO2, NH4NO3, KNO2

40. Biological oxygen demand (BOD): BOD is defined as amount of free oxygen
required for the biological oxidation of the organic matter in a sewage sample under
aerobic conditions at 20 oC and for a period of 5 days.
The unit of BOD is mg/lit or ppm.
The BOD is an important measure of water quality, as it indicates the amount of
decomposable organic matter in the sewage.
Chemical oxygen demand (COD): COD is defined as the amount of oxygen required
to oxidise organic matter in a sewage sample by chemical oxidation with a powerful
oxidising agent such as potassium dichromate.

41. Sewage treatment generally involves four stages, called pre, primary, secondary and
tertiary treatment.
Screening (pre-treatment): In this process waste water is passed through bar screens
which removes large floating matter. Then water is passed through a grit chamber, in
which the velocity of water flow is reduced to a point where the denser sand and other
grit will settle out. The removed solid material in this process is buried or used to fill.
Sedimentation or settling process (primary treatment): Settling process removes
larger proportion of the suspender organic solids from the sewage. For this large
sedimentation tanks are employed, in which solids settle out of water by force of
gravity where the settle-able solids are pumped away (as sludge), while oils float to the
top are skimmed off. Chemical treatment is sometimes given to sewage for more rapid
and complete removal of suspended matter. Coagulants such as alum, ferrous sulphate
etc are used for this purpose.
Sewage treatment

42. Biological or secondary treatment process: It is a biological oxidation (aerobic
oxidation) process. It is achieved by the use of biological film system (trickling
filter) and activated sludge system. During aerobic oxidation process, the carbon of
the organic matter is converted in to CO2, the nitrogen into NH3 and finally into
nitrates and nitrites. The dissolved bases present in the sewage then form salts such
as ammonium nitrite, ammonium nitrate, potassium nitrite etc.
H2N
C
NH2
O aerobic oxidation
CO2 2NH3
NH3
aerobic oxidation HNO3, HNO2
HNO3, HNO2
base
NH4NO2, NH4NO3, KNO2

43. Activated sludge process: In this process adequate amount of oxygen or air is passed
through waste water containing aerobic bacteria.
Complete aerobic oxidation occurs, though slowly. However, if this aeration is carried
out in the presence of a part of sludge from the previous oxidation process, the
oxidation is much faster. This added sludge from the previous process is known as
activated sludge, since it contains numerous aerobic bacteria.
In this process, the sedimented waste water is mixed with proper quantity of activated
sludge and the mixture is then sent to aeration tank, in which the mixture is
continuously aerated and agitated for 4-6 hours. During this aeration process, oxidation
of the organic matter takes place. After aeration the effluent is sent to sedimentation
tank, where sludge is allowed to settle out and the water moves for further treatment or
discharge.
Activated sludge process

44. Treated
effluent
Excess sludge
air
sludge
Aeration tank Sedimentation tank
Primary
effluent
Activated sludge process

45. Trickling filters are either rectangular or circular in shape and about 1-3 meters
deep.
Trickling filter consist of a filter bed made of furnace slag/crushed rock/anthracite
coal/broken bricks/shredded PVC bottles with loose packing so as to facilitate
circulation of air.
 The bed is covered with biological slime consisting of bacteria. The water is trickles
or sprayed over the filter bed. As the water migrates through the pores of the filter,
dissolved organic matter degrades (oxidised) by the microorganisms. The purified
water is removed from the bottom.
Biological film system (trickling filter)

46. Biological film system (trickling filter)

47. Advanced treatment or tertiary treatment: Tertiary treatment is the most advanced
phase of treatment and its objectives are to decrease the phosphorous, nitrogen
compounds in the effluents and also to remove the pathogens.
By treating effluent from secondary treatment with calcium oxide forms insoluble
calcium phosphate, which can be filtered off. Then ammonia removed using air
stripping technology. Finally effluent is chlorinated to kill the harmful pathogens.
Sludge digesters & drying beds: The sludge which settles in the sedimentation tanks
is pumped to the digesters where a temperature of 30-35 oC is maintained. This is the
optimum temperature for anaerobic bacteria. The usual length of digestion is 20-30
days. When anaerobic decomposition takes place, gases like methane (60%), hydrogen
sulphide etc., will be generated, which can be used as fuel.
Digested sludge is placed on drying beds of sand where the liquid may evaporate or
drain into the soil. The dried sludge is a porous humus like cake which can be used as a
fertiliser.

49. In boilers, water continuously converted in to steam, resulting increase in
concentration of the dissolved salts.
When their concentrations reach saturation point, the dissolved salts start precipitating
out.
If the precipitation takes place in the form of loose and slimy precipitate, it is
called sludge. On the other hand, if the precipitated matter forms a hard, adherent
coating on the inner walls of the boiler, it is called scale.
Boiler troubles

50. Sludge:
Sludge is a soft, loose and slimy precipitate formed within the boiler. Sludge’s are formed by
substances like MgCO3, MgCl2, CaCl2, MgSO4 and they have greater solubility in hot water than
in cold water.
Disadvantages of sludge formation:
1. Sludge’s are poor conductors of heat and thus a portion of heat is wasted.
2. If sledges are formed along with scales, then it gets entrapped and deposited along with
scales.
3. Excessive sludge formation disturbs the working of the boiler. It may choke the boiler pipes.
Prevention of sludge formation: Sludge formation can be prevented
(1) by using softened water,
(2) by frequently ‘blow-down operation', i.e., removing a portion of the concentrated water and
replacing with fresh water.

53. Scales are hard deposits, which stick very firmly to the inner surfaces of the boiler.
The main scale forming substances are Ca(HCO3)2, CaSO4, Mg(OH)2.
Reasons for formation of scales
1. Decomposition of calcium bicarbonate:
Calcium bicarbonate decomposes to an insoluble CaCO3. In low pressure boilers
CaCO3 is the main cause of scale formation. But in high-pressure boilers, CaCO3 is
soluble.
Ca(HCO3)2 CaCO3 ↓ + H2O + CO2 ↑ low pressure boilers
(Scale)
CaCO3 + H2O Ca(OH)2 + CO2 ↑ high-pressure boilers
(soluble)
2. Deposition of CaSO4:
Calcium sulphate is soluble in cold water, but solubility decreases with increase in
temperature (solubility of CaSO4 is 3,200 ppm at 15oC and it reduces to 27 ppm at
320oC). At high temperature in boilers calcium sulphate get deposited as hard scale.
Scale

54. 3. Hydrolysis of magnesium salts : Dissolved magnesium salts undergo hydrolysis at
high temperature inside the boilers and forms magnesium hydroxide precipitate.
MgCl2 + 2 H2O → Mg(OH)2 ↓ + 2HCl
(Scale)
4. Presence of silica (SiO2): The small quantities of silica present in water, deposits as
calcium silicate (CaSiO3) and magnesium silicate (MgSiO3).
These are very hard scales.
Disadvantages of scale formation:
(1) Wastage of fuel : Scales have a low thermal conductivity, so the rate of heat
transfer from boiler to inside water is greatly decreased. In order to provide a steady
supply of heat to water, over heating is carried out and this causes increase in fuel
consumption.
(2) Lowering of boiler safety : Due to scale formation, over-heating of boiler is to be
done in order to maintain a constant supply of steam. The over-heating of the boiler
makes the boiler material softer and weaker and this causes distortion of boiler tube and
makes the boiler unsafe to bear the pressure of the steam, especially in high-pressure
boilers.
(3) Danger of explosion : When the scale cracks, water suddenly comes in contact
with over-heated iron plates. This causes formation of a large amount of steam
suddenly. So sudden high-pressure is developed, which may even cause explosion of
the boiler.

55. Prevention of scale formation: Scale formation can be prevented
(1) by using softened water.
(2) by internal treatment of water.
Removal of scales: Scales can be removed by mechanical and chemical methods.
Mechanical methods:
(i) With the help of scraper or wire brush, if they are loosely adhering.
(ii) By giving thermal shocks (i.e., heating the boiler and then suddenly cooling
with cold water), if they are brittle.
(iii) By frequent blow-down operation, if the scales are loosely adhering.
Chemical methods
If they are adherent and hard they can be removed by chemical treatment. 5-10% HCl
can remove CaCO3 scale and EDTA(ethylene diamine tetra acetic acid) can remove
CaSO4 scale.

56. The formation of cracks in the boiler due to high concentration of NaOH is called
caustic embrittlement.
Boiler water (treated by lime soda process) usually contains a small amount of Na2CO3.
In high pressure boilers, Na2CO3 decomposes to give sodium hydroxide and this makes
the boiler water basic ["caustic"].
Na2CO3 + H2O 2NaOH + CO2
 This NaOH containing water flows into the minute hair-cracks present in the inner
side of boiler, by capillary action. Here, water evaporates and the dissolved caustic
soda concentration increases progressively.
 This caustic soda attacks the surrounding area, thereby dissolving iron of boiler as
sodium ferroate this causes embrittlement of boiler parts, particularly stressed parts
like bends, joints, rivets etc., causing even failure of the boiler.
Fe + 2NaOH Na2FeO2 + H2
Caustic embrittlement

57. Caustic embrittlement can be prevented
 by using sodium phosphate as softening agent, instead of sodium carbonate
 by adding tannin or lignin to boiler water, since these blocks the hair-cracks.
Prevention of Caustic embrittlement:

58. Colloidal conditioning: In low-pressure boilers, scale formation can be avoided by
adding colloidal conditioning agents like kerosene, tannin, agar-agar etc. These
colloidal substances get coated over the scale forming particles and convert them into
non-sticky and loose precipitate called sludge, which can be easily removed by blow
down operation.
Internal treatment of boiler feed water
Phosphate conditioning: In high-pressure boilers, scale formation can be avoided by
adding sodium phosphate, which reacts with Ca+2 and Mg+2 salts to give soft sludge
of calcium and magnesium phosphates, which can be removed by blow - down
operation.
3CaCl2 + 2Na3PO4 Ca3(PO4)2 + 6 NaCl
The main phosphates employed are:
(a) NaH2PO4 (sodium dihydrogen phosphate) is used for alkaline water
(b) Na2HPO4 (disodium hydrogen phosphate) is used for weakly acidic water
(c) Na3PO4 (trisodium phosphate) is used if the water is too acidic.

59. Calgon conditioning:
The word "calgon" means calcium gone i.e., the removal of Ca+2. Sodium hexa meta
phosphate is called calgon. It prevents the scale formation by forming soluble
compound with CaSO4.
Na2[Na4(PO3)6] + CaSO4 Na2[Ca2(PO3)6] + 2Na2SO4
calgon Soluble complex

60.  This process removes almost all the ions (both cations and anions) present in the
water.
 Demineralisation process is carried out by using ion exchange resins, which are
long chain, cross linked, insoluble organic polymers with a micro porous structure.
 The functional groups attached to the chains are responsible for the ion exchange
properties. The ion exchange resins are two types.
Cation exchange resins (R-H)
Anion exchange resins (R-OH)
Cation exchange resins: Resins containing acidic functional groups (-COOH, -
SO3H) are capable of exchanging their H+ ions with the cations present in the water.
R-COOH, R-SO3H ≡ R-H
Anion exchange resins: Resins containing basic functional groups (-OH) are capable
of exchanging their OH- ions with the anions present in the water.
R-OH
Ion Exchange or Demineralisation Process

61. Process: The hard water is first passed through cation exchanger, which removes all
the cations like Ca+2, Mg+2, Na+ etc., present in the water and equivalent amount of H+
ions are released from this exchanger to water.
2R-H + Ca+2 R2Ca + 2H+
2R-H + Mg+2 R2Mg + 2H+
R-H + Na+ RNa + H+
After cation exchanger, the water is passed through anion exchanger, which removes
all the anions like CO3
-2, SO4
-2, Cl- etc., present in the water and equivalent amount of
OH- ions are released from this exchanger to water.
2R-OH + CO3
-2 R2CO3 + 2OH-
2R-OH + SO4
-2 R2SO4 + 2OH-
R-OH + Cl- RCl + OH-
H+ and OH- ions (released from cation and anion exchangers respectively) get
combined to produce water molecule.
H+ + OH- H2O

62. Thus the water coming out from the exchanger is free from all the ions. Ion free
water is known as de-ionized or de-mineralised water.
Regeneration: After de-mineralisation of water, the ion exchangers get exhausted.
The exhausted cation exchangers are regenerated by dilute HCl and the exhausted
anion exchangers are regenerated by dilute NaOH.
R2Ca + HCl 2R-H + CaCl2 (washed)
R2CO3 + NaOH 2R-OH + Na2CO3 (washed)
Advantages:
(1). It produces water of very low hardness (2 ppm).
(2). Operation expenses are less.
(3). Heating is not needed.
Disadvantages:
(1). Capital cost is high.
(2) Turbid water cannot be treated. The turbidity must be below 10 ppm.

63. dil. NaOH
Anion exchange resin
dil. HCl
Raw water
Cation exchange resin
drain
drain
De-ionised water

64. Desalination: The process of removal of dissolved salts present in the water is known
as desalination.
Depending upon the quality of dissolved solids, water is divided into 3 categories.
(1). Fresh water: contains < 1000 ppm of dissolved solids.
(2). Brackish water: contains >1000-35000 ppm of dissolved solids.
(3). Sea water: contains >35000 ppm of dissolved solids.
Desalination

65. Osmosis: The process of transfer of solvent from dilute solution to a concentrated
solution through a semi-permeable membrane is called "osmosis".
ex: plants absorb water from the soil by the osmosis only.
 Semi-permeable membrane allows only solvent (water) molecules to pass through
but not solute.
ex: egg membrane, cell membrane.
Osmosis
o = solute
Osmotic pressure: The external pressure applied on high concentrated solution side
just to stop the osmosis is called osmotic pressure.

66. Reverse osmosis: The process of forcing "solvent" from more concentrated solution
to a less concentrated solution through a semi-permeable membrane by applying a
pressure more than osmotic pressure is called reverse osmosis.
Method of purification: The sea water & pure water are taken in a container and
separated by a semi-permeable membrane. If high pressure (15-40 kg/cm2) is applied
on the sea water, the pure water is passed through the semi-permeable membrane. The
semi-permeable membrane is made of cellulose acetate.

67. Sea water
Pure water
Semi permeable membrane
pressure
piston
Pure water

68. Advantages:
(1). This process removes ionic as well as non ionic dissolved impurities.
(2). This process is cheap and convenient.
(3). It is suitable for converting sea water into drinking water.
(4). The semi-permeable membrane can be replaced within few minutes and the
membrane life time is nearly two years.

69. 1. Tanin and Lignin are used for
(a) Phosphate conditioning (b) Carbonate conditioning
(c) Colloidal conditioning (d) Calgon conditioning
2. Calgon trade name given to
(a) Sodium hexameta phosphate (b) Magnesium phosphate
(C) Calcium phosphate (d) Sodium phosphate
3. Calgon trade name given to
(a) Sodium hexameta phosphate (b) Magnesium phosphate
(C) Calcium phosphate (d) Sodium phosphate
4. Caustic embrittlement is caused due to the presence of
(a) NaCl (b) NaOH (c) MgCO3 (d) KNO3
5. In Ion exchange process regeneration of cationoic resin is done by treating
with................
6. The process of killing pathogens from water is called.....................
7. The process of removal of common salt from water is called...................