Types of water, impurities present in water, Hardness of water, water softening method .

1. WATER

2. •Definition of Hardness: It is capacity of water to form
lather with soap. Or
It is defined as the soap consuming capacity of a water
sample.
Hardness of Water
•Types of Hardness: There are two types of Hardness:
A) Temporary Hardness (Carbonate Hardness): It is due to presence
of carbonate ions of calcium and magnesium. It can be removed by
boiling.
B) Permanent Hardness (Non-carbonate Hardness): It is due to
presence of sulphates and chlorides of calcium and magnesium. It
can not be removed by boiling.

3. Note: 1) Formula of Salts: e.g. Nitrates and Sulphates
salts
e.g. MNO3 if M= Monovalent metals like Na, K etc
M2SO4 if M= Monovalent metals like Na, K etc
M(NO3)2 if M= Divalent metals like Ca, Mg etc
MSO4 if M= Divalent metals like Ca, Mg etc
2) Following salts (salts of Na & K) does not contribute to
Hardness;
NaCl, KCl, NaNO3, KNO3, Na2SO4, K2SO4, Soda ash
(Na2CO3) etc.
3) Calculate Molecular Weight:
(Atomic Masses; H=1, C=12, N=14, O=16, Na=23,
Mg=24, Ca=40, Cl=35.5, S=32)
Numerical Problems on Water
(Compulsory 8Marks)

9. •Definition: Alkalinity of water is defined as tendency of water to
neutralize acid. It can be due to presence of ions like OH-, HCO3
-,
CO3
- - etc. The total alkalinity (A) is sum of hydroxide, carbonate and
bicarbonate alkalinity.
•Types: Alkalinity of water is classified in three types:
1) Hydroxide Alkalinity : Due to Hydroxyl ion denoted by OH-
2) Carbonate Alkalinity : Due to carbonate ion denoted by CO3
- -
3) Bicarbonate Alkalinity : Due to bi-carbonate ion denoted by HCO3
-.
•Causes: The alkalinity of natural water is due to the presence of salts of
weak acid and strong bases. The normal forms of alkalinity are
hydroxides (OH-), carbonates (CO3
--), and bicarbonates (HCO3
-). Natural
water also contains an appreciable amount of hydroxides and carbonate
alkalinity, particularly in surface water blooming with algae. The algae
take up carbon dioxide for photosynthesis and raise the pH of water.
Alkalinity of water

10. •The alkalinity of water is mainly due to hydroxides, carbonates and
bicarbonates.
•The disadvantages of Alkalinity are
I)Carbonate and Bicarbonate causes temporary hardness.
II)Alkaline water is also not suitable for domestic and industrial use.
III)Alkaline water helps scale and sludge formation in boilers.
IV)Alkaline water causes digestive disorder.
V)OH- alkalinity causes caustic embitterment of metallic component,
spares, machines, and equipments etc.
VI)Highly alkaline water may leads to caustic embrittlement and
deposition of precipitates and sludge in boiler and pipes.
VII)Alkalinity of water causes damage to water construction like
Bridge
VIII)Continuous use of alkaline water for agriculture spoils the soil
by change in pH.
•Hence, it is essential to have an idea about the nature and extent of
alkalinity. Therefore, the experimental procedure is aimed at
determination of alkalinity of the water sample.

15. SCALES & SLUDGES
SCALES
SLUDGES

16. SCALES

19. Sludges Scales
1 Sludges are soft, loose
and slimy precipitate.
Scales are hard deposits.
2 They are non-adherent
deposits and can be easily
removed.
They stick very firmly to the inner
surface of boiler and are very
difficult to remove.
3 Formedby substances
likeCaCl2, MgCl2, MgSO4,
MgCO3 etc.
Formed by substance like CaSO4,
Mg(OH)2 etc.
4 Formed at comparatively
colder portions of the
boiler.
Formed generally at heated
portions of the boiler.
5 They decrease the
efficiency of boiler but are
less dangerous.
Decrease the efficiency of boiler
and chances of explosions are also
there.
6 Can be removed by
blow-down operation.
Cannot be removed by blow-down
operation.

20. Priming and Foaming:
A) Priming: When steam is produced rapidly in the boilers,
some droplets of the liquid water are carried along-with the
steam. This process of "wet-steam' formation, is called
priming.
Priming is caused by :
•Presence of dissolved solids.
•High steam velocities
•Sudden boiling.
•Faulty design of boiler.
Priming can be avoided by:
•controlling rapid change in steaming velocities,
•the proper design of boilers (maintaining low water levels
in boilers),
•ensuring efficient softening and
•Filtration of the boiler-water carried over to the boiler.
•By blowing off sludge or scales from time to time.

21. B) Foaming: Production of persistent
foam or bubbles in boiler which do not
break easily is called foaming.
Foaming is caused by presence of
substance like oils.
Foaming can be avoided by addition of
anti-foaming agents, like sodium aluminate
and aluminium sulphate.

22. Boiler Corrosion:
Disadvantages:
Reasons:
1) Dissolved oxygen.
2) Mineral acids.
PREVENTION-By mechanical deaeration.

23. Reverse Osmosis (R.O.): The flow of solvent
from a solution of high concentration (i.e.
dilute solution) to low concentration
compartment through a semi-permeable
membrane, is called as Reverse Osmosis
(R.O.).
The reverse osmosis water treatment method has been
used extensively; (1mark)
•to obtain soft water c) to convert seawater
to drinking water,
•to clean up wastewater, and d) to recover
dissolved salts from industrial processes.

24. Osmosis Vs R.O. :
The flow of solvent from a solution of low concentration (i.e. dilute
solution) to high concentration compartment through a semi-
permeable membrane is called as Osmosis.
It is natural tendency where flow continues till the concentration
is equal on both the sides.

25. Reverse Osmosis (R.O.) Fig. (1mark)
OSMOTIC PRESSURE: The pressure created by the phenomenon of
osmosis, is called as ‘osmotic pressure’. OR The external pressure applied
to stop the phenomenon of osmosis is called as ‘osmotic pressure’.
If a pressure greater than osmotic pressure is applied on the compartment
having concentrated solution, the flow of solvent is reversed.
i.e. solvent is forced to move from concentrated solution to dilute
solution through the membrane. This is called as reverse osmosis.

26. Semi-Permeable Membrane (SPM) is
selective membrane which does not permit
the passage / flow of dissolved solute
particles. e.g. Cellophane, Thin films of
cellulose acetate, polymethyl acrylate and
polyamide polymers etc.

28. Advantages: (1mark)
1) RO removes many inorganic impurities from
drinking water.
2) Reverse osmosis treatment reduces the
concentration of dissolved solids, including a
variety of ions and metals and very fine
suspended particles.
3)RO also removes certain organic contaminants,
some detergents, and specific pesticides.
4)Colloidal SiO2 can be removed by reverse
osmosis which even cannot be removed by
demineralization.

29. Disadvantages / Limitations/ Drawbacks:
(1mark)
1)RO is not effective for removing
dissolved gases, some pesticides and
solvents, hydrogen sulfide gas,
chloramines etc.
2) The performance of an RO system depends
on membrane type, flow control, feed water
quality (e.g., turbidity, TDS, and pH),
temperature, and pressure.

30. Reverse Osmosis
• By overcoming the osmotic pressure, a
semipermeable membrane can be used to
purify water
30

31. Reverse Osmosis

32. Osmotic Pressure
The normal flow of solvent into the
solution (osmosis) can be prevented by
applying an external pressure to the
solution.
Osmotic Pressure useful for
 Determining the Molar Mass of
protein and other macromolecules
 small concentrations cause
large osmotic pressures
 Can prevent transfer of all solute
particles
 Dialysis at the wall of most
plant and animal cells

33. Ion Exchange Process:
(DEMINERALIZATION OF WATER)
Basic Principle:
(i) Cation exchange resins (R -H+)
(ii) Anion exchange resins (R +OH-)
Examples: Ambertite-400 Dowex-3
Examples: Ambertite-120

34. Ion Exchange Process:
(DEMINERALIZATION OF WATER)

35. Ion Exchange Process:
(DEMINERALIZATION OF WATER)

36. Ion Exchange Process:
(DEMINERALIZATION OF WATER)
H+
Mn+
An-
OH
-
Wate
r

38. Advantages
•The process can be used to soften highly acidic or alkaline waters.
•It produces water of very low hardness (say 2 ppm). So, the treated
water is very good for use in high pressure boilers.
Disadvantages
•Capital cost is high since chemical and equipment both are costly.
•If water contains turbidity then the efficiency of the process is reduced.

40. Other References

41. Colligative Properties
Osmosis
The net movement of solvent through a semi-permeable
membrane from a dilute to a concentrated solution.

42. III. Colligative Properties C. Osmosis
- Osmosis is the net flow of solvent molecules from a
pure solvent through a semipermeable membrane
into a solution.
- Osmotic Pressure (π) is a colligative property &
equals the pressure that, when applied to the
solution, just stops osmosis.

43. Osmotic Pressure
• Osmotic pressures can be very large.
– For example, a 1 M sugar solution has an osmotic
pressure of 22.4 atm or 330 p.s.i.
• Since this is a large effect, the osmotic pressure
measurements can be used to determine the
molar masses of very large molecules such as:
1. Polymers
2. Biomolecules like
• proteins
• ribonucleotides

44. 44
Osmotic Pressure
• When a solution and the pure solvent used in making that solution are placed on
either side of a semipermeable membrane, more solvent molecules flow out of
the pure solvent side of the membrane than solvent flows into the pure solvent
from the solution side of the membrane.
• That flow of solvent from the pure solvent side makes the volume of the solution
rise.
• When the height difference between the two sides becomes large enough, the net
flow through the membrane ceases due to the extra pressure exerted by the
excess height of the solution chamber.
• Converting that height of solvent into units of pressure gives a measure of the
osmotic pressure exerted on the solution by the pure solvent.
P = rgh
– P stands for pressure, r is the density of the solution, and h is the height of the solution.

45. 45
Setup for Measuring the Osmotic Pressure of a Solution

46. Osmosis
Osmosis is the net flow of a solvent through a
semipermeable membrane, from pure
solvent into a solution or from a solution of
a lower concentration into one of a higher
concentration.
A semipermeable membrane only lets the
solvent molecules through
46

47. Osmosis
47

48. Semi permeable membranes
• A semipermeable membrane only lets the
solvent molecules through
• Examples
– Cell walls
– Parchment
– Cellophane
48 CHEM1405

49. Osmosis
49 CHEM1405

50. Osmotic Pressure
The osmotic pressure of a solution is the
pressure that must be applied to the
solution to prevent the flow of solvent
molecules into the solution when the
solution and pure solvent are separated
by a semipermeable membrane.
The higher the osmolarity the greater the
osmotic pressure
50

52. Osmosis:
The flow of solvent from a solution of low concentration
to high concentration or flow of solvent from a solution of
low concentration to pure solvent compartment through a
semi-permeable membrane is called as Osmosis.
Semi-permeable membrane is selective membrane which
does not permit the passage of dissolved solute particles.
Or Membrane allows to pass solvent molecules form it , is
known as Semi-permeable membrane.
Semi-permeable membranes used are thin films of
cellulose acetate, polymethyl acrylate and polyamide
polymers are used.

53. 53
The flow continues till the concentration is equal on both the sides.
The pressure created by the phenomenon of osmosis, is called as
‘osmotic pressure’. OR
The external pressure applied to stop the phenomenon of osmosis is
called as ‘osmotic pressure’.