ENGINEERING CHEMISTRY 2021-2022
ARASU ENGINEERING COLLEGE
KUMBAKONAM – 612 501
DEPARTMENT OF CHEMISTRY
CY3151 – ENGINEERING CHEMISTRY
1
, ENGINEERING CHEMISTRY 2021-2022
UNIT-I: WATER AND ITS TREATMENT
PART-A
1. Define hardness.
Hardness is the property or characteristics of water, which does not produce lather with
soap.
2. List out the requirements of boiler feed water.
a) Boiler feed water should have zero hardness.
b) It must be free from dissolved gases like O2, CO2.
c) It should be free from suspended impurities.
d) It should be free from dissolved salts and alkalinity.
e) It should be free from oil and turbidity.
f) It should be free from total dissolved solids.
3. What are the salts responsible for carbonate and non-carbonate hardness of water?
Carbonate hardness: Ca(HCO3)2 and Mg(HCO3)2.
Non-Carbonate hardness: CaCl2, CaSO4, MgCl2, MgSO4.
4. Define softening of water. How is it carried out?
The process of removing hardness producing salts from water is known as softening or
conditioning of water.
Softening of water can be done in two methods.
i. External treatment ii. Internal treatment
5. What are boiler compounds? Mention two different boiler compounds and their
actions.
Scale forming substances can be removed by adding chemicals directly to the boiler. These
chemicals are called boiler compounds.
Example: Sodium carbonate and sodium phosphate.
6. Distinguish between internal and external conditioning of water.
Internal treatment External treatment
It is carried out within the boiler It is carried out before feeding the water into the boiler
It is used for low pressure boilers It is used for high pressure boilers
It requires blow down operation Blow down operation is not required
It is cheap. It is expensive
Chemicals are used. No chemicals are used
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, ENGINEERING CHEMISTRY 2021-2022
7. Why calgon conditioning is better than phosphate conditioning?
Calgon forms highly soluble complex with hardness producing salts and no sludge
formation. But in phosphate conditioning, it gives sludge and it is required to dispose
periodically. Hence, calgon conditioning is better than phosphate conditioning.
8. Define desalination.
The process of removing common salt (sodium chloride) from the water is known as
desalination. This can be done by Reverse Osmosis process.
9. How is hardness of water expressed (Or) Bring out the significance of calcium
carbonate equivalents?
The concentration of hardness producing salts is usually expressed in terms of an
equivalent amount of CaCO3.
Significance: Molecular weight of CaCO3 is a whole number and it is the most insoluble
salt. If the concentration of hardness producing salt is x mg/lit, then
x × Molecular weight of CaCO3
Amount of Hardness
equivalent to CaCO3 =
Molecular weight of hardness producing substance
10. What are the disadvantages of scale formation? (Or) Mention any two disadvantages
of formation of deposits in steam boilers.
Scales act as thermal insulators. It decreases the efficiency of boiler. Any crack developed
on the scale, leads to explosion of the boilers.
11. What is meant by caustic embrittlement? How is it prevented.
Caustic embrittlement means intercrystalline cracking of boiler metal by sodium
hydroxide (NaOH, caustic).
Prevention:
a) Using sodium phosphate as softening agent instead of sodium carbonate.
b) By adding tannin, lignin to the boiler water, which blocks the hair cracks.
12. Soft water is not demineralised (DM) water whereas DM water is soft water. Justify.
The soft water produced by lime-soda and zeolite process, does not contain any hardness
producing Ca2+ and Mg2+ ions, but it will contain other ions like Na+, K+, SO42-, Cl- etc.
On the other hand demineralised water does not contain both anions and cations of
dissolved salts.
3
ARASU ENGINEERING COLLEGE
KUMBAKONAM – 612 501
DEPARTMENT OF CHEMISTRY
CY3151 – ENGINEERING CHEMISTRY
1
, ENGINEERING CHEMISTRY 2021-2022
UNIT-I: WATER AND ITS TREATMENT
PART-A
1. Define hardness.
Hardness is the property or characteristics of water, which does not produce lather with
soap.
2. List out the requirements of boiler feed water.
a) Boiler feed water should have zero hardness.
b) It must be free from dissolved gases like O2, CO2.
c) It should be free from suspended impurities.
d) It should be free from dissolved salts and alkalinity.
e) It should be free from oil and turbidity.
f) It should be free from total dissolved solids.
3. What are the salts responsible for carbonate and non-carbonate hardness of water?
Carbonate hardness: Ca(HCO3)2 and Mg(HCO3)2.
Non-Carbonate hardness: CaCl2, CaSO4, MgCl2, MgSO4.
4. Define softening of water. How is it carried out?
The process of removing hardness producing salts from water is known as softening or
conditioning of water.
Softening of water can be done in two methods.
i. External treatment ii. Internal treatment
5. What are boiler compounds? Mention two different boiler compounds and their
actions.
Scale forming substances can be removed by adding chemicals directly to the boiler. These
chemicals are called boiler compounds.
Example: Sodium carbonate and sodium phosphate.
6. Distinguish between internal and external conditioning of water.
Internal treatment External treatment
It is carried out within the boiler It is carried out before feeding the water into the boiler
It is used for low pressure boilers It is used for high pressure boilers
It requires blow down operation Blow down operation is not required
It is cheap. It is expensive
Chemicals are used. No chemicals are used
2
, ENGINEERING CHEMISTRY 2021-2022
7. Why calgon conditioning is better than phosphate conditioning?
Calgon forms highly soluble complex with hardness producing salts and no sludge
formation. But in phosphate conditioning, it gives sludge and it is required to dispose
periodically. Hence, calgon conditioning is better than phosphate conditioning.
8. Define desalination.
The process of removing common salt (sodium chloride) from the water is known as
desalination. This can be done by Reverse Osmosis process.
9. How is hardness of water expressed (Or) Bring out the significance of calcium
carbonate equivalents?
The concentration of hardness producing salts is usually expressed in terms of an
equivalent amount of CaCO3.
Significance: Molecular weight of CaCO3 is a whole number and it is the most insoluble
salt. If the concentration of hardness producing salt is x mg/lit, then
x × Molecular weight of CaCO3
Amount of Hardness
equivalent to CaCO3 =
Molecular weight of hardness producing substance
10. What are the disadvantages of scale formation? (Or) Mention any two disadvantages
of formation of deposits in steam boilers.
Scales act as thermal insulators. It decreases the efficiency of boiler. Any crack developed
on the scale, leads to explosion of the boilers.
11. What is meant by caustic embrittlement? How is it prevented.
Caustic embrittlement means intercrystalline cracking of boiler metal by sodium
hydroxide (NaOH, caustic).
Prevention:
a) Using sodium phosphate as softening agent instead of sodium carbonate.
b) By adding tannin, lignin to the boiler water, which blocks the hair cracks.
12. Soft water is not demineralised (DM) water whereas DM water is soft water. Justify.
The soft water produced by lime-soda and zeolite process, does not contain any hardness
producing Ca2+ and Mg2+ ions, but it will contain other ions like Na+, K+, SO42-, Cl- etc.
On the other hand demineralised water does not contain both anions and cations of
dissolved salts.
3
