2024 Pattern SPPU

Engineering Chemistry
UNIT -1 WATER TECHNOLOGY

Types of Impurities:
I.DissoIved Impurities:
a) Inorganic salts e.g. bicarbonates, sulphates ,nitrates ,chlorides of calcium, Magnesium,
Iron, Mn, Al etc
b)Gases- like carbon dioxide, nitrogen , oxygen, hydrogen sulphides
Removal Method: Mechanical deaerators & Chemical treatment
2. Suspended Impurities:
a) Clay
b) mud
c) Vegetable and animal matters

Removal Method: Filtration & Sedimentation / Settlement

3.CoIIoidaI Impurities:
a) fine size like silica and alumina, organic wastes etc.
These are soluble materials, other than gases cannot be
removed by conventional filters referred as TDS which

stands for total dissolved solids.

Removal Method : Coagulation followed by Filtration & Sedimentation

4.BacteriaI Impurities:
a) Bacteria, Germs, Pathogens, Microbes, Viruses, Parasites includes - algae, beneficial
bacteria that decompose wastes harmful bacteria such as those that cause cholera.

Removal Method : Filtration followed by Sterilization

*Hardness of water:
Hardness character to water, is due to presence of dissolved salts of heavy metals like
++,Mn++ Al+3 .
 • If carbonate, bicarbonate, sulphate, nitrate and chloride salts of bivalent cations such
as Mg++, Fe 2+, Mn 2+, Ca 2+ are present in water, then the hardness of water is high
as
compared to that due to presence of salts of monovalent cations such as K+ and Na+ ,Li+
(light metal) .
1)Soft water-Water that gives lather with soap easily and readily is called Soft water.
OR Water which produce lather /foam with soap solution ,but does not develops
curd/scum is called as hard water.
2)Hard water- Hard water forms scum when it comes in contact with water.
OR Water which does not produce lather /foam with soap solution, but develops
curd/scum is called as hard water.

UNIT Of Hardness of water:

CaC03 eq. for any salt = Mass of any salt x 50/Eq. wt of any salt

• Miligram per liter (mg / lit): Number of milligram of CaC03 present in 1 lit of
water.
1 ppm = 1 part of CaC03 equivalent/106 parts of water.

• Parts Per Milion (ppm): Number of parts by wt of CaC03 present in million parts by
wt of water.
1 ppm = 1 mg/lit.

Types of Hardness of water:

1) Temporary Or Carbonate Hardness/AIkaIine Hardness : Water that contains bicarbonate of
calcium and magnesium or of both salts of heavy metals is called as Temporary Or Carbonate
Hardness.

e.g Salts such as ,MgC03, FeC03.

Removed by boiling

CaC03 + C02 T+ 1-120

Mg (OH)2 + 2C02
2)Permanent /Non- Carbonate Hardness/Non-AIkaIine Hardness: Water due to dissolved
salts present in water like chlorides or sulphate& nitrates of calcium or magnesium ,Fe,Mn,
Al (heavy metal) is called as Permanent /Non- Carbonate Hardness

• e .g Salts such as caC12 , MgS04, MgC12,CaS04,

• It can not be removed by boiling.

 caC12 Ca+2 + 2Cl-1 MgS04
+ Mg+2 +

Determination of Water Hardness By EDTA Method

(Complexometric Titration):
Theory:
1. Na2EDTA: Na2EDTA is highly sensitive towards heavy metal ions in water and easily
reacts with heavy metal .
2. pH =10 :During reaction of disodium EDTA & heavy metal in water H + ions are
formed & decrease the pH of reaction mixture, hence a buffer solution of pH is
necessary and to avoid reversible reaction .
3. Complexometric titration: Reaction of disodium EDTA & heavy metal ion ,results in
the formation of cyclic co-ordination complex (chelate) ,hence the titration is known
as complexometric titration.

4. EBT: EBT act as indicators for the EDTA titrations.

Principle
The hardness causing ions like Ca++,Mg++ presents in water form stable chelate complexes
with disodium EDTA ,at suitable pH, and indicators give sharp end point.

- At endpoint EBT—M ion complex breaks, and EDTA forms complex with released
M ion. EBT is set free giving blue color.

- Reaction :
i) M++ + EBT M-EBT +2 H
pink red/wine red (unstable complex)
ii) M++ + EDTA --> M-EDTA +2 1-1+
colorless (stable complex)
iii
)M-EBT + EDTA* VI-EDTA + EBT
colorless sky blue

HOOC.H2C CH2COOH
N — CH2 - CH2-N
NaOOC.H2C CH2COONa
 11
2—

11

M-EDTA complex / chelate

Procedure:
Part I: Standardization of NaÆDTA Vs MgS04
• 25 ml SHW + 10 ml buffer (pH 10) + 2—3 drops EBT indicator
—wine red color— titrated against NaÆDTA solution till sky
blue.
Solution in Burette: NaÆDTA solution.
Solution in pipette: 25 ml MgS04 solution
Indicator: 2—3 drops EBT
Conical flask: Above 25 ml hard water + 10 ml buffer (pH 10) +2—3 drops EBT
End Point: wine red to sky blue
Burette Burette reading: ' X ' ml or VI ml
Part Il:TotaI hardness of sample water Vs NaÆDTA

• 50 ml Sample Hard Water + 10 ml buffer (pH 10) + 2—3 drops

EBT indicator —wine red color —titrated against NaÆDTA
solution till sky blue.

• Solution in Burette: Na2EDTA solution.

• Solution in pipette: 50 ml hard water
Indicator: 2-3 drops EBT
Conical flask: Above 25 ml hard water + 10 ml buffer (pH 10) +2—3 drops EBT
End Point: wine red to sky blue
Burette Burette reading: 'y' ml Calculation:
l) Standardization of EDTA: EDTA MgS04

MIVI M2V2
Il) Total Hardness of water:
Hardness of water = y x Z x 100 x 1000/ V ppm CaC03 equivalent (Note:
whole equation is multiplied by 1000 so as to convert in to ppm or mg/l)

*Alkalinity of water sample

Alkalinity is defined as the capacity of a water to neutralize an acid.
-A natural water may be alkaline due to presence of hydroxides, bicarbonates, and
carbonates compounds dissolved in water.
1)Hydroxides - NH40H,
2)Bicarbonates-
3) Carbonates- Mg C03 , Fe C03

Hydroxides, carbonates and bicarbonates estimated by titration against std acid HCI.
-In most natural and treated waters, alkalinity is imparted to the water by the carbonate
system.

Theory: Alkaline water Vs HCI

1) All OH- and 1/2 of C03-2 gets neutralized first , Indicated by phenolphthalein (P),
pink to colorless .pH of mixture decreases to about 8.7.

2) Remaining h of C03-2 (now present as HC03-) & complete HC03- (present in

sample water) is neutralized on further titration -Indicated by methyl orange (M),
yellow to orange at about pH 4.

Reaction :
OH + 1-120 ...(1) coe +
HC03- ...(2) HC03- +
1120 ...(3)
Types and Amount of alkalinities
a) only OH
b) only coe
c) only HC03-
d) Any two ions: OH- & C03-2
e) coe & HC03-,
OH- & HC03-do not co-exist. ,they react & form H20 + C03-2
HCOE + OH -5 1--120 + coe

Endpoint Alkalinity
OH - CO 3-2
 2P-M 2(M-P)

Procedure:
Part I: Phenolphthalein end point
10 ml of water sample + 1—2 drops phenolphthalein. All OH- and 1/2 of C03-2 gets
neutralized.
Solution in Burette: HCI solution.
Solution in pipette: 10 ml hard water
Indicator: 2—3 drops Phenolphthalein
Conical flask: Above 10 ml hard water+2—3 drops Phenolphthalein
End Point: pink to colorless
Burette Burette reading: 'VI' or P ml Part Il: Methyl Orange end point
Part I Solution + 2 drops of methyl orange indicator ,lf yellow solution, then continue to
titrate. If orange solution, then end pt is reached. End point indicates complete
neutralization of HC03-which are already present in water & which are produced due to
half neutralization of carbonates. End point of titration (part Il) = V2 or 'M'ml

Calculation:
1 ml IN acid solution = 50 mg of CaC03 equivalent
P Alkalinity
P Alkalinity: ppm of CaC03 equivalent
OR P Alkalinity = VI x Z X 50 1000/V of CaC03 equivalent
M Alkalinity
M Alkalinity: ppm of CaC03 equivalent
OR M Alkalinity = V2 x Z X 50 1000/V of CaC03 equivalent

*Ill effects of hard water in boiler

A) Caustic embrittlement
B) Boiler corrosion
C) Scale and sludge
D) Priming and foaming

A) Caustic embrittlement
Definition :
 • It is the fast corrosion of boiler caused by alkaline condition of water, during steam
generation, especially high-pressure steam boilers.
Phenomenon:

• Boiler material becomes brittle due to accumulation of caustic substances.

Caustic embrittlement Caused due to Factors
1) High tensile stress in the metal.
2) Leakages in the joints.
3) Presence of NaOH in boiler feed water.
Causes of Caustic embrittlement
Water softened by soda lime may contain unreacted quantity of Na2C03(caustic
soda).

Evaporation of water in boiler ,conc. of sodium carbonate(Na2C03) increase &

undergo hydrolysis to form sodium hydroxide (NaOH) at high temp.

Na2C03 + 2NaOH + C02

(Highly alkaline)

NaOH penetrates in minor cracks on inner surface of boiler by capillary action.

Boiler metal becomes weak & brittle due to caustic alkali.

Water evaporates as result ,caustic soda attacks the surrounding area , thereby
dissolving iron of boiler into sodium ferrite.

Fe + NaOH -> NaFe02+ H2

(sodium ferrite)

Disadvantages of Caustic embrittlement

1) Embittlement of bolier parts particularly at stressed parts like bends,joints
,rivets & may lead to failure of boiler.
2) Two types of cells are formed

i) Galvanic cells: stressed parts-anode ,Un-stressed parts —cathode i.e Anode gets
corroded
ii) Concentration cell: Higher conc. of NaOH in minor cracks stressed parts —anode ,
lower conc. of NaOH parts- cathode
Prevention of caustic embrittlement
1)Use of sodium phosphate instead of sodium carbonate.
2) Use of sodium sulphate.
3) Add tannin and lignin to fill crack. 4)Adjust the pH between
8-9 range.
B) Boiler corrosion
Corrosion of boiler takes place by chemical or electro chemical reaction.
i) Due to dissolved oxygen :
• Water usually contains about 8ml. of dissolved oxygen per litre at room temperature.
Dissolved oxygen in water in the presence of prevailing high temperature, attack the
boiler materials.
2Fe +21-120 + 02

4Fe(OH) +02 +2(Fe203 . 21-120)

Removal of oxygen /Prevention :
1. Adding calculated quantity of sulphite),hydrazine (N2H4) or
sodium sulphide (Na2S).
2. Mechanical de-aeration.
(ii) Due to dissolved carbon dioxide
The produced carbon dioxide reacts with water to give carbonic acid
C02 + 1-120 H2C03 which has

slow corrosive effect.

Removal of carbon dioxide /Prevention :

1. By adding NH3(ammonia).
2. Mechanical de-aeration.

(iii) Due to acids from dissolved salt/HydroIysis of salts

Water containing dissolved magnesium salts liberates acid on hydrolysis
CaC12 + 2H20 + 2HCl
MgC12 + 2H20 + 2HCl
MgS04 + 2H20 + H2S04
The liberated acid produces corrosion effect.

Removal Hydrolysis of salts/ Prevention :

1. By keeping pH value 8 to 9.
2. Boiler water should not contain salts of weak base -strong acid.
 C) Scale and sludge
Defn: Scale is hard & strong coating formed inside boiler tube & difficult to remove.
• It is bad conductor of heat.

Formation of Scale :
1)Decomposition of bicarbonate: At high temp. bicarbonate decompose into sticky water
insoluble material.

CaC03 + 1-120 + con

Mg (OH)2V + 1-120 +2C02T
2) Hydrolysis of Mg salt: At high temp
MgC12+2H20 -Y + 2HCl

3)Presence of Silica: Silica in the form of colloidal particles deposit as Ca ,Mg silicates.
4)Decreased solubility of CaS04: CaS04 lesser solubility (insoluble ) at high temp. CaS04 will
precipitate as hard scale.
Scale is composed of CaC03 , Mg (OH)2 , silica , CaS04 Solids fused together as coat.
DISADVANTAGES OF SCALES :
1 )WASTAGE OF FUEL: Scale is bad conductor of heat & reduction of heat transfer to the
boiler.
2)OVER HEATING OF BOILER: It reduce transfer of heat from boiler to boiler water ,need to
overheat the boiler.

3) BOILER SAFTEY DECREASES: Excess heating causes boiler metal to become soft &
weak. Reduce life of boiler & increase the maintenance of boiler.
4) DANGER OF EXPLOSION: Scale cracks due to uneven expansion ,the water comes
suddenly in contact with overheated boiler metal & causes large amount of steam formation
suddenly & sudden high pressure ,boiler metal may burst with explosion.
Removal of Scales

1. Use suitable chemicals (internal treatment) like EDTA, Sodium phosphate ,CaIgon
etc.

2. Use scraper or wire brush for thin scales .

3. By hammer & chisel
4. Thermal shocks technique.
5. By blow down operation.
Prevention of Scales

1. Use softened water.

2. Use scrapper hammer & chisel .
3. By adding organic chemicals like tannin,lignin
4. Adding sodium phosphate to water
5. Adding sodium aluminate ,which trap the scale forming particles.
Sludge
Defn: If ppt. is loose, soft & slimy & does not stick permanently to the boiler is called
sludge.

Formation :
It is normally formed where flow rate of water is lower than other part of
boiler.
Formed at cooler portions of boiler parts like edges, bends, valves, near
bending of pipe.
Disadvantages of sludge

1. Wastage of some heat .

2. May choke up the boiler pipe.
3. Reduce water flow rate in boiler
Prevention of sludge
1)Use of water containing very low total dissolved solids.
 2)Use of pretreated water.
3) By frequent blow down operation.

Comparison between sludge and scale

Sludge Scale
Loose slimy deposit. Hard coating.
Easily removed. Difficult to remove.
Formed at cooler part of boiler where flow Formed at hotter part of boiler.
rate is low.
Heat transfer is slightly affected. Heat transfer is greatly affected.
It leads to Choke the pipe. It leads to bulging or bursting or explosion
of pipe
Formed due to increase in salt Formed due to increase in concentration of
concentration silicates, Magnesium hydroxide, calcium
sulphate.

D) Priming and foaming

Priming : When the steam formation is rapid ,some water droplets are also carried along
with the steam. This ' wet steam' formation process is called priming
Causes of Priming 1.
Presence of excessive foam
2. Faulty boiler design
3. High speed of steam generation
4. High steam velocity

Disadvantages of Priming
1. Salt deposit on machine parts thereby decrease life of machinery.
2. It also causes corrosion.
Prevention
1. Use of softened & filtered water
2. Use steam purifier
3. Rapid changes in steam rate should be avoided
4. Maintain low water level.

Foaming: : Formation of continuous foam or bubbles on the surface of water. Priming &
foaming occur usually together
Causes of Foaming
1. High concentration of dissolved salts in boiler feed water
2. Presence of oil droplets & alkali
3. Presence of finely dispersed suspended materials
4. Violet agitation of boiler water.
 Disadvantages of Foaming
1. Difficult to maintain the constant pressure of steam in the presence of foaming.
2. Actual height of water level can't be judged well.
3. Foaming causes wet steam formation.
Prevention
1. Adding antifoaming agents like alcohol ,castor oil .
2. Use blow down operation.
3. Removing oil from water by adding sodium aluminate

1) Zeolite/Permutit method of water softening

Principle- sodium zeolite has the property of exchanging metal ions from water with
loosely held Na+ ions in zeolite
The chemical formula for permutit is Na20, A1203.xSi02 yH20. In short it is written as
Na2Z.

HARD "TER BRINE

(Naco SOLN.

WATER

GRAVELPERMUTITOR ZEOUTE

USTE WATER

PERMUTIT'S PROCESS OF SOFTENING

OF HARD WATER

Process-

1. Plant consists of steel tank containing a thick layer of sodium zeolite. The tank is also
the inlet for passing the brine.

2. Raw water is introduced through an inlet. When it passes through a layer of zeolite,
equilibrium is formed between sodium ions from zeolite & cations present in the
water, then cations from hard water taken by zeolite & eq. amount of Na ions are
released in exchange.
Reaction:
Ca-Z + 2Na+
 Mg-z +2Na+

Regeneration
When permutit is completely converted into calcium & magnesium permutit & it ceases
to soften the water. It gets exhausted. At this stage, the supply of hard water is stopped
& the exhausted permutit is regenerated by treating the bed with Conc. 10% NaCl
solution.
Ca-Z + 2NaCl Na2-Z + CaC12
Mg-z + 2NaCl Na2-Z + MgC12
Advantages

• Hardness can be completely removed

• 2. Easy operation. No experts required
• 3. Less time and sludge

• 4. Small area requires

Disadvantages

• Only Ca+ and Mg+ ions can be removed

• 2. Large amount of Na ions present in treated water.
• 3. Water should be free from suspended impurities to prevent clogging on Zeolite
beds.
2) Ion exchange/demineralization/Deionisation process
Principle: When water containing cations &anions ,is passed through the resins, cation
exchanger resin captures all cations(in exchange of H+) & anion exchanger resin captures all
anions((in exchange of OH-),to give pure & all ions free water.
A) cation exchanger resin -RH2
B) anion exchanger resin —R'(OH)2
IMPURE WATER WATER + ACID WATER + CO2

STEAM
JACKET
 GRAVEL
1
R 1
H2

CHANGER

R(OH

DEGASIFIER
FOR
REGENERATION
WASHINGS WASHINGS

ANION
ACID

DEMINERA
USED
WATER
ALKALI FOR
EXCHANGER REGENERATION

DEMINERAISATION PROCESS BY
'ON-EXCHANGE

Process

1. In the process two columns, one consist of cation exchange resin & another consist
of anion exchange resin are used.

2. The hard water is first allowed to pass through a column containing cation exchange
resins. Which remove all the cations like Ca+2, Mg+2 etc. and release H+ ion.

3. Reaction in first column takes place as under.

R-H2 + CaC12 Ca-R + 2HCl
R-H2 + CaS04 Ca-R -- H2S04
4. The anions like chloride & sulphates are converted into acid like HCI & H2S04. Which
is passed through another column containing anion exchanger i.e. R(OH)2 resin
where the following reaction takes place.

+ 2HCl R-C12 + 21-120

+ H2S04 R-S04 + 2H20
5. Water thus obtained is free from all cations and anions & is called soft water or distill
water.
Regeneration:

• When both resins get fully exhausted then they are regenerated. The cation resin is
regenerated by passing dilute acid solution (in first column). While anion resin is
regenerated by passing dilute NaOH solution (in second column), followed by
washing with water.
Ca-R + 2HCl -+ R-H2 + CaC12 (in first column)
R-C12 + 2NaOH + 2NaCl (in second column )
• The regenerated acidic and basic resins are again reused for softening of hard water.
Advantages

1. Water of zero hardness & no ionic impurities

2. Gaseous impurities like C02,02 expelled ,to get water of 'Distilled water standard'.
3. Equipment occupies small space.

4. Easy to operate.
5. Self adjusts with water of any hardness.
Limitations
1 . Initial high investment.
2.0nly for small scale purification of water

REVERSE OSMOSIS
Principle /Definition: The reversal of solvent flow, from higher concentration solution to
lower conc. solution through a semipermeable membrane ,by applying an external pressure
slightly higher than osmatic pressure of higher conc. solution ,is known as reverse osmosis

Reverse Osmosis
Applied Pressure Pure Water

Construction

1. In the RO, we applying an external pressure slightly higher than osmatic pressure of
higher conc. solution than osmatic pressure.
 2. The flow of solvent takes place in reverse direction.
Method
1. Sea water /polluted /ionic pollutants is filled in RO cell.
2. A pressure of 200psi is applied on it to force solvent to pass through SPM.
3. SPM has such porosity that it allows only small molecules of water.

4. Treated water comes out from the bottom outlet.

5. Thus, in RO we separate water from its contaminants rather than contaminants from
water .
Advantages

1. RO removes all ionic ,colloidal, non-ionic impurities from water.

2. Simple to operate
3. Low cost

4. SPM is specially prepared such that it allows limited quntuty of salts to pass thr.it along
with water .
5. RO technique is used to obtain drinking mineral water

Electrodialysis
Principle /Definition: Process of removing dissolved ionic impurities (salts, ionic dyes) from
water by using membrane & electric field, is known as electrodialysis

CONSTRUCTION

1. Electrodialysis cell consist of a large number of paired sets of plastic membranes

2. Membranes are ion selective i) Cation selective membrane will allow only cations to
pass through it , which repel anions & do not allow to go through.ii) Anion selective
 membrane will allow only anions to pass through it , which repel cations & do not
allow to go through.

3. When electric field applied ,the cations get attracted towards cathode electrode &
pass though cation selective membrane in the neighboring compartment.

4. Similarly ,anions get attracted towards anode electrode & pass though anion selective
membrane in the neighboring compartment.

5. Result will be alternate compartments with salts rich water and neighboring
compartment with pure water.
Applications

1. Removal of ionic pollutants (toxic salts , ionic dyes).

2. Removal of salts from sea water ,to get pure water.
3. Removal of limited quantity of salts from sea water to get drinking water.
4. Salts rich water used to recover salts.
Limitations
1. Does not remove dissolved organic matter.
2. Does not remove colloidal impurities.
3. Membrane replacement is costly

(Note : Numerical on Hardness, Alkalinity and Zeolite )

Numerical on Hardness
1) 25 ml of water sample required 8.8 ml of 0.01m EDTA to reach the end point.25ml of the
same water sample after boiling & filtration required 6.5 ml of same EDTA solution to reach
the end point. Calculate total &permanent hardness of the water sample.
V= Vol. of water sample titrated = 25 ml Z =
Molarity of EDTA solution = 0.01M y = vol. of
EDTA (Burette reading) = 8.8 ml

Step- I : Total Hardness y xzx 100 x 1000/ V ppm CaC03 eq.

= 8.8 x 0.01 x100 x 1000 / 25
= 352 ppm CaC03 eq.
Step- Il : Permanent Hardness (after boiling & filtration)
V= Vol. of water sample titrated = 25 ml
 Z = Molarity of EDTA solution = 0.01M y = vol. of EDTA
(Burette reading) = 6.5 ml y xzx 100 x 1000/ V ppm CaC03
eq.
= 6.5 x 0.01 x100 x 1000 / 25
260 ppm CaC03 eq.
Numerical on Zeolite
c) The hardness of water sample 50000 litres of water sample was removed by
passing it through a zeolite bed. The zeolite bed then required 200 liters of NaCl
solution containing 100g/liter of NaCl for regeneration. Calculate the hardness of
water sample.(3M)
- Given: Hard water = 50000 lit., Vol.of NaC1 solution = 200 lit., gm/lit of NaC1 IOOg/1it

Step-I mg of NaCl = gm/lit x vol. of NaC1 x 1000

100 x 200 x 1000
x 107 mg NaC1

Step-Il Quantity of NaCl in terms of CaC03 (y) mg NaC1 x

50/ 58.5 2 x 107 x 50/58.5
1.7094 x 107 mg CaC03 OR -
170940107.1 mg CaC03
Step-Ill Hardness
Hardness of water x Litre of water

Hardness of water y/ Litre of water

1.7094 x 107 /50000

= 341.88 ppm CaC03 eq