Unit 1: Water treatment

❖ Water Hardness: The hardness of water arises due to the high mineral content.
✓ Hard water is formed when water percolates through deposits of limestone, chalk, or
gypsum, which are largely made up of calcium and magnesium carbonates,
bicarbonates, and sulfates.
✓ Hard water does not lather with soap but instead forms a precipitate i.e. soap scum.
2C17H35COONa + CaCl2/MgCl2 → (C17H35COO)2 Ca/Mg + 2NaCl
soap (soluble) salts (soluble) insoluble scum
✓ Long-term use of hard water causes the formation of limescale in vessels e.g., kettles
and water heaters for domestic purposes. However, it can create critical problems in
industrial settings, where water hardness is monitored to avoid costly breakdowns in
boilers, cooling towers, and other equipment that handles water.
✓ Rainwater and distilled water are soft because they contain comparatively fewer ions.
❖ Representative chemical explanation of the origin of hardness of water:
The following equilibrium reaction describes the dissolving and formation of calcium
carbonate and calcium bicarbonate (on the right):

CaCO3 (s) + CO2 (aq) + H2O (l) ⇌ Ca2+ (aq) + 2 HCO3− (aq)
The reaction can proceed in either direction. Rain containing dissolved carbon dioxide
can react with calcium carbonate and carry calcium ions away with it. The calcium
carbonate may be re-deposited as calcite as the carbon dioxide is lost to the
atmosphere, sometimes forming stalactites and stalagmites.

❖ Types of Hardness: The hardness of water can be classified into two types:
➢ Permanent hardness:
The permanent hardness of water is determined by the concentration of multivalent
cations in the water. Usually, the cations have a charge of 2+. Common cations found
in hard water include Ca2+ and Mg2+. In general, when the soluble salts of magnesium
and calcium are present in the form of carbonates, chlorides, and sulfides in water, it
is called permanent hardness because this hardness cannot be removed by boiling.
These ions enter in a water supply by leaching from minerals within an aquifer.
Common calcium-containing minerals are Calcite and Gypsum. A common
magnesium mineral is Dolomite (which also contains calcium as part of the ore).

➢ Temporary hardness:
Temporary hardness is caused by the presence of dissolved bicarbonate minerals
(calcium bicarbonate and magnesium bicarbonate). When dissolved, these types of
minerals yield calcium and magnesium cations (Ca2+, Mg2+) and carbonate and
bicarbonate anions (CO32− and HCO3−). However, unlike permanent hardness, the
"temporary" hardness can be reduced either by boiling the water or by the addition of
lime (calcium hydroxide) through the process of lime softening. Boiling promotes the
formation of carbonate from the bicarbonate and precipitates calcium carbonate out of
the solution, leaving water that is softer upon cooling.

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❖ Disadvantages of hard water:
✓ When hard water is heated, limescale forms and is deposited in particular places. As a
result, appliances for heating water and water pipes both have furring. The build-up of
deposits in pipes and appliances can result in blockages, and in appliances, it can
reduce energy efficiency and shorten life.
✓ Use of hard water can create critical problems in industrial settings, where water
hardness can cause costly breakdowns in boilers, cooling towers, and other equipment
that handles water.
✓ Washing garments in hard water can make them appear dull and grey, losing all of
their original colors.
✓ With soap or detergents, lathering is challenging. Additionally, using hard water
increases the likelihood of scum build-up, which wastes soap.
✓ Hard water can cause dry skin and hair in people, among other effects.

❖ Water softening processes:

❖ Water softening-lime-soda process:
The soda lime process was used earlier in water treatment to remove hardness from
water. This process is now obsolete but was very useful for the treatment of large
volumes of hard water. Addition of lime (CaO) and soda (Na2CO3) to the hard water
precipitates calcium as the carbonate, and magnesium as its hydroxide. The amounts
of the two chemicals required are can be calculated from the analysis of the water and
stoichiometry of the reactions.

Set-up of Lime-Soda Process for the removal of water-hardness

The stepwise reactions that take place in this process can be attributed as follows:
➢ As slacked lime is added to water, it will react with any carbon dioxide present to ppt
calcium carbonate: Ca(OH)2 + CO2 → CaCO3 ↓ + H2O....(1)
➢ The lime will react with bicarbonates to precipitate corresponding carbonates:
Ca(OH)2+Ca(HCO3)2→2CaCO3↓+2H2O.....(2)
Ca(OH)2+Mg(HCO3)2→MgCO3+CaCO3↓+2H2O.....(3)

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 ➢ Since the magnesium carbonate formed in the medium is soluble in nature, more lime
is added to remove it via its conversion into insoluble magnesium hydroxide:
Ca(OH)2+MgCO3→CaCO3↓+Mg(OH)2↓.....(4)
➢ Magnesium non-carbonate hardness, such as magnesium sulfate is removed via its
conversion into insoluble hydroxide by lime:
Ca(OH)2+MgSO4→CaSO4+Mg(OH)2↓.....(5)
➢ Lime addition removes only magnesium hardness and calcium carbonate hardness but
additionally produces calcium non-carbonate hardness e.g., calcium sulfate as shown
in equation 5.
➢ Soda ash is added to remove calcium non-carbonate hardness by precipitating
insoluble carbonate: Na2CO3+CaSO4→Na2SO4+CaCO3↓.....(6)
➢ pH of about 9.5 and 10.8 are required to precipitate CaCO3 and Mg(OH)2 respectively.
Therefore, an excess lime of about 1.25 meq/l is required to raise the pH.
➢ The amount of lime required can be calculated as: lime (meq/l) = carbon dioxide
(meq/l) + carbonate hardness (meq/l) + magnesium ion (meq/l) + 1.25 (meq/l)
➢ The amount of soda ash required: soda ash (meq/l) = non-carbonate hardness (meq/l)
➔ Problems associated with the process:
✓ After the process of softening, the water will have high pH and will contain the excess
lime and magnesium hydroxide, and calcium carbonate that did not precipitate.
✓ Recarbonation (adding carbon dioxide) is used to stabilize the excess lime and
magnesium hydroxide, which also reduces pH from 10.8 to 9.5 as the following:
CO2+Ca(OH)2→CaCO3↓+H2O and CO2+Mg(OH)2→MgCO3+H2O
✓ Further recarbonation will lower the pH to about 8.5 and stablize the calcium
carbonate as the following: CO2+CaCO3+H2O→Ca(HCO3)2
✓ Thus it is not possible to remove all of the hardness from water. In actual practice,
about 50 to 80 mg/l will remain as a residual hardness.
➔ Limitation of Soda Lime Process:
✓ Lime soda softening cannot produce water completely free of hardness because of the
partial solubility of CaCO3 and Mg(OH)2. Thus, the minimum calcium hardness that
can be achieved is about 30 mg/L as CaCO3, and the magnesium hardness is about 10
mg/L as CaCO3. We normally tolerate a final total hardness on the order of 75 to 120
mg/L as CaCO3, but the magnesium content should not exceed 40 mg/L as CaCO3
(because a greater hardness of magnesium forms scales on heat exchange elements).
✓ Disposal of large amounts of sludge (insoluble precipitate) poses a problem.

❖ Ion exchanger polished water:

Ion exchangers exchange one ion for another, hold it temporarily, and then release it
to a regenerant solution. In an ion exchange system, undesirable ions in the water
supply are replaced with more acceptable ions.
❖ Sodium zeolite softener:
➔ Zeolite: Zeolites are hydrated sodium alumina silicates having a porous structure
with molecular formula Na2O.Al2O3.xSiO2.yH2O (x = 2 to 10 and y = 2 to 6). They

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 are represented as Na2Ze where Ze represents the insoluble framework and Na are the
loosely held sodium ions.
➔ History of the development of zeolite:
✓ In 1905, Gans, a German chemist, used synthetic aluminosilicate materials known as
zeolites in the first ion exchange water softeners. Although aluminosilicate materials
are rarely used today, the term "zeolite softener" is commonly used to describe any
cation exchange process.
✓ The synthetic zeolite exchange material was soon replaced by a naturally occurring
material called Greensand. Greensand had a lower exchange capacity than synthetic
material, but its greater physical stability made it more suitable for industrial
applications. Capacity is defined as the amount of exchangeable ions a unit quantity
of resin will remove from a solution. It is usually expressed in kilograms per cubic
foot as calcium carbonate.

Microscopic view of cellular resin beads (20-50 mesh) of a sulfonated styrene-

divinylbenzene strong acid cation exchanger
✓ The development of a sulfonated coal cation exchange medium, referred to as
carbonaceous zeolite, extended the application of ion exchange to hydrogen cycle
operation, allowing for the reduction of alkalinity as well as hardness.

➔ Principle of zeolite process: They are capable of exchanging their loosely bound
sodium ions reversibly with the hardness-producing cations in water (Ca2+ and Mg2+).
➔ Working: It involves two steps:

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 • Water softening: When Ca2+ and Mg2+ ions containing hard water is passed through
a bed of sodium zeolite, the sodium ions are replaced by the calcium and magnesium
ions.
Na2Ze + Ca(HCO3)2 → 2NaHCO3 + CaZe
Na2Ze + Mg(HCO3)2 → 2NaHCO3 + MgZe
Na2Ze + CaSO4 → Na2SO4 + CaZe
Na2Ze + MgSO4 → Na2SO4 + MgZe
• Regeneration: When all sodium ions are replaced by calcium and magnesium ions,
the zeolite becomes inactive and thus needs to be regenerated in order to continue to
the second cycle of working. Brine solution is passed through the bed of inactivated
zeolite where the following reactions are taken place and form Na2Ze is regenerated.
CaZe + 2NaCl → Na2Ze + CaCl2
MgZe + 2NaCl → Na2Ze + MgCl2
➔ Advantages of the zeolite process:
✓ It produces water with about 10 ppm hardness left behind.
✓ There is no danger of sludge formation.
✓ Requires less time and operation is clean.
✓ Process automatically adjusts itself for variation in the hardness of incoming water.
✓ Equipment is compact, and maintenance and operation are easy.
➔ Disadvantages of the zeolite process:
✓ This method only replaces cationic impurities; anions are left behind in the water.
✓ Treated water contains more sodium salts, so this water cannot be used in boilers else
it will cause caustic embrittlement.
➔ Limitations of the zeolite process:
✓ Turbid water cannot be fed as it will clog the pores of the zeolite.
✓ Acidic water cannot be fed as it will destroy the zeolite bed.
✓ Hot water cannot be used as zeolite tends to dissolve in it.
❖ Ion exchange resin softener:
➔ History of the development of ion exchange resin:
✓ Gradually, an anion exchange resin (a condensation product of polyamines and
formaldehyde) was developed. The new anion resin was used with the hydrogen cycle
cation resin in an attempt to demineralize (remove all dissolved salts from) water.
However, early anion exchangers were unstable and could not remove such weakly
ionized acids as silicic and carbonic acid.
✓ In the middle 1940's, ion exchange resins were developed based on the
copolymerization of styrene cross-linked with divinylbenzene. These resins were very
stable and had much greater exchange capacities than their predecessors. The
polystyrene-divinylbenzene-based anion exchanger could remove all anions,
including silicic and carbonic acids. This innovation made the complete
demineralization of water possible.
✓ Polystyrene-divinylbenzene resins are still used in the majority of ion exchange
applications. Although the basic resin components are the same, the resins have been

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 modified in many ways to meet the requirements of specific applications and provide
a longer resin life. One of the most significant changes has been the development of
the macro reticular, or macroporous, resin structure.
✓ Standard gelular resins have a permeable membrane structure. This structure meets
the chemical and physical requirements of most applications. However, in some
applications, the physical strength and chemical resistance required of the resin
structure is beyond the capabilities of the typical gel structure. Macroreticular resins
feature discrete pores within a highly cross-linked polystyrene-divinylbenzene matrix.
These resins possess a higher physical strength than gels, as well as a greater
resistance to thermal degradation and oxidizing agents. Macroreticular anion resins
are also more resistant to organic fouling due to their more porous structure. In
addition to polystyrene-divinylbenzene resins, there are newer resins with an acrylic
structure, which increases their resistance to organic fouling.

Macroreticular anion resin Polystyrene-divinylbenzene resin

✓ In addition to a plastic matrix, ion exchange resin contains ionizable functional
groups. These functional groups consist of both positively charged cation elements
and negatively charged anion elements. However, only one of the ionic species is
mobile. The other ionic group is attached to the bead structure. Ion exchange occurs
when raw water ions diffuse into the bead structure and exchange for the mobile
portion of the functional group. Ions displaced from the bead diffuse back into the
water solution.
➢ Classifications of ion exchange resins:
• Cation Exchange Resins (RH+): These are phenol-sulphonic acid-formaldehyde
resin and styrene-divinylbenzene copolymers that exchange their H+ ions with the
cations present in the water i.e., Ca2+ and Mg2+.

• Anion Exchange Resins (ROH): These are basically styrene-divinyl benzene or

amine-formaldehyde copolymers containing quaternary ammonium

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 tertiarysulphonium or amino group in the resin. The resin upon treatment with hard
water is capable of exchanging different anions like Cl- or SO42- with its OH-.

➢ Purification of water by ion exchange process:

✓ The ion exchange process consists of two columns- The cation exchanger column and
the anion exchanger column.
✓ First hard water is passed through a cation exchanger which exchanges hardness
causing
cations like Ca2+, Mg2+, Fe2+, etc in water with H+ ions held loosely on the porous
cation exchange resin.
✓ Then hard water is passed through an anion exchanger which exchanges hardness
causing
anions like SO42-, Cl- etc in water with OH- ions held loosely on the porous anion
exchange resin.
✓ The H+ and OH- ions thus released in water by the cation and anion exchangers
respectively combine to form a water molecule.
✓ The water coming out of the columns will be free from hardness causing cations as
well as anions and thus it is known as deionized or demineralized water.

Set-up of the ion-exchange resin process

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 ➢ Reactions:
Step 1: Cation exchanger - 2R−H +Ca+2 ⇌ R2−Ca + 2H+ (R = insoluble matrix)
Anion exchanger – R’−OH +Cl- ⇌ R’Cl + OH- (R = insoluble matrix)
Step 2: After some time, these two exchanges are exhausted when all their H+ and
-
OH ions are replaced by hardness-causing ions. At this stage, the hard water supply
is stopped and cation and anion exchangers are regenerated by treating with acid and
base respectively.
R2Ca2+ + 2H+ → 2RH+ + Ca2+
R’2SO42+ + 2OH- → 2 R’OH- + SO42-
R’Cl + OH- → R’OH + Cl-

❖ Boiler feed water:

➢ Boiler: A boiler is a device for generating steam, which consists of two principal
parts: the furnace, which provides heat, usually by burning fuel, and the boiler proper,
a device in which the heat changes water into steam. The steam or hot fluid is then
recirculated out of the boiler for use in various processes in heating applications.

Boiler-feed water is specially conditioned water that is fed into the boiler to generate
Steam or Hot water.
➢ Composition of Boiler-feed water: The boiler receives the feed water, which
consists of a varying proportion of recovered condensed water (return water) and fresh
water, which has been purified in varying degrees (make-up water). The make-up
water is usually natural water either in its raw state or treated by some process before
use. Feed-water composition, therefore, depends on the quality of the make-up water
and the amount of condensate returned to the boiler.

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 ➢ Treatment of boiler-feed water and maintenance of boiler: The steam, which
escapes from the boiler, frequently contains liquid droplets and gases. The water
remaining in liquid form at the bottom of the boiler picks up all the foreign matter
from the water that was converted to steam. The impurities must be blown down by
the discharge of some of the water from the boiler to the drains. The permissible
percentage of blown down at a plant is strictly limited by running costs and initial
outlay. The tendency is to reduce this percentage to a very small figure.
Proper treatment of boiler feed water is an important part of operating and
maintaining a boiler system. As steam is produced, dissolved solids become
concentrated and form deposits inside the boiler. This leads to poor heat transfer and
reduces the efficiency of the boiler. Dissolved gasses such as oxygen and carbon
dioxide will react with the metals in the boiler system and lead to boiler corrosion. In
order to protect the boiler from these contaminants, they should be controlled or
removed, through external or internal treatment. For more information check the
boiler water treatment web page.

❖ Boiler Problems: If the water used for steam making in the boiler does not satisfy
the specified requirements for the boiler feed water, the development of boiler
problems occurs. There are many types of boiler problems. They are:
➢ Carryover: The process of carrying of water by steam along with the impurities is
called carryover. The phenomenon occurs due to priming and foaming.

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 ➔Priming: When a boiler is steaming (i.e., producing steam) rapidly, some particles
of the liquid water are carried along with the steam. This process of 'wet steam'
formation is called priming.
➢ Causes of Priming:
1. Presence of a large amount of dissolved solids;
2. High steam velocities,
3. Sudden boiling;
4. Improper boiler design;
5. Sudden increase in steam-production rate.

➔Foaming: It is the production of persistent foam or bubbles in boilers, which do not

break easily. Foaming is due to the presence of substances like oils (which greatly
reduce the surface tension of the water).
➢ Priming and foaming, usually, occur together. They are not acceptable because;
❖ dissolved salts in boiler water are carried by the wet steam to the super-heater and
turbine blades, where they get deposited as water evaporates. This deposit reduces
their efficiency,
❖ dissolved salts may enter the parts of other machinery, where steam is being used,
thereby decreasing the life of the machinery;
❖ actual height of the water column cannot be judged properly, thereby making the
maintenance of the boiler pressure becomes difficult.
➢ Priming can be avoided by:
(i) fitting mechanical steam purifiers;
(ii) avoiding rapid changing steaming rate;
(iii) maintaining low water levels in boilers,
(iv) efficient softening and filtration of the boiler-feed water.

➢ Foaming can be avoided by:

(i) Adding anti-foaming chemicals like castor oil,
(ii) Removing oil from boiler water by adding compounds like sodium aluminates.

❖ Boiler Corrosion
Boiler corrosion is the decay of boiler material by a chemical or electrochemical
attack by its environment. The main reasons for boiler corrosion are:
➢ Dissolved oxygen: Water usually contains about 8 ml of dissolved oxygen per litre
at room temperature. Dissolved oxygen in water, in presence of prevailing high
temperature, attacks boiler material:
2 Fe + 2H2O + O2 → 2 Fe(OH)2
4 Fe(OH)2 + O2 → 2 (Fe2O3.2H2O)
Ferrous hydroxide Rust

➢ Removal of dissolved oxygen:

By adding the calculated quantity of sodium sulfite or hydrazine or sodium sulfide.
2 Na2SO3 + O2 → 2 Na2SO4
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 N2H4 + O2 → N2 + 2 H2O
Na2S + 2 O2 → Na2SO4
➢ Dissolved carbon dioxide: Dissolved CO2 has a slow corrosion effect on the boiler
material. CO2 is also released inside the boiler if the water used for steam generation
contains bicarbonates.
CO2 + H2O → H2CO3
Mg(HCO3)2 → MgCO3 + H2O + CO2
➢ Removal of CO2:
(1) By adding the calculated quantity of ammonia. Thus,
2NH4OH + CO2 → (NH4)2CO3 + H2O
(2) By mechanical-aeration process along with oxygen.
(3) Acids from dissolved salts: Water containing dissolved magnesium salts liberate
acids on hydrolysis, e.g.,
MgCl2 + 2H2O → Mg(OH)2 + 2HCl
The liberated acid reacts with iron (of the boiler) in chain-like reactions producing
HCI again and again.
Fe + 2HCI → FeCl2 + H2
FeCl2 + 2H2O → Fe(OH)2 + 2HCl
Consequently, the presence of even a small amount of MgCl2 will cause corrosion of
iron to a large extent

❖ Caustic embrittlement:
Caustic embrittlement is the phenomenon, during which the boiler material becomes
brittle due to the accumulation of caustic substances.
It is a type of boiler corrosion, caused by using highly alkaline water in the boiler.
During softening process by lime-soda process, free Na2CO3 is usually present in
small proportion in the softened water. In high-pressure boilers, Na2CO3 decomposes
to give sodium hydroxide and carbon dioxide,
Na2CO3 + H2O → 2NaOH + CO2

This makes the boiler water basic ["caustic"]. The NaOH-containing water flows into
the minute hair cracks, always present in the inner side of the boiler, by capillary
action. Here, water evaporates and the dissolved caustic soda concentration increases
progressively. This caustic soda attacks the surrounding area, thereby dissolving the
iron of the boiler as sodium ferrate this causes embrittlement of boiler parts,
particularly stressed parts (like bends, joints, rivets, etc.), causing even failure of the
boiler.
➢ Caustic embrittlement can be avoided:
1. By using sodium phosphate as softening agent, instead of sodium carbonate;
2. By adding tannin or lignin to boiler water, since these blocks the hair-cracks, thereby
preventing infiltration of caustic soda solution in these;

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 3. By adding sodium sulfate to the boiler water. Na2SO4 also blocks hair cracks, thereby
preventing the infiltration of caustic soda solutions. It has been observed that caustic
cracking can be prevented if Na2SO4 is added to the boiler water.

❖ Expressions and mathematical problems:

➢ Expression of Hardness:
Both temporary and permanent hardness are expressed in ppm (parts per million) as
CaCO3. The choice of CaCO3 is due to the fact that its molecular weight is 100 and its
equivalent weight is 50 and it is a very less soluble salt in water (around 15-20 mg/l).

Equivalent of CaCO3 =

➢ Units of hardness
1. Parts per million (ppm)
It is defined as the number of parts of CaCO3 equivalent hardness per 106 parts of
water.
2. French degree (oFr)
It is defined as the number of parts of CaCO3 equivalent hardness per 105 parts of
water.
3. Clarke’s degree (oCl)
It is defined as the number of parts of CaCO3 equivalent hardness per 70,000 parts of
water.
4. Milligrams per litre (mg/l)
It is defined as the number of milligrams of CaCO3 equivalent hardness per 1 litre of
water.
➢ Relationship between various units:
1 ppm = 1 mg/L = 0.1° Fr = 0.07° Cl
1 mg/L = 1 ppm = 0.1° Fr = 0.07° Cl
1 ° Cl = 1.433° Fr = 14.3 ppm = 14.3 mg/L
1 ° Fr = 10 ppm = 10 mg/L = 0.7° Cl

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➢ Problems:
Problem-1: A sample of water is found to contain the following dissolving salts in
milligrams per liter Mg(HCO3)2 = 73, CaCl2 = 111, Ca(HCO3)2 = 81, MgSO4 = 40
and MgCl2 = 95. Calculate temporary and permanent hardness and total hardness.
Name of the Amount of the Molecular weight Amounts
hardness- hardness causing of hardness equivalent to
causing salts salts (mg/Lit) causing salts CaCO3 (mg/Lit)
Mg(HCO3)2 73 146 73×100/146 = 50
CaCl2 111 111 111×100/111 = 100
Ca(HCO3)2 81 162 81×100/162 = 50
MgSO4 40 120 40×100/120 = 33.3
MgCl2 95 95 95×100/95 = 100

Temporary hardness = Mg(HCO3)2 + Ca(HCO3)2 = 50 + 50 = 100mg/Lit.

Permanent hardness = CaCl2 + MgSO4 + MgCl2 = 100 + 33.3 + 100 = 233.3mg/Lit.
Total hardness = Temporary hardness + Permanent hardness = 100 + 233.3
=333.3mg/Lit.
Problem-2: A sample of water is found to contain the following dissolving salts in
milligrams per litre Mg(HCO3)2 = 16.8, MgCl2 = 12.0, MgSO4 = 29.6 and NaCl = 5.0.
Calculate temporary and permanent hardness of water.

Name of the Amount of the Molecular weight Amounts equivalent

hardness-causing hardness-causing of the hardness- to
salts salts(mg/Lit) causing salts CaCO3 (mg/Lit)
Mg(HCO3)2 16.8 146 16.8×100/146 = 11.50
MgCl2 12.0 95 12.0×100/95 = 12.63
MgSO4 29.6 120 29.6×100/120 = 24.66
NaCl 5.0 NaCl does not contribute any hardness to
waterhence it is ignored.
Temporary hardness = Mg(HCO3)2 = 11.50mgs/Lit.
Permanent hardness = MgCl2 + MgSO4 = 12.63 + 24.66 = 37.29mgs/Lit.
Problem-3: A sample of water is found to contain following analytical data in
milligrams per litre Mg(HCO3)2 = 14.6, MgCl2 = 9.5, MgSO4 = 6.0 and Ca(HCO3)2
= 16.2. Calculate temporary and permanent hardness of water in parts per million,
Degree Clarke’s and Degree French.
Name of the Amount of the Mol. weight of Amounts equivalent
hardness- hardness-causing the hardness- to
causing salts salts(mg/Lit) causing salts CaCO 3 (mg/Lit)

Mg(HCO3)2 14.6 146 14.6×100/146 = 10

MgCl2 9.5 95 9.5×100/95 = 10
MgSO4 6.0 120 6.0×100/120 = 5
Ca(HCO3)2 16.2 162 16.2×100/162 =10

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Temporary hardness [Mg (HCO3)2 + Ca (HCO3)2] = 10 + 10 = 20mg/Lit
= 20ppm
= 20×0.07°Cl = 1.4°Cl
= 20×0.1°Fr = 2°Fr
Permanent hardness [MgCl2 + MgSO4] = 10 + 5 = 15mg/Lit
= 15ppm
= 15×0.07°Cl = 1.05°Cl
= 15×0.1°Fr = 1.5°Fr
Problem-4: Calculate the amount of temporary and permanent hardness of a water
sample in Degree Clarke’s, Degree French, and Milligrams per Litre which contains
the following impurities.
Ca(HCO3)2 = 121.5 ppm, Mg(HCO3)2= 116.8 ppm, MgCl2 = 79.6 ppm and CaSO4 =
102 ppm.

Name of the Amount of the The molecular Amounts equivalent

hardness-causing hardness causing weight of to CaCO3 (ppm)
salts salts(ppm) hardness-causing
salts
Ca(HCO3)2 121.5 162 121.5×100/162 = 75
Mg(HCO3)2 116.8 146 116.8×100/146 = 80
MgCl2 79.6 95 79.6×100/95 = 3.37
CaSO4 102 136 102×100/136 = 75

Temporary hardness [Mg (HCO3)2 + Ca (HCO3)2] = 75 + 80 = 155 ppm

= 155×0.07°Cl = 10.85°Cl
= 155×0.1°Fr = 15.5°Fr
= 155×1mg/Lit = 155 mg/Lit
Permanent hardness [MgCl2 + CaSO4] = 10 + 5 = 15mg/Lit = 15ppm
= 15×0.07°Cl = 1.05°Cl
= 15×0.1°Fr = 1.5°Fr
Problem-5: 50 ml of standard hard water containing 1 gram of pure CaCO3 per liter
consumed 20 ml of EDTA. 50 ml of hard water consumed 25 ml of the same EDTA
solution EBT indicator. Calculate the total hardness of the water sample in ppm.
Strength of standard hard water sample (CaCO3 solution) M1=
Weight of CaCO3 × 1000
Mol. wt ofCaCO3 1000
= 1 gm × 1000
100 1000
= 0.01M

Strength of EDTA solution M2 = V1 M1 = 50 × 0.01 = 0.025 M

V2 20

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V1 = Volume of standard hard water (50 ml), M1 = Strength of standard hard water
(0.01M)
V2 = Volume of EDTA solution (20 ml), M2 =Strength of EDTA solution =?
Calculation of Total hardness M3 = V2 M2 = 25 × 0.025 = 0.0125 M
V3 50
V2 = Volume of EDTA solution (25 ml), M2 =Strength of EDTA solution= 0.025M
V3 = Volume of sample hard water (50 ml), M3 = Strength of sample hard water =?

Total Hardness = 0.0125 × 105 ppm

= 0.0125 × 100 (Mol. Wt of CaCO3) × 1000 (ml)ppm
= 1250 ppm.

Problem-6: 0.28 grams of CaCO3 were dissolved in HCl and the solution was made
up to one liter with distilled water. 100 ml of the above solution required 28 ml of
EDTA solution on titration. 100 ml of hard water sample consumed 33 ml of the same
EDTA solution EBT indicator. 100 ml of this water after boiling cooling and filtering
required 10 ml of EDTA solution in titration. Calculate the permanent and temporary
hardness of water sample in ppm.

Strength of standard hard water sample (CaCO3 solution) M

= Weight of CaCO3 × 1000
Mol. wt of CaCO3 1000

= 0.28gm × 1000 = 0.0028 M

100 1000

Strength of EDTA solution M2 = V1 M1 = 100 × 0.0028 = 0.01 M

V2 28
V1 = Volume of standard hard water (100 ml), M1 = Strength of standard hard water
(0.0028M)V2 = Volume of EDTA solution (28 ml), M2 = Strength of EDTA
solution=?

Calculation of Total hardness M3 = V2 M2 = 33 × 0.01 = 0.0033 M

V3 100
V2 = Volume of EDTA solution (33 ml), M2 = Strength of EDTA solution (0.01M)
V3 = Volume of sample hard water (100 ml), M3 = Strength of sample hard water =?

Total Hardness = 0.0033 × 105 ppm

= 0.0033 × 100 (Mol. Wt of CaCO3) × 1000 (ml)ppm
= 330 ppm

Calculation of Permanent hardness M4 = V2 M2 = 10 × 0.01 = 0.001 M

V4 100

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V2 = Volume of EDTA solution (10 ml), M2 = Strength of EDTA solution (0.01M)
V4 = Volume of sample hard water after boiling cooling and filtering (100 ml)
M4 = Strength of sample hard water after boiling cooling and filtering =?
Permanent Hardness = 0.001 × 105 ppm
= 0.001 × 100 (Mol. Wt of CaCO3) × 1000 (ml)ppm
= 100 ppm
Calculation of Temporary hardness = Total hardness - Permanent hardness
= 330 – 100 = 230 ppm
Problem-7

Problem - 8
Calculate the carbonate and non-carbonate hardness of a sample of water:

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Problem-9

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Problem-10

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Problem-11

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Problem-12

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Problem-13
A sample of water was found to contain the following analytical data in mgs/lit

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