UNIT I - WATER TECHNOLOGY
PART - A
1. Define hard water and soft water.
Hard water does not produce lather with soap solution readily, but forms a white precipitate. Hardness
is due to presence of Ca and Mg salts.
Soft water readily gives lather with soap solution. It does not contain dissolved calcium and
magnesium salts.
2. How is hardness of water detected?
Hardness can be detected by
i). Hard water does not produce lather with soap solution.It forms white precipitate.,
2C17H35COONa +CaCl2 (C17H35COO)2 Ca + 2 NaCl
(Soap) (Hardness producing salt) White Precipitate
ii). it produces wine red colour with Eriochrome Black-T indicator at pH 9-10
3. Explain temporary and permanent hardness of water.
Temporary hardness: It is due to presence of bicarbonates of Ca and Mg. It can be removed by i)
boiling the water ii) adding lime to the water
Ca (HCO3)2 CaCO3 ↓ + H2O+ CO2 ↑
Permanent hardness: It is due to presence of chlorides and sulphates of Ca and Mg.It can be removed
by i) sodalime process and ii) Zeolite process
CaCl2 + Na2CO3 CaCO3 ↓ + 2NaCl
4. Why CaCO3 is used as standard for expressing hardness? Give the units of hardness.
CaCO3 is used as standard for expressing hardness because,
(i) It is the most insoluble salt
(ii) Its molecular weight is 100, Equivalent weight is 50, and therefore calculation is simple
Amt. of Hardness producing salt is × 100 (Mol. Wt of CaCO 3)
Amount equivalent of CaCO3 =
Mol. Wt of Hardness producing salt
Units of hardness: a) Parts per million (ppm) b) Milligram per litre (mg/Lit)
5. Sample water contains 16.8 mgs of MgCO3 and 8.1 mgs of Ca(HCO3)2. Calculate the hardness in
terms of CaCO3 equivalent.
Solution:
Amt. of Hardness producing salt is × 100 (Mol. Wt of CaCO 3)
Amount equivalent of CaCO3 =
Mol. Wt of Hardness producing salt
Name of the salt Amount in mg/Lit Mol. Wt of given Amt. Equivalent
producing hardness (Given Data) salt of CaCO3
16.8 × 100
MgCO3 16.8 84 84
= 20 mg/Lit
8.1 × 100
Ca(HCO3)2 8.1 162 162
= 20 mg/Lit
,6. Draw the structure of EDTA and basic reaction (principle) of EDTA method.
Structure of Ethylene Diamine Tetra Acetic acid (EDTA):
HOOCH2C CH2COOH
N – CH2 – CH2 – N
HOOCH2C CH2COOH
Reaction (Principle) of EDTA method:
Ca2+ PH = 8–10 Ca PH = 8–10
+ EBT EBT + EDTA
Mg2+ (Eriochrome Black-T) Mg
(Weak complex)
Wine red colour
Ca
EDTA + EBT
Mg Steel blue
(Stable complex)
7. Mention the units used for expressing hardness of water.
Parts per million (ppm), or milligram per litre (mg/L).
8.What are the requirements of boiler feed water?
The water fed into the boiler for the production of steam is known as boiler feed water
It should be free from (i). Suspended solids. (ii). Dissolved salts like MgCl 2 (iii). Hardness. (iv). Alkalinity.
(v). Dissolved gases like O2 and CO2
Hardness-<0.2ppm,Soda alkalinity-0.15-1ppm,Caustic alkalinity-0.15-0.45ppm,Excess soda ash-0.3-
0.55ppm,Dissolved gases like O2,CO2-0 ppm
9. What are the disadvantages using hard water in boiler or what are boiler troubles?
1. Scale and sludge formation. 2. Caustic Embrittlement. 3. Priming and Foaming. 4. Boiler
corrosion
10. Define scale and sludge formation in boilers.
Sludge is a soft, loose, slimy precipitate formed inside the boiler. (It is formed by substances like
MgCl2, MgCO3 and CaCl2 )
Scale is a hard, adherent deposit formed on the inner surface of the boiler. (It is formed by substances
like Mg(OH)2, Ca(HCO3)2and CaSO4)
11. What is blow-down operation?
Blow-down operation is a process of removing a portion of concentrated water by fresh water frequently
from the boiler during steam production
12. What are boiler compounds?
The chemicals directly added into the boiler for removing scale forming substances is known as boiler
compounds. Ex: Sodium carbonate,Sodium phosphate, Sodium hexa meta phosphate and colloidal
conditioning.
13. Distinguish between internal conditioning and external conditioning methods.
Internal conditioning External conditioning
Treating the boiler water after feeding it into Treating the boiler water before feeding it into boiler
boiler by adding chemicals to remove scale is called external conditioning.
forming substance is called internal conditioning
Ex: carbonate conditioning, phosphate
conditioning, calgon conditioning Ex: zeolite process, Demineralisation process
,14. Distinguish between soft water and demineralised water or Demineralised water is soft water but
Soft water is not Demineralised water. Why?
The soft water (produced by Lime soda and zeolite processes) does not contain hardness producing Ca 2+
and Mg2+ ions but it will contain other ions like Na+ ,K+ , So42- ,Cl- etc..,
Demineralised water does not contain both anions and cations
15. How is phosphate conditioning carried out?
The formation of scale is prevented by adding sodium phosphate (Na 3PO4) The added phosphate reacts
with calcium and magnesium salts forming soft sludge.
3 CaCl2+2 Na3PO4 Ca3 (PO4)2 +6 NaCl
This process is suitable for high pressure boilers.
16. Explain the chemical reaction involved in Calgon conditioning. AU-2014
This process involves the addition of sodium hexa meta phosphate in boiler water. It prevents scales
and sludge formation by forming soluble complex.
CaSO4 + Na2[Na4(PO3)6 ] Na2[Ca2(PO3)6 ]+ 2 Na2SO4
Soluble complex
17. How is Sodium aluminate conditioning carried out
It is formation of sludge by adding of sodium aluminate, the sludge is removed by blow down
operation.
NaAlO2+ 2H2O NaOH + Al(OH)3
Sodium aluminate reacts with boiler water (hydrolysis) to produce Sodium hydroxide and aluminium
hydroxide
MgCl2+ 2NaOH 2NaCl+Mg(OH)2
Sodium hydroxide reacts with magnesium chloride to produce magnesium hydroxide
The flocculent precipitate of Al(OH)3 and Mg(OH)2 produced inside the boiler are finely suspended
and colloidal impurities including oil drops and silica
18. What is desalination?
The process of removing common salt (NaCl) from the water (salt water or brackish water) is known as
desalination. It can be carried out by Reverse osmosis (RO) process
19. What is Reverse osmosis?
When two solutions of different concentrations are separated by a semipermeable membrane, If pressure
in excess of osmotic pressure is applied on the higher concentrated side, the solvent flow from higher
concentration to lower concentration side. This process is called reverse osmosis
20. What are the advantages of reverse osmosis method and limitations?
i. Low capital cost, easy operating.
ii. RO method is used for converting sea water into drinking water.
iii. It removes all types of impurities like non-ionic and colloidal.
iv. The life time of membrane is high and it can be replaced within few minutes
Limitations
1. The water is demineralized. Since most mineral particles (including sodium, calcium, magnesium,
magnesium, and iron
2. High Hydrostatic pressure should be need for this process.
21. Distinguish between internal conditioning and external conditioning methods of water.
Internal Treatment External Treatment
It is carried out before feeding into the boiler It is carried out within the boiler
It is used for high pressure It is used for Low pressure boiler
Blow down operation is not required Blow down operation is required
, 22. Distinguish between carbonate (Temporary hardness) CH and noncarbonated hardeness
(permanent) NCH
Carbonate (Temporary hardness)CH Non-carbonate hardness (Permanent) NCH
It is due to bicarbonate of calcium and magnesium It is due to chloride and sulphate of calcium
magnesium
It can be removed by boiling the water It can not be removed by boiling the water
It is also called as alkaline It is also called as Non-alkaline
Example: Ca(HCO3)2 Mg(HCO3)2 Example: CaCl2,CaSO4
23. What is mean by internal conditioning of water?
Internal conditioning is the processes which involve the removal of scale forming substance by
adding chemicals directly in to the boiler.
24. Why calgon conditioning is better than the phosphate conditioning .
In Calgon conditioning calgon forms highly soluble complex but in phosphate conditioning it give
sludge, So periodical disposal of sludge is important in phosphate conditioning but calgon conditioning no
problem of disposal
PART– B
16 Marks Questions
1. Explain the estimation of hardness by EDTA method
2. What are the troubles caused by using hard water in boilers? or (Disadvantages of using hard water
in boilers)How it can be prevented? (16).
3. Define external conditioning and explain the demineralization of water by ion-exchange process.
How exhausted cation and anion exchange resins are regenerated? (10)
4. Describe zeolite process for water treatment.(6)
5. Explain internal conditioning of boiler feed water (8)
6. What is desalination? With a neat diagram describe reverse osmosis in detail.
1. Explain the estimation of hardness by EDTA method. (8)
EDTA is Ethylene Diamine Tetra Acetic acid. The structure of EDTA is
Since, EDTA is insoluble in water; its disodium salt is used as a sequestering or complexing agent.
Principle:
1) The amount of hardness causing ions (Ca2+ and Mg2+) can be estimated by titrating the water sample
against EDTA.
2) Indicator –Eriochrome Black-T (EBT).
3) Buffer solution - a mixture of NH4Cl – NH4OH is added to maintain the PH at 8-10.
PART - A
1. Define hard water and soft water.
Hard water does not produce lather with soap solution readily, but forms a white precipitate. Hardness
is due to presence of Ca and Mg salts.
Soft water readily gives lather with soap solution. It does not contain dissolved calcium and
magnesium salts.
2. How is hardness of water detected?
Hardness can be detected by
i). Hard water does not produce lather with soap solution.It forms white precipitate.,
2C17H35COONa +CaCl2 (C17H35COO)2 Ca + 2 NaCl
(Soap) (Hardness producing salt) White Precipitate
ii). it produces wine red colour with Eriochrome Black-T indicator at pH 9-10
3. Explain temporary and permanent hardness of water.
Temporary hardness: It is due to presence of bicarbonates of Ca and Mg. It can be removed by i)
boiling the water ii) adding lime to the water
Ca (HCO3)2 CaCO3 ↓ + H2O+ CO2 ↑
Permanent hardness: It is due to presence of chlorides and sulphates of Ca and Mg.It can be removed
by i) sodalime process and ii) Zeolite process
CaCl2 + Na2CO3 CaCO3 ↓ + 2NaCl
4. Why CaCO3 is used as standard for expressing hardness? Give the units of hardness.
CaCO3 is used as standard for expressing hardness because,
(i) It is the most insoluble salt
(ii) Its molecular weight is 100, Equivalent weight is 50, and therefore calculation is simple
Amt. of Hardness producing salt is × 100 (Mol. Wt of CaCO 3)
Amount equivalent of CaCO3 =
Mol. Wt of Hardness producing salt
Units of hardness: a) Parts per million (ppm) b) Milligram per litre (mg/Lit)
5. Sample water contains 16.8 mgs of MgCO3 and 8.1 mgs of Ca(HCO3)2. Calculate the hardness in
terms of CaCO3 equivalent.
Solution:
Amt. of Hardness producing salt is × 100 (Mol. Wt of CaCO 3)
Amount equivalent of CaCO3 =
Mol. Wt of Hardness producing salt
Name of the salt Amount in mg/Lit Mol. Wt of given Amt. Equivalent
producing hardness (Given Data) salt of CaCO3
16.8 × 100
MgCO3 16.8 84 84
= 20 mg/Lit
8.1 × 100
Ca(HCO3)2 8.1 162 162
= 20 mg/Lit
,6. Draw the structure of EDTA and basic reaction (principle) of EDTA method.
Structure of Ethylene Diamine Tetra Acetic acid (EDTA):
HOOCH2C CH2COOH
N – CH2 – CH2 – N
HOOCH2C CH2COOH
Reaction (Principle) of EDTA method:
Ca2+ PH = 8–10 Ca PH = 8–10
+ EBT EBT + EDTA
Mg2+ (Eriochrome Black-T) Mg
(Weak complex)
Wine red colour
Ca
EDTA + EBT
Mg Steel blue
(Stable complex)
7. Mention the units used for expressing hardness of water.
Parts per million (ppm), or milligram per litre (mg/L).
8.What are the requirements of boiler feed water?
The water fed into the boiler for the production of steam is known as boiler feed water
It should be free from (i). Suspended solids. (ii). Dissolved salts like MgCl 2 (iii). Hardness. (iv). Alkalinity.
(v). Dissolved gases like O2 and CO2
Hardness-<0.2ppm,Soda alkalinity-0.15-1ppm,Caustic alkalinity-0.15-0.45ppm,Excess soda ash-0.3-
0.55ppm,Dissolved gases like O2,CO2-0 ppm
9. What are the disadvantages using hard water in boiler or what are boiler troubles?
1. Scale and sludge formation. 2. Caustic Embrittlement. 3. Priming and Foaming. 4. Boiler
corrosion
10. Define scale and sludge formation in boilers.
Sludge is a soft, loose, slimy precipitate formed inside the boiler. (It is formed by substances like
MgCl2, MgCO3 and CaCl2 )
Scale is a hard, adherent deposit formed on the inner surface of the boiler. (It is formed by substances
like Mg(OH)2, Ca(HCO3)2and CaSO4)
11. What is blow-down operation?
Blow-down operation is a process of removing a portion of concentrated water by fresh water frequently
from the boiler during steam production
12. What are boiler compounds?
The chemicals directly added into the boiler for removing scale forming substances is known as boiler
compounds. Ex: Sodium carbonate,Sodium phosphate, Sodium hexa meta phosphate and colloidal
conditioning.
13. Distinguish between internal conditioning and external conditioning methods.
Internal conditioning External conditioning
Treating the boiler water after feeding it into Treating the boiler water before feeding it into boiler
boiler by adding chemicals to remove scale is called external conditioning.
forming substance is called internal conditioning
Ex: carbonate conditioning, phosphate
conditioning, calgon conditioning Ex: zeolite process, Demineralisation process
,14. Distinguish between soft water and demineralised water or Demineralised water is soft water but
Soft water is not Demineralised water. Why?
The soft water (produced by Lime soda and zeolite processes) does not contain hardness producing Ca 2+
and Mg2+ ions but it will contain other ions like Na+ ,K+ , So42- ,Cl- etc..,
Demineralised water does not contain both anions and cations
15. How is phosphate conditioning carried out?
The formation of scale is prevented by adding sodium phosphate (Na 3PO4) The added phosphate reacts
with calcium and magnesium salts forming soft sludge.
3 CaCl2+2 Na3PO4 Ca3 (PO4)2 +6 NaCl
This process is suitable for high pressure boilers.
16. Explain the chemical reaction involved in Calgon conditioning. AU-2014
This process involves the addition of sodium hexa meta phosphate in boiler water. It prevents scales
and sludge formation by forming soluble complex.
CaSO4 + Na2[Na4(PO3)6 ] Na2[Ca2(PO3)6 ]+ 2 Na2SO4
Soluble complex
17. How is Sodium aluminate conditioning carried out
It is formation of sludge by adding of sodium aluminate, the sludge is removed by blow down
operation.
NaAlO2+ 2H2O NaOH + Al(OH)3
Sodium aluminate reacts with boiler water (hydrolysis) to produce Sodium hydroxide and aluminium
hydroxide
MgCl2+ 2NaOH 2NaCl+Mg(OH)2
Sodium hydroxide reacts with magnesium chloride to produce magnesium hydroxide
The flocculent precipitate of Al(OH)3 and Mg(OH)2 produced inside the boiler are finely suspended
and colloidal impurities including oil drops and silica
18. What is desalination?
The process of removing common salt (NaCl) from the water (salt water or brackish water) is known as
desalination. It can be carried out by Reverse osmosis (RO) process
19. What is Reverse osmosis?
When two solutions of different concentrations are separated by a semipermeable membrane, If pressure
in excess of osmotic pressure is applied on the higher concentrated side, the solvent flow from higher
concentration to lower concentration side. This process is called reverse osmosis
20. What are the advantages of reverse osmosis method and limitations?
i. Low capital cost, easy operating.
ii. RO method is used for converting sea water into drinking water.
iii. It removes all types of impurities like non-ionic and colloidal.
iv. The life time of membrane is high and it can be replaced within few minutes
Limitations
1. The water is demineralized. Since most mineral particles (including sodium, calcium, magnesium,
magnesium, and iron
2. High Hydrostatic pressure should be need for this process.
21. Distinguish between internal conditioning and external conditioning methods of water.
Internal Treatment External Treatment
It is carried out before feeding into the boiler It is carried out within the boiler
It is used for high pressure It is used for Low pressure boiler
Blow down operation is not required Blow down operation is required
, 22. Distinguish between carbonate (Temporary hardness) CH and noncarbonated hardeness
(permanent) NCH
Carbonate (Temporary hardness)CH Non-carbonate hardness (Permanent) NCH
It is due to bicarbonate of calcium and magnesium It is due to chloride and sulphate of calcium
magnesium
It can be removed by boiling the water It can not be removed by boiling the water
It is also called as alkaline It is also called as Non-alkaline
Example: Ca(HCO3)2 Mg(HCO3)2 Example: CaCl2,CaSO4
23. What is mean by internal conditioning of water?
Internal conditioning is the processes which involve the removal of scale forming substance by
adding chemicals directly in to the boiler.
24. Why calgon conditioning is better than the phosphate conditioning .
In Calgon conditioning calgon forms highly soluble complex but in phosphate conditioning it give
sludge, So periodical disposal of sludge is important in phosphate conditioning but calgon conditioning no
problem of disposal
PART– B
16 Marks Questions
1. Explain the estimation of hardness by EDTA method
2. What are the troubles caused by using hard water in boilers? or (Disadvantages of using hard water
in boilers)How it can be prevented? (16).
3. Define external conditioning and explain the demineralization of water by ion-exchange process.
How exhausted cation and anion exchange resins are regenerated? (10)
4. Describe zeolite process for water treatment.(6)
5. Explain internal conditioning of boiler feed water (8)
6. What is desalination? With a neat diagram describe reverse osmosis in detail.
1. Explain the estimation of hardness by EDTA method. (8)
EDTA is Ethylene Diamine Tetra Acetic acid. The structure of EDTA is
Since, EDTA is insoluble in water; its disodium salt is used as a sequestering or complexing agent.
Principle:
1) The amount of hardness causing ions (Ca2+ and Mg2+) can be estimated by titrating the water sample
against EDTA.
2) Indicator –Eriochrome Black-T (EBT).
3) Buffer solution - a mixture of NH4Cl – NH4OH is added to maintain the PH at 8-10.
