Section 2: Water

Analysis
 Water Analysis:
Process by which we identify and quantify the chemical
components and the properties of water.

Analysis is carried out on 

 water used in industrial processes
 waste-water stream
 rivers and stream
 Rainfall
 on the sea.

2
 Constituents of Water and Wastewater

PHYSICAL CHARACTERISTICS

• Turbidity
• Color
• Taste
• Odor
• Temperature

3
 CHEMICAL CHARACTERISTICS
1. Nitrogenous compounds
2. Chlorides 9. Biochemical Oxygen Demand `
(BOD)
3. Sulphides
10. Solids
4. Chemical Oxygen Demand
11. Organic Carbon and Volatile
5. Dissolved Oxygen Organic Compounds
6. Metals and cations 12. Phosphorus
(Manganese, Aluminium, Iron, 13. Fats, Oils, Waxes, and Grease
Zinc, Copper, Lead…) 14. Surfactants
7. Water hardness (Ca2+ and Mg2+).
8. pH, Acidity and Alkalinity.

4
 [1] Nitrogen in Water

5
 [1] Nitrogen in water
• Nitrogen is a major component of wastewater
• Protein contains about 16% nitrogen (organic nitrogen)
• Hydrolysis of organic nitrogen by microorganisms
produces Ammonia (free ammonia)
• Nitrites and Nitrates are the result of the oxidation of
ammonia. The nitrite form of nitrogen is very unstable
and is easily oxidized to the nitrate .
• The sum of the free ammonia, nitrite, and nitrate is
called total nitrogen.
• The free ammonia may hydrolyze in water to produce
ammonium ion NH4+ according to the following
equation:
NH3 + H2O ↔ NH4+ + OH- Q. What are the different
forms of nitrogen in water?
6
 [1.a.] Ammonia in water

Sources of Ammonia in water

- From industrial effluents

- Disinfection with chloramines : monochloramine (NH2Cl),
dichloramine (NHCl2) and trichloramine (NCl3).
- Protein decomposition in soil.
- Fertilizers after rainfall.
- Cement mortar used for coating the insides of water pipes
may release considerable amounts of ammonia into
drinking-water

7 WHO standards, 0.05 mg/l.

 [1.a.] Ammonia in water

Effect of pH on Ammonia in water

NH3 + H2O ↔ NH4+ + OH-

 At pH levels below 7, the above  At pH is above 7, the equilibrium is

equilibrium is shifted to the shifted to the left and the
right and the predominant predominant nitrogen species is
nitrogen species is , the ionized ammonia.
form.

 The unionized form is most lethal to aquatic life.

8
 • Useful for low range ammonia nitrogen determinations.

9
 Nessler's reagent method

• Ammonium ions react with Nessler's reagent (Potassium

tetraiodomercurate(II) ), K2[HgI4]
• It forms yellow salt of the ammonobasic mercuric iodide.
At higher concentration of ammonia, it tends to form brown
precipitate. 
• The color obtained is measured either photometrically at
λmax or by Nesslerization technique (A method for
measuring NH3 colorimetrically).

2[HgI4]2- + NH4+ + 4OH- → HgO·Hg(NH2)I  ↓ + 3 H2O + 7I-

Yellow to brown ppt

10
 Salicylate method

• (1) Ammonia combined with hypochlorite to form monochloramine

• (2) then reacts with salicylate to form 5-aminosalicylate.
• (3) Oxidation of 5-aminosalicylate is carried out in the presence of a
catalyst, nitroprusside or [Fe(CN)5NO]2- (also called nitroferricyanide),
results in the formation of indosalicylate, a blue-colored compound.
The blue color is masked by the yellow color (from excess nitroprusside)
causing a green-colored solution. The intensity of the color which is
directly proportional to the ammonia concentration in the sample.

11
 [1.b.] Nitrites and Nitrates in water
 Nitrates in water can cause methemoglobinemia,
(infant cyanosis or blue babies). the iron in
the heme group is in the Fe3+ state, not the Fe2+ of
normal hemoglobin. Methemoglobin cannot bind
oxygen.

 Therefore, Nitrates is a very important parameter in

drinking water standards. The maximum contaminant
level (MCL) for nitrates is 10 mg/L as N.
 The Nitrate concentration is usually determined by
colorimetric methods.
Q. Explain the toxicity of Nitrates
in drinking water?
12
 Methods of Determination of Nitrites in water

Diazotizaiton & Coupling

[Griess-ILosvay method]

Griess test is an analytical chemistry test which

detects the presence of nitrite ion in drinking water.

1- Nitrite is converted to nitrous acid (HNO2)

2- the acid is then diazotized with aromatic amine (sulphanilic acid) to yield
a diazonium salt.
3- the salt is coupled with either :
a) N-naphthyl-(1)-ethylenediamine to produce a red-violet azo dye.
b)Dihydroxybenzoic acid to produce an orange- yellow azo dye.
4- The colored products are measured at the corresponding λmax or by
colorimetric comparison technique.

13
 A

14
 B

Q. What are the oxidized

forms of nitrogen in water?
Which of them is the most
abundant form?

Q. Write the method of

analysis of Nitrites in water?
15
 Methods of Determination of Nitrates in water

Phenol disulphonic acid method

Nitrate reacts with phenoldisulphonic acid (PDA) to

produce a nitro derivative, which in alkaline solution
develops a yellow colour. The colour produced
follows Beer’s law and is proportional to the
concentration of NO3- present in the sample. The
concentration of NO3- is determined using a
colorimeter or spectrophotometer.

16
17
 [2] Chlorides in Water

18
 [2] Chlorine in water
 Chloride concentrations of up to 400 mg/l is safe
 water can taste salty if it contains more than about
100 mg/l Cl-

Forms of chlorine

Free chlorine Combined chlorine

As elemental chlorine (Cl2),

Chloramines or other
hypochlorous acid (HOCl) chloro derivatives.
or hypochlorite ion (OCl-).

Q. What are the different

forms of chlorine in water?
19
 The photometric method is
more sensitive, more precise
and more accurate than the
titrimetric method.

Examples on titrimetric methods:

Mohr, volhard, mercurimetric

20
 Photometric method

A DPD reagent:
 Elemental chlorine Cl2, hypochlorous acid HOCl and
hypochlorite OCl- ion react with N,N-diethyl-1,4-
phenylenediamine (DPD) to form a red colored azo dye

21
 Photometric method

B DPC reagent:
 Mercury Hg(II) ions react with chloride ions to form mercury
(II) chloride.
-Excess mercury (II) ions react with diphenyl carbazone to form
a blue violet complex in a solution acidified with nitric acid.

22
 Photometric method

 Chloride reacts with mercury (II) thiocyanate to form

mercury (II) chloride and chloromercurate (II) inions.

Hg (SCN)2 + 2 Cl-→ HgCI2 + 2 SCN-

Hg (SCN)2 + 4 Cl- → (HgCl4)2- + 2SCN-

The thiocyanate released reacts with iron (III) nitrate in

nitric acid solution to yield blood-red iron thiocyanate.

SCN- + Fe3+→ Fe (SCN)2+

blood-red color
23
 Titrimetric method
(Iodometric titration)

 To the acidified water sample, add KI solution.

Titrate the liberated iodine against st. Na2S2O3 using
starch as indicator.

Cl2 + 2KI → I2 + 2KCl

I2 + 2 Na2S2O3 → 2NaI + Na2S4O6

24
 [3] Sulphides in Water

25
 [3] Sulphides in water
 Most of Sulphides in water exist in the form of Hydrogen
sulphide, H2S

Sources:
 Sulfur-reducing bacteria, which use sulfur as an energy
source, are the primary producers of large quantities of
H2S. These bacteria chemically change natural sulfates
in water to hydrogen sulfide. Sulfur-reducing bacteria
live in oxygen-deficient environments such as deep
wells, plumbing systems, water softeners, and water
heaters.
The microbial breakdown of organic matter in the
absence of oxygen gas is called  Anaerobic Digestion.
 Other sources of sulphides are sewage and leather
26 industries.
 Potential health effects of
hydrogen sulfide in drinking water
 It has odor of rotten eggs.
 It is very poisonous and corrosive.
H2S + 2O2 → H2SO4
 Drinking water is not allowed to contain any hydrogen
sulfide due to its toxicity (does not have a drinking
water standard ).
 The presence of this compound is an indicator of
bacterial water pollution.
 Hydrogen sulfide gas is flammable and at high
concentrations.

27
28
 Photometric method

 Addition of p-aminodimethyl aniline to the sample

29
 Titrimetric method
(Iodometry)

 Water sample is acidified with HCl. Then, known

excess standard iodine (I2) solution is added.
H2S + I2 = 2H+ + 2I- + S↓
Back titrate the excess unused I2 against standard sod.
thiosulphate (Na2S2O3) using starch.

Titration reaction

I2 + 2 Na2S2O3 → 2NaI + Na2S4O6

30
 Treatment
Continuous chlorination
For levels up to 75 mg/L chlorine is used in the purification
process as an oxidizing chemical to react with hydrogen
sulfide. This reaction yields insoluble solid sulfur.
Usually the chlorine used is in the form of sodium
hypochlorite.
Aeration
For concentrations of hydrogen sulfide less than 2 mg/
L aeration is an ideal treatment process. Oxygen is
added to water and a reaction between oxygen and
hydrogen sulfide react to produce odorless sulfate
Nitrate addition
Calcium nitrate is used to prevent hydrogen sulfide
formation in wastewater streams.

31
 [4] Chemical Oxygen
Demand (COD)

32
 [4] Chemical Oxygen Demand ,COD.

It is the amount of oxygen required for the oxidation of the

reducing matter that is present in water. (organic and
inorganic matter)

Significance of COD values:

 COD often is used as a measurement of pollution in

water.
COD = 1 ppm → sample of good purity.
= 3 ppm → sample of medium purity
= 4 ppm → sample of doubtful purity.
> 4 ppm → polluted sample.
33
 Determination of COD

 Organic pollutants in water are determined by oxidation

with amount of O2 that is chemically equivalent to the
dichromate consumed

 The sample is heated with K2Cr2O7

 The organic matter is converted to CO2 and H2O
 The dichromate is converted/reduced to Cr+3
 The excess dichromate is determined by titration with
ferrous ammonium sulphate
34
 The main redox reactions:

Interferences

Any substance in water that reduces Cr2O72- will interfere

with the COD experiment.
One of the common interferences is Cl- which is oxidized
by the dichromate to Cl2
If Chloride is known to be present in the sample, HgSO4 is
added to the reaction mixture to tie up Cl- as soluble
Hg(II) chloride .
35
[5] Dissolved Oxygen (DO)

36
 [5] Dissolved Oxygen, DO.

It is the oxygen already dissolved or present in water

during its aeration. It is a measure of water aeration.
Significance of DO:
 It is very important to detect the amount of DO.
DO-data determine conditions for aquatic life.
DO-data determine conditions affecting corrosion of iron
and steel in water pipes and boilers. (↑ O2 corrosion↑).

37
38
 Winkler's method

1 Mn2+ + 2OH- → Mn(OH)2↓ white ppt.

2 2Mn(OH)2 + ½ O2 + H2O → 2Mn(OH)3 ↓ brown ppt.

3
2Mn(OH)3 ↓ + 6HCl → 2MnCl3 + 6H2O
4
2MnCl3 + 2KI → I2 + 2KCl + 2MnCl2

The liberated iodine is equivalent to DO

I2 + 2Na2S2O3 → Na2S4O6 + 2NaI

39
 Interferences

A) Oxidizing agents B) Reducing agents

Give more liberated I2 than Give less liberated I2 than

the actual amount the actual amount
Example: Fe3+ , NO2-,…. Example: Fe2+ , S2-, SO32- ….
Ox. Agent + KI  I2 Removal is by adding dilute
Removal of Fe3+ by adding MnO4- drop wise to the sample, till
phosphoric acid. By forming the persistence of very faint color.
colorless complex bis(phosphato) Excess MnO4- may be removed by
ferrate(III) adding one drop of dilute Na-
[Fe(PO4) 2] 3−   oxalate solution.
Removal of NO2- : by addition of Hydrazoic acid
HN3 + NO2- + H+ → N2 ↑ + N2O↑ + H2O
40
 Interferences

B) Reducing agents

Give less liberated I2 than

the actual amount
Example: Fe2+ , S2-, SO32- ….
Removal is by adding dilute
MnO4- drop wise to the sample, till
the persistence of very faint color.
Excess MnO4- may be removed by
adding one drop of dilute Na-
oxalate solution.
MnO4- + 5e- + 8H+ → Mn2+ +
4H2O
Fe2+ → Fe3+ +
41 e-
 [6] Cations in Water

42
 [6.a.] Manganese (Mn2+)

Significance

- Manganese is a mineral that naturally

occurs in rocks and soil.
- Although it is an essential, non-toxic
trace element, the maximum limits in
drinking water is 0.05 mg/l, because of
the staining which may be caused.

- In Ground water Manganese present as divalent ion due to

the absence of oxygen
- In the surface water it present in the trivalent and
quadrivalent states

43
 Methods of Determination of Manganese

Atomic absorption
spectrophotometric method

Chemical reactions
Photometric methods

Persulphate
Reaction

44
 Persulphate oxidation method

- Persulphate S2O82- oxidize manganese ion to permanganate

Interferences

One of the common interferences is Cl- (………. Agent) which

is oxidized to Cl2
Cl- may reduce MnO4- back to Mn2+, or reduce S2O82- to
SO42-
This can be eliminated by adding mercuric nitrate Hg(NO3)2
solution which forms stable tetrahedral coordination
45
complex [HgCl ]2−.
 [6.b.] Aluminium ion (Al3+)

Sources
 Aluminium salts are added during
the purification of drinking and
swimming pool water to flocculate
the suspended substances and
contaminants.

Significance

 The maximum aluminium limit allowed is 0.2 mg/l

in drinking water.

46
 Methods of Determination of Al3+

Atomic absorption
spectrophotometric method

Chemical reactions
Photometric method

Eriochrome Cyanine-R Reaction

47
 Eriochrome Cyanine-R Reaction

 Aluminum solution is buffered to a pH 6

 Eriochrome Cyanine R is added
 A red to pink complex is formed which has  max = 535 nm
 The intensity of the color is proportional to the Al3+
concentration.
48
 [6.c.] Iron in water (Fe3+ or Fe2+)
 Hydrated ferric oxide Fe2O3·H2O is the predominant
form of iron in water. But under reducing conditions,
iron exists in Fe2+ state.
Sources
 It may originate from water pipes.
 Iron salts are added to water samples as flocculating
agents to remove suspended matters from water
during purification processes.

significance
 The maximum conc. in public waters is 0.2 mg/l.
 Higher conc. must be removed as it may cause
unaccepted taste and staining problems.
49
 Methods of Determination of iron

Atomic absorption
spectrophotometric method
Chemical reactions

 All Fe3+ should be Reduced to Fe2+ by

boiling with hydroxyl amine or adding
Ascorbic acid

Phenanthroline
Bipyridine method
Reaction

50
 Phenanthroline Reaction

 Reduce the Fe3+ to Fe2+ by boiling with hydroxyl amine or

adding Ascorbic acid
 The pH is adjusted between 3 to 3.5
 Three molecules of 1,10-phenanthroline chelate an atom of
Fe2+ to form an orange-red complex.

51
 Bipyridine Reaction

 Reduce the Fe3+ to Fe2+ by boiling with hydroxyl amine or

adding Ascorbic acid
 The pH is adjusted between 1 to 7
 Three molecules of Bipyridine chelate an atom of Fe2+ to
form an pink-deep red complex.

52
 [6.d.] Zinc ion in water (Zn2+)
Sources
 Zinc most commonly enters the domestic
water supply from the deterioration of
galvanized water pipes made of brass (brass
= mixture of Zn & Cu)
 From industrial waste
 Pb2+ and Cd2+ are the impurities of Zinc in
galvanization process
 When water is left to stand in pipe work, zinc metal, as a
reducing agent, reduces nitrate to nitrite.
significance
 Zinc is essential in body growth. The activity of more than
80 enzymes is zinc-dependent. The daily requirement for
humans is 2 → 10 mg Zn.
 However, > 5mg/l Zinc in water causes bitter taste.
53
 Methods of Determination of Zinc

Atomic absorption
spectrophotometric method

Chemical reactions

Ferrocyanide
Dithizone method
method

Give reason: contamination of water sample by

54 Zinc ions points to the presence of Pb2+ and Cd2+
 Dithizone method

 Zinc reacts with dithizone (diphenyl thiocarbazone) reagent

in weakly acidic medium to form a red compound (zinc
dithizonate) which is extractable with CCl4 and measured
photometrically.

55
 Interferences

Dithizone is not a specific reagent for zinc.

In the pH range 4 → 7 Cu2+, Bi3+, Ni2+, Pb2+, and other
elements can be complexed by the reagent.
These elements can be masked by the addition of KCN
and sodium thiosulfate, by forming stable complexes.

56
 Ferrocyanide method
(Turbidimetric  )

Interferences

 Fe3+ interferes with the determination of zinc, it gives

blue colored complex of Fe3 [Fe(CN)6]2 (Ferrous Ferri
cyanide).
 Sodium sulphite Na2SO3 reduces Fe3+ to Fe2+.

57
 4- write the method
of determination of
the required
component…..

3- solve the problem

of each of the
Lab Case Study: oxidizing
Given a sample of drinking interferences…….
water contaminated with
Zinc ions, illustrate how to
2- write all the oxidizing
analyze the sample after the
contaminants that could
removal of all expected
be present in your
interferences .
sample……..

1- check whether Zn
ion is oxidizing or
Keys to reducing agent…..
answer:
58
 [6.e.] Copper ions (Cu2+, Cu+)

Sources

 CuSO4 is added to water tanks to

control algae growth.

Significances

 Traces of copper is essential for normal body metabolism,

its absence may cause anaemia in children.
 Permissible conc. limit in drinking water according to
WHO is 1 mg/l

59
 Methods of Determination of Cu2+,Cu+

Atomic absorption
spectrophotometric method

Chemical reactions

Diethyl
Cuproine method
dithiocarbamate
method

60 Turbidimetric method 
 Cuproine method

 Copper (I) ions combine with 2,2-biquinoline (cuproine) in

alcoholic-aqueous solution to form a purple red complex.
 copper (II) ions must be reduced prior to the reaction.

61
 Diethyl dithiocarbamate method

 Copper (II) ions combine with diethyl dithiocarbamate to

form Golden yellow complex.
 Absorbance is measured at  max = 435 nm

62
 Turbidimetric method  (Ferrocyanide)

Interferences

 Fe3+ interferes with the determination of zinc, it gives

blue colored complex of Fe3 [Fe(CN)6]2 (Ferrous Ferri
cyanide).
 Sodium sulphite Na2SO3 reduces Fe3+ to Fe2+.

63
 [6.f.] Lead ion (Pb2+)

Sources

 Water stored in tanks and pipes

painted with lead.

Significances

 Lead is a serious poison; it accumulates in the bone

structure and may cause brain damage and death.
 Maximum allowed limit in drinking water 0.1 mg/l.

64
 Dithizone method
(Photometric )

65
 Dithizone method

 Dithizone (diphenylthiocarbazone) reagent reacts with lead

in basic solution containing citrate buffer to give red color
of lead dithizonate complex which is extracted in CHCl3
and measured photometrically.

66
 Interferences

 Interfering elements are Bi3+,Cu2+, Hg2+, Ag+, Zn2+, Sn2+.

 Reduction with hydrazine acetate to lower the oxidation
state of elements that capable of oxidizing the dithiazone.
 The interfering ions are then removed by complexation with
dithiazone at pH 2-3
 Pb2+ is extracted at pH 8-9 (by addition of citrate buffer).

Q: pH meter is an essential
apparatus in the experiment of
determination of Pb2+????

67
68
 [6.g.] Cadmium(Cd2+)

Sources

 Cadmium may enter water from

deterioration of Galvanized pipes.
 From Industrial effluents.

Significances

 Cadmium is highly toxic

 Maximum allowed limit in drinking water 0.4 μg/l.

69
 Dithizone method
(Photometric)

Concentrations of
1. Adjust the pH for the complexation
metal ions found in
water sample do not
2. Cd2+ form red complex with the dithizone
3. The complex is extracted with chloroform
interfere with the
4. The extract is measured photometrically at
Cd2+ measurements?
certain wavelength.
5. Cd2+ conc. Is obtained by standard calibration
70 curve (standard solution of Cd2+)
 [6.h.] Mercury (Hg2+)

Sources
 Levels of mercury in the environment
are increasing due to discharge
from hydroelectric, mining, and paper
industries.

Significances

 Mercury is highly toxic

 No standards for mercury or its salts (not allowed to
present in the potable water).
Minimum detectable quantity is 1μg/l

71
 (Photometric)

1. A colored complex is
formed between Hg(II)
and 2-(2-
benzothiazolylazo)-p-
cresol.
2. mercury in the form of a
complex is extracted
and determined
spectrophotometrically
at 650 nm
72
 [7] Water hardness
2+
Ca &Mg 2+

73
 Types of hardness
•Generally hardness is due to Ca2+, Mg2+ (mainly) and Fe3+ ions.

Temporary hardness Permanent hardness

 Due to the presence  Due to the presence of

of calcium and sulphates, chlorides and
magnesium as nitrates of calcium and
bicarbonate. magnesium.
 Temporary hardness
is destroyed and
removed by boiling.

74
 Classification of water
Waters are commonly classified in terms of the degree of hardness.

Type water sample Hardness in terms of

mg CaCO3/L

Soft water 0-75 ppm

Moderately Hard water 75-150 ppm

Hard water 150-300 ppm

very Hard water 300ppm or more

75
76
 Palmitate method for (Total hardness)
The hard water sample is titrated with standard solution of
potassium palmitate. Palmitate anion precipitates Ca2+/
Mg2+ cation producing insoluble Ca & Mg palmitates. Any
excess amount of the palmitate solution will be hydrolysed
rendering the solution alkaline to ph.ph.

During titration :
K-palmitate + CaCl2→ Ca-palmitate + 2KCl
MgCl2 →Mg - palmitate
(white precipitates)
At the end point:
Hydrolysis
K palmitate → KOH + palmitic acid (salt of weak acid)
(pink
77 colour with ph.ph.)
 Palmitate method

For magnesium hardness alone, the calcium

should be first precipitated as Ca-oxalate.
For the determination of permanent hardness only,
the temporary hardness is first removed by boiling.

78
 ETDA method

*(For total Ca2+ and Mg2+ contents)

• water sample + buffer pH= 10 using
NH4Cl/NH4OH
• titrate with st. EDTA using Erio-T
indicator.

* For calcium hardness alone :

• water sample + NaOH to pH=12
• titrate against st. EDTA using Murexide
indicator.
• Mg hardness is measured by difference.

79
[8] Water alkalinity, Basicity
and pH

80
It is caused by dissolved It is usually caused by the
carbon dioxide "free presence of strong or
carbonic acid", mineral weak bases dissolved in
acids and salts of strong water (e.g. carbonate,
acids and weak bases. bicarbonate, phosphate,
silicate and borate …).

It is determined potentiometrically, using pH-meter.

The determination of water acidity, alkalinity and pH gives an

indication of the degree of the corrosivity of water.
81
 Water acidity (Base capacity)
This determination is important in water analysis as a
basis for calculating the dissolved carbon dioxide
content.
*Determination : (Titrimetry)
 (a) Total acidity:
water sample is titrated ≠ st. alkali (NaOH) using ph.
ph. indicator.
 (b) Mineral acids acidity:
water sample is titrated ≠ st. alkali (NaOH) using M.
O. indicator.
* The acidity is calculated as ppm CaCO3.
Eq.wt. of
CaCO3 x
(N  V)  50000
Acidity as mg/l CaCO 3  NaOH
1000
ml sample

82
 Water Basicity (Acid capacity)

Determination: (Titrimetry)
 (a) Phenophthalein alkalinity :
Titrate water sample against st. acid using
ph.ph. indicator.
 (b) Methyl orange alkalinity :
Titrate ≠ st. acid using M.O. indicator.
 The alkalinity is calculated as ppm CaCO3.

(N  V)  50000
Alkalinity or [Alk] T as mg/l CaCO 3  HCl
ml sample

83
 Reference:

Standard Methods for the

Examination of Water and
Wastewater
22nd Edition, American Public
Health Association, 2012
ISBN 9780875530130

84