SECTION – A
1.PHASE RULE
TERMINOLOGY:
GIBBS PHASE RULE: For a heterogenous system in equillibrium at a definite
temperature and pressure, the number of degree of freedom is greater than the
difference in the number of components and the number of phases by two in which the
equillibrium is not influenced by external effects such as gravity, electrical or magnetic
forces such as gravity, electrical or magnetic forces, surface tension.
F = C - P+ 2
PHASE: Any homogenous and physically distinct part of a system which is bounded by
a surface and is mechanically separable from the other part of the system is called
phase.
eg. (1)The decomposition of CaCO3 into CaO and CO2 in a closed vessel constitutes a
three phase system.
CaCO3(s)
CaO(s) + CO2
(2) Fe(s) + H2O (g)
FeO(s) + H2 (g), there are two solid Fe and FeO and one
gaseous phase consisting of H2O(g) and H2(g). Thus , three phase exist in equillibrium .
COMPONENT: The number of component of a system is defined as the smallest
number of independently variable constituents in which the composition of each phase
of a heterogeneous system can be expressed directly or in the form of a chemical
equation.
eg. (1)In the dissociation of NH4Cl in a closed vessel,
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NH4Cl(s)
NH4Cl(g)
NH3(g) + HCl (g) , the proportion of of NH3 and HCl are
same hence the number of component is one if NH3 and HCl is in excess , the system
becomes two component.
(2) Dissociation of KClO3 in a closed vessel
2KClO3 (s)
2KCl(s) + 3O2 (g), it is two component system
DEGREE OF FREEDOM: The degree of freedom of a system is defined as the
minimum number of independently variable factors such as temperature, pressure and
concentration which must be specified in order to define the system completely.
F = 0 (non variant)
F= 1 (univariant)
F= 2 (bivariant)
F= 3 (Trivarinat)
eg. For the gaseous mixture of N2 and H2, P= 1, C=2 , F = C-P+2 so F=2, bivariant
system.
ONE COMPONENT SYSTEM:
WATER SYSTEM
H2O(s)
H2O(l)
H2O(g)
Phase -3, component- 1
PHASE DIAGRAM
C
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Fig : Phase diagram of water system
1. Curves- OA, OB, OC (univariant)
2. point- triple point O (non variant)
3. Areas- BOC, COA, area below AOB (bivariant)
4. Metastable equilibrium(Supercooled water/ vapour system)system) curve
urve OA’
2. CARBONDIOXIDE SYSTEM
CO2(s)
CO2(l)
CO2(g)
Phase -3, component- 1
PHASE DIAGRAM
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Fig: Phase diagram of Carbon dioxide system
1.Curves- AB (sublimation), BD (vaporization), BC (fusion) univariant 2.Areas- ABC,
CBD, ABD (bivariant) 3.Triple point- B
Variation in either temperature/ pressure
1. Keeping the temperature constant
2. Keeping the pressure constant
TWO COMPONENT SYSTEM: studied in the form of condensed system
Condensed system: Two component solid-liquid system having no gas phase is called
condensed system.
Reduced phase rule equation: F’= C- P+ 1
SIMPLE EUTECTIC SYSTEM: solid solution of two components having the lowest
melting point of all possible mixtures of the components is called an eutectic mixture
and binary mixture forming an eutectic mixture at a particular composition is called
an eutectic system
LEAD-SILVER SYSTEM
Phase- i, Ag(s) ii, Pb(s) iii, solution of molten Ag and Pb, F’= C-P+ 1 can be used
Component-2
1.Curves- AC( freezing point curve of silver), BC(freezing point curve of Pb) univariant
2. Point –C (Eutectic point) non variant, 3. Areas- i above AOC (bivariant), ii ACD
(univariant) iii BCE (univariant) iv, DCHF (univariant) v CEGH (univariant)
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o
961 C A
Liquid Solution (Pb-Ag)
Temperature
X
Liquid (Pb-Ag) + Ag (S)
Y
o
B 327 C
Pb (S)
+
Liquid (Ag-Pb)
o
303 C C
O
Ag (S) + Eutectic mixture
E
D
Pb (S) + Eutectic mixture
F
Ag 100%
Pb 0 %
G
Ag 2.6 %
Pb 97.4 %
Ag 0 %
Pb 100 %
Composition
Fig. Phase diagram of Lead-Silver system
Applicaton of phase diagram for desilverization of Argentiferrous lead (Pattinsons
process)- increases the % of Ag in argentiferrous lead. The eutectic mixture containing
2.6% Ag can be treated for recovery of Ag.
SYSTEM FORMING COMPOUNDS WITH CONGRUENT MELTING POINT :
When the components of a binary system at a particular stage form a compound which
melts at a sharp temp to give a liquid of the same composition as that of solid and the
temp at which the compound melt is called congruent melting point.
ZINC- MAGNESIUM SYSTEM
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Phases i, Zn(s) ii, Mg(s) iii MgZn2(s) iv Liquid solution of Zn and Mg component-2
PHASE DIAGRAM
B
Liquid Solution
651oC
D
Temperature
575oC
Congruent M.Pt.
419oC A
Zn +
Liquid
380oC F
MgZn2 + Liquid
solution
C
Eutectic point
G
Eutectic point
E
Mg + MgZn2
Zn + MgZn2
100% Zn
0% Mg
Mg + Liquid Solution
345oC
H
0% Zn
100% Mg
100% MgZn2
Composition
Fig.
Phase diagram of Zn & Mg system
1.Curves i, AC (freezing point curve of Zn ) univariant ii CDE (univariant ) iii BE
(freezing point curve of Mg (univariant)
2. i, Point –D (congruent melting point) non variant ii Point- C (eutectic point)
nonvariant iii Point E(eutectic point) nonvariant
3. Areas- i above ACDEB
SYSTEM FORMING COMPOUNDS WITH INCONGRUENT MELTING POINT :
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When unstable compound is heated, instead of melting at a sharp temp, it decomposes
much below its M.P to form a new solid phase and a solution whose composition is
different from that of solid phase. Such compound posesess an incongruent M.P .
S1
Original solid
S2
+
solution
New solid
SODIUM SULPHATE – WATER SYSTEM
Phases i Na2SO4. 10 H2O(decahydrate) ii Na2SO4. 7 H2O (heptahydrate) iii Rhombic
Na2SO4 iv, Monoclinic Na2SO4 v solid ice vi. Solution
Component-2
PHASE DIAGRAM
1.Curves i, AB (M.P curve of ice) univariant ii BC (solubility curve of decahydrate)
univariant iii curve CDE (solubility curve of anhydrous rhombic salt) univariant iv
Curve EF solubility curve of monoclinic Na2SO4 univariant
2. Points i Point B (Eutectic point) (univariant) ii point C (Incongruent M.P)
(univariant) iii point E (Incongruent M.P) (univariant)
3. Metastable Equillibrium 1.Curves i, curve CC’ (solubility curve of metastable
Na2SO4. 10 H2O) ii curve CH (solubility curve of metastable rhombic Na2SO4) iii curve GH
(solubility curve of metastable Na2SO4. 7 H2O)
2. Points i. Point G (metastable eutectic point) ii Point H (Incongruent/ transition
point)
Cooling Curves: The shape of the freezing point curves can be determined by thermal
analysis.
Thermal analysis is a method involving a study of cooling curves of various compositions
of a system during solidification.
There are two consideration1. When a pure substance in the fused or liquid state
2. When a mixture of two solids in fused state
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2.CATALYSIS
CATALYST: A catalyst is a substances which alters the rate of chemical reaction without
being used up in the reaction and can be recovered chemically unchanged at the end of
the reaction.
POSITIVE CATALYST: The catalyst which increases the rate of reaction is called positive
catalyst. eg. 1. Decomposition of potassium chlorate in the presence of small amount of
MnO2
M nO
2KClO3
2KCl + 3O2
2
2. Manufacture of ammonia by Haber’s process using finely divided iron as a catalyst
N2(g) + 3H2(g)
F e (S )
2NH3(g)
NEGATIVE CATALYST: The catalyst which decreases the rate of reaction is called
negative catalyst. eg.
1. Decomposition of H2O2 is retarded in the presence of acetanilide
2H2O2 (l)
A c e t a n ilid e ( s )
2H2O (l) + O2 (g)
2 In the contact process, the rate of combination of SO2 and O2 is slowed down by
arsenic compound or V2O5 as a catalyst
2SO2 + O2
V 2O 5
2SO3
Characteristics of catalysed reaction:
1.
A catalyst does not initiate the reaction eg
Room temp
H2 + O2
No reaction
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Pt black
2H2 + O2
2H2O
2. A small quantity of the catalyst is generally required eg.
C6H6 + C2H5Cl
A lC l 3
C6H5C2H5 + HCl
3. A catalyst remain unchanged in mass and chemical composition at the end of the
reaction.
eg. MnO2 used in granular form as a catalyst in thermal decomposition of KClO3 is
left as fine powder at the end of the reaction.
4. A catalyst is specific selective in its action. eg.
Al2O3
C2H5OH
Al2O3
C2H5OH
C2H4 + H2O (dehydration)
C2H4 + H2 (dehydrogenation)
5. A catalyst has an optimum temperature eg.
2SO2
+
O2
Pt
450-5000C
2SO3
6. Activity of of the catalyst is increased by the presence of promoter
eg. In the manufacture of NH3 by Haber’s process
N2(g) + 3H2(g)
Fe(catalyst)
Mo(promotor)
2NH3(g)
7. A catalyst is poisoned by the presence of certain substances
Some powerful catalytic poison HCN, H2S, CO, AS2O3
Type of catalysis: 1. Homogenous catalysis
2. Heterogenous catalysis
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1. Homogenous catalysis: When the reactants and catalyst are in the same phase
and the reaction system is homogenous throughout, the catalysis is termed as
homogenous catalysis.
eg. 1. Oxidation of SO2 into SO3 by oxygen in the presence of NO.
NO(g)
2SO2(g) + O2(g)
2SO3
2. Decomposition of acetaldehyde in the presence of iodine vapours .
CH3CHO(g)
I2 vapours
CH4(g)
+
CO(g)
2. Heterogenous catalysis: When the reactants and catalyst are in the different
phase and the reaction system is heterogenous throughout, the catalysis is
termed as heterogenous catalysis.
eg. 1. Combination of N2 and H2 in the presence of finely divided iron (Haber’s
process)
N2(g)
+ 3H2
Fe(S)
450-5000 C
2NH3
2.Oxidation of NH3 by O2 in the presence of platinum gauze (Ostwald process)
4NH3(g) + 5O2(g)
Pt(s)
4NO(g)
+ 6H2O
Mechanism of homogenous catalytic reaction:
Intermediate compound formation theory: “ The catalyst forms very reactive and
unstable intermediate compound with reactants which immediately reacts with other
reactants yielding the product of the reaction and liberating the catalyst in its original
composition”
eg. Williamson’s etherification process in the presence of H2SO4 as a catalyst
C2H5OH + H2SO4 →
Reactant
catalyst
[C2H5HSO4] + H2O
Intermediate
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[C2H5HSO4] + CH3OH → C2H5OCH3 + H2SO4
C2H5 OH + CH3OH H2SO4→ C2H5OCH3 + H2O
Mechanism of heterogenous catalytic reaction
Adsorption or contact theory: It consist of the following steps
1. Adsorption of reactant molecules- The reactant molecules diffuses to the surface
of catalyst and get adsorbed. The force are either weak vanderWaal’s forces( in case
of physical adsorption) or valence bond forces(in case of chemiadsorption)
2. Formation of activated complex- Adsorption is an exothermic reaction and involves
liberation of heat. The heat evolved weakens or even breaks some of bonds within
the adsorbed reactant molecules.Therefore the adsorbed molecule get activated.
Due to this the molecule adjacent to one another join to form an activated complex.
3. Decomposition of activated complex - The activated complex being unstable
decomposes to yield the product. The product formed hold the catalyst surface by
partial chemical bonds.
4. Desorption of product- The product are desorbed from the catalyst surface. The
catalyst surface is again free for the adsorption of fresh reactant molecules.
eg. Hydrogenation of ethane to ethene in the presence of Ni catalyst
Catalytic promoters: Certain substances were found to increase the activity of
catalyst, although they are not considered as catalyst. these substances are called
promoters or activators.
eg. 1. In the Haber’s process for the manufacture of NH3 from H2 and N2, Mo and
(Al2O3 + k2O) is used as a promoter.
N2(g) + 3H2(g)
Fe
2NH3(g)
Mo/Al2O3,K2O
2. In the Bosch ‘s process, for the manufacture of hydrogen from the water gas, finely
divided iron is used as catalyst and metallic copper is used as a promoter.
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Mechanism of Action of catalytic promoters:
Active centers: Surface of the catalyst is not uniform , there are a number of edges,
peaks and cracks. The catalytic activity at these sites is relatively high due to the
presence of more residual forces at these spots. These are more active in chemisorbing
the reacting gases to form the adsorbed activated complex. These are referred to as the
active centers.
Catalyic activity: “Catalyst is more efficient in finely divided state”.
The catalytic activity is directly proportional to the surface area. With the increase of
disintegration or subdivision, the free surface area is increased due to the increased in
the number of active sites. Thus large surface area is available for adsorption of
reactant molecules.
The increased in catalytic activity in the presence of a promoter may be due to
(a) Change in lattice spacing: The lattice spacing of the catalyst is increased by the
action of promoters.
(b) Increased in number of active sites: Promoter increase the discontinuities (peaks,
curves, and cracks) the surface of the catalyst increasing the number of active centers.
Catalytic Poisons: Any substance which inhibit or destroy the catalytic activity to
accelerate the reaction is called catalytic poison.
eg. 1. In contact process for the manufacture of H2SO4, catalytic poison AS2O3 absorbs
on the active site of Pt forming PtS on the surface of the Pt reducing the catalytic
activity of Pt.
2.In Haber’s process for the manufacture of ammonia, the iron catalyst used to catalyse
the reaction between H2 and N2 is poisoned by the presence of H2S.
Fe
N2(g) + 3H2(g)
2NH3(g)
poisoned by H2S
TYPE OF CATALYTIC POISON:
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1. Temporary poisoning: In which the catalyst regains its activity when the poison is
removed from the reactants.
eg. In the reaction between H2 and N2 catalysed by Fe catalyst in Haber’s process,
water vapour and O2 acts as temporary poison.
2. Permanent poisoning: In which the catalyst cannot regains its activity even by
removing the poison.
eg. AS2O3 poison permanently the pt powder catalyst in contact process for the
manufacture of SO3 from SO2 and O2
Mechanism of catalytic poisoning:
1. By preferential adsorption of catalytic poison on the surface of solid catalyst.
eg. A monolayer of CO on the Pt surface makes the surface unavailable for further
adsorption of reactants. Thus the rate of reaction decreases.
Pt
Pt
Pt
Pt
Active site = 10
+ CO
O
O
CO
CO
Pt
Pt
Pt
Pt
Active site =6
2. The catalyst combine with chemically with the catalytic poison
eg. Poisoning of iron catalyst by H2S
Fe + H2S → FeS +H2
INHIBITORS: Adsorption of reactants on the surface of catalyst by some ‘foreign’
substance (which does not act as a reactant) on the surface of the catalyst lowering
the “effective area” available for adsorption of reactants. This is turn results in
decrease of the reaction rate. This phenomenon of reducing the reaction rate by the
presence of other substance other than reactants, is known as inhibition and the
substance causing this phenomenon is called inhibitor. In many cases, the inhibitor is a
reaction product.
For example :
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Fe2O3 reduces the catalytic oxidation of naphthalene into phthalic anhydride by adding
V2O5, here V2O5 act as an inhibitor.
ENZYME OR BIOLOGICAL CATALYST:
Enzymes are highly complex, nonliving nitrogenous organic substances produced by
living animals and plants. They possess the capacity in bringing about many complex
chemical reactions like hydrolysis, oxidation, reduction.
ENZYME
SOURCE
ENZYMATIC REACTION
Invertase
yeast
Sucrose→ Glucose + Fructose
Zymase
yeast
Glucose→Ethyl alcohol + O2
Diastase
malt
Starch → Maltose
Urease
soyabeans
Urea→NH3 + CO2
Ptylin
saliva
starch→ sugar
CHARACTERISITCS OF ENZYMES:
1. Enzymes are proteins- i. act as effective catalyst, can speed up the reaction by high
factor 1020 eg. Enzyme carbonic anhydrase (present in red blood cell) catalyses the
reversible reaction of breaking down the carbonic acid to H2O and CO2
H2CO3 → H2O + CO2
ii
catalyst lowers the activation energy
Activation energy
Decomposition of H2O2
without catalyst
18Kcal/ mole
Decomposition of H2O2
reaction goes faster.
with colloidal Pt catalyst
6.3Kcal/ mole , hence
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2.Specificity- Enzyme catalysts are highly specific. A particular enzyme catalyses only
for a particular reaction. For eg.
Urease
NH2CONH2 + H2O
2NH3
Urease
CH3NHCONH2 + H2O
No reaction
3.Maximum efficiency at optimum temperature- The rate of enzyme catalysed
reaction is maximum at optimum temperature. Above this temperature the enzyme gets
denatured, losing its activity. eg. The enzymatic reactions in human body take place
with maximum efficiency at 98.6 oF above this temperature, the enzyme gets
denatured. On the other hand below optimum temperature , the reaction rate is slow
due to temp effects.
4. Maximum efficiency at optimum pH- The rate of enzyme catalysed reaction
generally increases with pH until the optimum pH is reached and then decreases with
further increase of pH . Many of the enzyme catalyzed reaction in human body takes
place at a pH of 7.4.
5.Increase of activity in presence of activators.
The enzymatic activity is enhanced in presence of metal ions (eg. Na+, Cu2+, Co2+, Mn2+)
that get weakly bonded to the enzyme molecules. Similarly coenzyme vitamins
promote the catalytic activity of the enzymes eg. Amylase in presence of NaCl are
catalytically active.
6. Inhibition of activity by poisons: The catalytic activity of enzymes is inhibited or
completely destroyed by the presence of certain inhibitors or poisons, eg. H2S and CS2.
For example, heavy metal ions Hg2+ can react with –SH group of the enzymes and
destroy the enzymatic activity by poisoning.
2 Enz- SH + Hg2+ → 2 Enz- SH -Hg2+ + 2H+
Mechanism of enzyme catalysis: Fischer suggested a Lock and Key mechanism.
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STEP 1: Binding of enzyme (E) to substrate (S) to form an enzyme substrate complex
E +
S → [ ES]
Enzyme substrate complex
STEP 2: Product formation in the complex
[ ES]
→
Enzyme substrate complex
EP
Enzyme product
STEP 3: Release of product from the enzyme
EP
→
Enzyme product
E
+
Enzyme
P
product
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SECTION B
3.WATER AND ITS TREATMENT -1
SOURCES OF WATER:
1. Surface water i Rain water ii,River water iii, lake water iv , Sea water
2.Underground water
IMPURITIES OF WATER: 1. Physical impurities i colour ii turbidity iii taste iv odour
2. Chemical impurities i acidity ii gases iii mineral matters
3. Biological impurities i microorganism ii water bodies
HARDNESS OF WATER: due to presence of Ca, Mg and other heavy metals.
2 C17H35COONa + Ca(HCO3)2
2 C17H35COONa + CaCl2
→ (C17H35COO)2Ca + 2NaHCO3
→ (C17H35COO)2Ca + 2NaCl
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2 C17H35COONa +MgSO4
→ (C17H35COO)2Mg + Na2SO4
Causes of Hardness: Ca and Mg salts
Type of Hardness: 1. Temporary hardness: due to carbonates, bicarbonates and
hydroxides of calcium and magnesium. It can be removed by boling
Ca(HCO3)2 → CaCO3 + H2O + CO2
Mg(HCO3)2 → Mg(OH) 2 + 2CO2
1. Permanent hardness: due to chlorides, sulphates, nitrates of Ca, Mg and sulphates of
Fe, Al. It can be removed by Lime-soda and zeolite process
Alkaline and non alkaline hardness:
Alkaline hardness= temporary= carbonate hardness
Non alkaline hardness= permanent= non carbonate hardness
Expression of hardness as equivalents of calcium carbonate:
Equivalent of CaCO3= [ Mass of hardness producing substance] [equivalent mass of
CaCO3]/ Equivalent mass of hardness producing substances
Equivalent of CaCO3= W X 50/ E
Degree of Hardness:
1 gm mole or 162 gm of Ca(HCO3)2 = 1 gm mole or 100 gm of CaCO3
1 gm mole or 111 gm of CaCl2 = 1 gm mole or 100 gm of CaCO3
1 gm mole or 136 gm of CaSO4 = 1 gm mole or 100 gm of CaCO3
1 gm mole or 136 gm of CaSO4 = 1 gm mole or 100 gm of CaCO3
Temporary hardness = hardness due to Ca(HCO3)2 + hardness due to Mg(HCO3)2
Permanent hardness= hardness due to CaCl2 + hardness due to CaSO4 + due to MgCl2+
due to MgSO4
Total hardness = temporary hardness + permanent hardness
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Unit of Hardness: i Parts per million (ppm) ii Milligrams per litre (mg/L) iii Clark’s
degree (0Cl) iv Degree French (0 Fr)
1ppm= 1mg/l= 0.1 0Fr= 0.07 0Cl= 0.07 grains per gallon
1mg/l =1ppm= 0.1 0Fr= 0.07 0Cl= 0.07 grains per gallon
1 0Fr= 10mg/l =10ppm= 0.7 0Cl= 0.7 grains per gallon
10Cl= 1.43 0Fr= 14.3 mg/l =14.3 ppm= 1 grains per gallon
1 grains per gallon = 1.43 0Fr= 14.3mg/l =14.3ppm= 10Cl
Determination of Hardness: 1. EDTA method 2. Soap solution method 3. O-Hehner’s
method
EDTA method: “Bivalent hardness causing metal ions (e.g. Ca2+ and Mg2+) form
complexes with both Eriochrome Black(EBT) indicator as well as Ethylene Diamine
Tetra Acetic Acid( EDTA) but the EDTA complexes are more stable”
M2+ + EBT
pH= 9-10
M2+=Ca2+ or Mg2+
M2+-EBT
Less stable wine red coloured complex
(metal ion- indicator complex)
M 2+ +
pH = 9-10
EDTA
M 2+ -E D T A
(stable metal ion-EDTA complex)
M 2+ -E B T + E D T A
p H = 9 -1 0
(metal ion- indicator complex)
Wine red colour (less stable)
M 2+-E D T A
+
(metal ion- EDTA complex)
EBT
Free indicator
(more stable)
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Alkalinity of water: Total amount of those substances present in water which
increase the concentration of OH - ions either due to dissociation/ hydrolysis.
Factors:
i Presence of HCO3, HSiO3, SiO32- etc. ions
ii, Presence of salt of weak organic acids
iii, Presence of buffer forming salts
Causes :
i Hydroxides ii carbonates iii bicarbonate iv both hydroxides and carbonates v both
carbonates and bicarbonates , but the combination of OH- and HCO3- is ruled out
because they combine with each other to form carbonate
Type of Alkalinity i Bicarbonate ii, carbonate iii , hydroxide alkalinity
Determination of Alkalinity:
i.
ii.
iii.
OH- + H+ → H2O]P
CO32- + H+ → HCO3- ] P
HCO3- + H+ → H2O + CO2 ]M
Calculation of alkalinity of water by Titrimetric Method
S. Result of titration to Phenolphthalein end point P,
No and methyl orange end point
OH-
CO32-
HCO3-
1
P=0
0
0
M
2
P= M
P= M
0
0
3.
P=1/2 M
0
2P
0
4.
P>1/2 M
2P-M
5.
P<1/2 M
0
2(M-P)
2P
0
M-2P
Boiler feed water: water used for the production of steam in boilers called Boiler feed
water, should be free from dissolved gases like CO2, O2 gases.
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1. Scale and sludge formation in boilers:
i. Sludge formation: Soft, loose slimy ppt, due to MgCO3, MgCl2, CaCl2, MgSO4 etc.
Disadvantage: i poor conductor ii decrease the efficiency
Prevention: i should be well softened ii Blow down operation carried out iii by
scrapping with wire brush
ii. Scale formation: hard, adherent crust formed on inner wall
In low pressure boiler, scales due to Ca(HCO3)2, CaCO3, MgCl2
In high pressure boiler, scales due to CaSO4, CaSiO3, MgSiO3
Causes:
1. Decomposition of CaCO3: Ca(HCO3)2 → CaCO3 + H2O + CO2
CaCO3 → Ca(OH)2 + CO2
Soluble
2. Deposition of CaSO4: CaSO4 soluble in cold water, but solubility decreases with the
rise in temperature. At high temp, CaSO4 pptated, main cause of high pressure boiler.
3. Hydrolysis of magnesium salts: MgCl2 + 2H2O → Mg(OH)2 + 2HCl
Soft type scale
4.Presence of silica: CaSiO3, MgSiO3 soluble in cold water, but completely insoluble in
hot water.
Disadvantage : 1. Wastage of fuel- due to poor conductor of heat. 2. Lowering of boiler
safety- due to overheating, metal become soft and weak, causes distortion of boiler
tube. 3. Decrease in efficiency- due to excessive scale formation in valve and
condenser causes clogging of boiler tube 4. Danger of explosion- thick scales crack due
to uneven expansion, water contact with overheated plates, causes formation of large
amount of steam.
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Prevention: (a) External treatment (b) Internal treatment
(a) External treatment: Lime soda and demineralization process
(b) Internal treatment : addition of chemicals directly to water. Some imp conditioning
methods.
1. Carbonate conditioning: Na2CO3 added, useful for low pressure boiler
CaSO4 + Na2CO3 → CaCO3 + Na2SO4
2. Phosphate conditioning: Suitable for high pressure boiler, Na3PO4 added.
3CaCl2 + 2 Na3PO4 → Ca3(PO4)2 + 6 NaCl
3. Calgon conditioning: addition of calgon (sod.hexametaphosphate)
Na2[Na4(PO3)6
2Na+ + Na4(PO3)6
2CaSO4 + Na2[Na4(PO3)6
Na2[Ca2(PO3)6 ]2- + 2 Na2SO4
4. Colloidal conditioning: colloidal conditioning agents such as glue, agaragar,
tannin, starch.
5. Conditioning with EDTA: complexed with EDTA
Boiler corrosion: The decay of boiler material by its environment is termed
as boiler corrosion.
Factors causing Boiler corrosion
1. Presence of dissolved oxygen: 4Fe + 3O2 + 2xH2O → 2Fe2O3.xH2O (Rust)
2. Presence of dissolved CO2: CO2 + H2O → H2CO3
3. Presence of acid forming salts:
MgCl2 + 2H2O → Mg(OH)2 + 2HCl
CaCl2 + 2H2O → Ca(OH)2 + 2HCl
Fe+ 2HCl → FeCl2 + H2
FeCl2 + 2H2O → Fe(OH)2 + 2HCl
2Fe(OH)2 + O2 → Fe2O3. H2O
PREVENTION:
1. Removal of dissolved oxygen:
2Na2SO3 + O2 →2Na2SO4
Sodium sulphite
Na2S + 2O2 →Na2SO4
Sodium sulphide
N2H4 + O2 → N2 + 2 H2O
Hydrazine
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1. By mechanical deaeration: The dissolved oxygen as well as CO2 can be removed
by this method. The apparatus is called deaerator.
By the addition of alkali- acid can be neutralized.
PRIMING AND FOAMING
Priming: When water is boiled rapidly in a boiler. Steam associated with small droplets
of water called wet steam & the process is called priming.
Causes:
by large amount of dissolved solids such as alkali sulphates and chloride,
by very high water level
high stream velocity and sudden steam which lead to sudden boiling
Prevention:
i, using mechanical steam purifiers
ii, keeping the water level lower
iii, avoiding rapid changes in steam rate
iv, Efficient softening and filtration of boiler feed water
v using a proper design
Foaming: Formation of the persistant foam or bubbles in boiler called foaming.
Causes: caused by the presence of oil and greeze in water. These substances greatly
reduce boiler and cause foaming. The presence of finely divided sludge particles caused
foaming.
Prevention:
i, By removing oil, greeze and finely divided sludge particles from the boiler feed water
ii, by the addition of coagulants such as FeSO4, sodium aluminate
iii, adding antifoaming chemicals such as castor oil.
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Caustic embrittlement: When boiler operates at high pressure and boiler feed
water contain Na2CO3 as an impurity. At high pressure Na2CO3 undergo hydrolysis to
form NaOH
Na2CO3 + H2O → 2NaOH + CO2
Formation of NaOH makes the boiler water caustic. The caustic water flows into the
minute hair cracks by capillary action. Here water evaporates and con of NaOH
increases. The highly conc NaOH dissolves the iron of boiler as sodium ferroate or
hypoferrite Na2FeO2.
2NaOH + Fe → Na2FeO2 + H2
This causes the formation of irregular intergranular cracks on the boiler metal at places
of high local stress such as bends, joints, rivets. Caustic embrittlement is a localized
phenomenon. The conc cell set up which can be expressed as shown below
Iron at the point of high
conc NaOH
dilute NaOH
iron at the
surface local stress eg. Rivets
(Anode)
(cathode)
Prevention:
1. Water should be softened by sodium phosphate instead of Na2CO3.
2. Tannin or lignin should should be added to the boiler water because these blocks
the hair cracks inside the boiler.
3. Using Na2SO4 to the boiler water. Conc of Na2SO4 to NaOH is 1:1, 2:1: 3:1 in
boilers working smoothly at 10, 20 and greater than 20 boiler.
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4.WATER AND ITS TREATMENT -2
Treatment of water for domestic use:
Requisites of Drinking water:
1.
2.
3.
4.
It should be clear, colorless and odourless.
It should have an agreeable taste.
It should be free from pathogenic microorganisms.
It should be free from dissolved gases such as H2S, harmful minerals such as lead,
arsenic chromium salt and mineral oil.
5. Its alkalinity should not be high. pH should be in the range 7-8.5
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6. It should neither too hard nor to soft. The recommmened hardness is about 300
mg/L as CaCO3 equivalent.
7. The total dissolved solids should be less than 500 ppm.
Various process for the treatment of water :
1.
2.
3.
4.
5.
Screening
Sedimentation
Coagulation
Filtration
Sterilization (Disinfection )- (a)by Boiling (b) Aeration(c) by UV rays(d) by
Bleaching powder (e) by Chlorination (f) by Chloramines, superchlorination,
Break point chlorination, Dechlorination(g) by ozone
6. Desalinationi, Reverse osmosis
ii Electrodialysis
7. Softenning of water (Removing of the dissolved salt) i, Lime soda process (a) cold (b) Hot
ii Zeolite
iii Demineralization- (a) Ion exchange (b) Mixed bed demineralization
Removal of the suspended impurities: suspended impurities (inorganic & organic) in
water can be removed by the screening
1. Screening: process of removing of floating material eg. Wood pieces, leaves from
the water. Raw water is allowed to pass through a screen having large number of
perforations which removes the large and small floating matter.
2. Sedimentation: The process of water to stand undisturbed for sometime in order to
settling down the suspended particles under the action of gravity is called
sedimentation. The water obtained on screenings is taken into the large tanks and it
allowed to stand for few hours or even days, suspended particle settle down at the
bottom. It requires large capacity settling tanks. Plain sedimentation usually
removes 70-75% of the suspended matter. The process of sedimentation is
generally carried out in continuous flow type tanks in which water flows
continuously in a horizontal, radial, vertical flow tanks.
3. Coagulation: When water contains finely divided silica, fine clay particles and other
impurities present in the colloidal form, plain sedimentation does not remove these
impurities as these impurities do not settle down easily. In such case it is necessary
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to coagulate the colloidal impurities by the addition of certain chemicals called
coagulation
Coagulation are certain chemicals which provide ions of opposite charge. These
externally added ions neutralize the charge on colloidal particles and help them to grow
in size and finally to settle them down. This process is known as coagulation.
1.Aluminium sulphate: most common coagulating agent used either as filter alum
[Al2(SO4)3 or as alum [k2SO4. Al2(SO4)3.24 H2O]. It hydrolyses in water to form Al(OH)3
which act as a coagulant.
[Al2(SO4)3 + 6H2O→ 2 Al(OH)3 + 3H2SO4
If water possesses no alkalinity alkali such as Na2CO3 or Ca(OH)2 is added
[Al2(SO4)3 + 3Na2CO3 + 3H2O→ 2 Al(OH)3 + 3Na2SO4 + 3CO2
2.Sodium aluminate: It is used along with Al2(SO4)3 for the treatment of acidic waters. 6
NaAlO2 + Al2(SO4)3 + 12 H2O → 8 Al(OH)3 + 3Na2SO4
3.Ferrous sulphate: It is used for the treatment of slightly alkaline water.
FeSO4 + 2H2O → Fe(OH)2 + H2SO4
4Fe(OH)2 + 2H2O + O2
→ 4Fe(OH)3
4.Filtration: It is the process of removal of coarse impurities (eg. Coagulated/ insoluble
colloidal material, suspended matter) some of the microorganism by passing water
through a porous material consisting of a bed of fine sand and other granular materials.
The porous material used is called filtering medium and equipment used for filtration is
called a filter
The filter used for the treatment are of 2 types
I gravity type filters- (a) slow sand filter (b) rapid sand filters
i, pressure type filters
Gravity Sand filter: Filtering medium consist of three layers
Top layer- fine sand (thick), middle layer- coarse sand, bottom layer- gravels. The filter is
provided with an inlet for water and underdrain channel at the bottom for the exit of
filtered water. This filter are used where a large quantity of water is tobe filtered. The
rate of filtration is slow and very fine sand particles are used, a large portion of
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bacteriological impurities are removed such sand filter are best suited for municipal
water.
Pressure filters: Pressure filters are used for small scale supplies for eg. Industrial
plants. A typical pressure filter consist of a cylindrical steel shell containing three layers
of filtering media I, Pebbles (10-25 mm grain size) ii Coarse sand (5-7 mm grain size) iii
fine sand (1-2 mm grain size)
Alum + water → slimy layer of Al(OH)3
Colloidal and bacteriological impurities are removed.
5.Sterilization of water (removal of bacteria and microorganism):
The filter water still contain small amount of pathogenic bacteria like salmonella , vibrio,
coliform In order to use this water for drinking purpose, all the pathogenic bacteria
must be killed. “ The process of destroying/ killing of pathogenic bacteria and the other
microorganism called disinfection and the chemical used is called disinfectants”
(a) Boiling: good method, it takes 15-20 minutes destroys all the diseases causing
bacteria. This method is useful only for household purposes during epidemic like cholera
Limitations: 1. Costly
2 kills only microorganism existing at the time of boiling. It does not protect water
against any possible future infection.
3. The taste of water may change on boiling.
(a) Aeration: The process of spraying water in the form of fine droplets into the
atmosphere is known as aeration (absorbed O2 and remove CO2). water is forced
under pressure through a perforated pipe. As water sprays into the air, it comes in
contact with O2 of air and UV rays of the sun. It helps in killing bacteria to certain
extent
(b) Sterilization by UV rays: Although sunlight is also helpful in killing bacteria, it cannot
penetrate large depths of water hence it is not an efficient method for the
sterilization of water. UV rays destroys bacteria quite effectively. When water is
exposed to UV raysfrom an electric mercury lamp immersed in the water, most of
the pathogenic bacteria are destroyed
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Advantage i It does not require any chemical ii it has not any bad effect during
treatment iii it does not produce any odour in water iv, it takes very small time
(c) Sterilization by bleaching powder: It contains 30% available chlorine.
+ Cl2
CaOCl2 + H2O → Ca(OH)2
Cl2 + H2O →
HOCl
+ HCl
Hypochlorous acid
HOCl
→
HCl + [O]
Bleaching powder should be used only in calculated amount because it will give bad
taste and unpleasant odour while lesser amount of it will not sterilize the water
completely
Disadvantages: 1. It is stable during storage
2.In introduces calcium in water. The percentage of Ca in water increases and water
becomes hard
3.When used in excess, it produce unpleasant odour in water. Too much excess may
cause irritation to mucous membranes .
(d) Sterilization by chlorine (chlorination) : It can be used directly as a gas or as
chlorine water. It react with water to form hypochlorous acid and nascent oxygen
both are powerful germicide.
→
HOCl + HCl
Cl2 + H2O
HOCl
→
HCl + [O]
The nascent oxygen destroys harmful germs and bacteria by disinfectants as they are
capable of rupturing the cell
Advantages: 1. Does not decompose on standing and can be stored in a very little
space.2.Can be obtained in pure form 3. more effective and economical 4. Can be
used at high as well as low temperature 5. No impurity is introduced into the water
Process: Water is treated with chlorine in tower known as chlorinator provided with a
number of buffle trays. Cl2 and water are introduced at the top. During their passage
through tower, they get thoroughly mixed, the treated water is taken out from the
bottom.
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(f)Sterilization by chloramine: NH3 and Cl2 when mixed in ratio 1:2 by volume
produced compound known as chloramines
NH3 + Cl2 → Cl NH2 + HCl.
It is a stable compd and doesn’t impart any disagreeable smell or bad taste to water
Cl NH2 + H2O → HOCl + NH3
HOCl
→
HCl + [O]
Superchlorination: sometime the quality of raw water may be uncertain. There are
situation where the presence of resistant microorganism may be suspected. In these
cases addition of chlorine in excess amount may be required for a given period of
contact time. This type of chlorination is referred to as superchlorination.
Sterilization process involve a large excess of chlorine is called superchlorination.
Superchlorination not only destroys the microorganism but also the other organic
impurities present in water. The process is followed by dechlorination by NH3 or SO2.
Break-point chlorination: refers to chlorination of water till all NH3 is converted into
NCl3 or N2, it determines whether chlorine is further added or not. Breakpoint
chlorination is a controlled chlorination process in which water is treated with an
amount of chlorine which is sufficient to
1. destroy bacteria
2. to oxidize organic matter
3. to oxidise the ammonia, if present in water
4. leave behind slight excess of free chlorine which could act as disinfectant during
storage of water.
Curve I – OL - Distilled water – applied chlorine is increased, the amount of residual
chorine increases
Curve II– ABCD - Impure water
OA-When the dose of applied chlorine is low, all the added chlorine get consumed
in complete oxidation of reducing substances present in water, hence no free
residual chlorine.
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AB- On increasing the amount of added chlorine, the amount of residual chlorine is
also increased slowly- correspond to the formation of chloro-organic compound
without oxidizing them.
At high dose or conc. of applied chlorine, oxidation of chloro-organic compound or
microorganism takes place. Hence the amount of residual chlorine is decreased.
BC- The destruction of chloro-organic compound and chloramines takes place
continuously and reaches the minima.
NH2Cl + 3Cl2 + H2O
→ N2 + N2O + 10 HCl
2NHCl2 + 3Cl2 + 4H2O → 2NO2 + 10 HCl
Point C - after reaching the minima, the added chlorine does not take part in
chemical reaction.
Curve CD - the amount of residual chlorine is increased by adding the amount of
chlorine
Point C- Break point chlorination- at which free residual chlorine begins to appear
Hence for effectively killing the microorganism, sufficient amount of chlorine must be
added. After break point chlorination all the bacteria killed, oxidizing organic matter but
it produced eliminating bad taste and disagreeable odour in water.
Advantages and significance:
1.
2.
3.
4.
5.
It indicates the complete destruction of organic compound.
It completely destroys all the pathogenic bacteria
It helps to calculate the sufficient amount of chlorine for adding in water.
It prevents the growth of any weeds in water.
It also signifies the complete decomposition of NH3, removal of coloring materials
and improvements of taste and odour of the water sample.
Dechlorination: The water treated by break point chlorination contains decomposition
product formed and may contain excess of chlorine. These product may be removed by
the process known as dechlorination. These decomposition product may be removed by
filtering the treated water over activated carbon. Overchlorination can also be removed
by excess chlorine with SO2 or Na2SO3.
SO2 + Cl2 + 2H2O → 2HCl + H2SO4
Na2SO3 + Cl2 + H2O → 2HCl + Na2SO4
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Sterilization with ozone: ozone is unstable compound and decomposes to molecular
oxygen and nascent oxygen.
O3 → O2 + O
The nascent oxygen released is very effective and kills all the germs and bacteria. During
ozone sterilization, ozone is injected through an injector into the water in a contact
tank. Sterilized water is collected from the top.
The commonly used dose strength of ozone for the sterilization of water is 2-3 ppm.
Advantages:
1. Ozone act not only as a sterlizing agent but also as a bleaching, decolorizing and
deodourising agent.
2. It improves the taste of water and actually produces a very palatable taste.
3. Its excess is not harmful since it is unstable and decomposes into oxygen.
6. Desalination: process of removal of dissolved salt (particularly NaCl) from the
water is called desalination. Salinity expressed in mg/L of the dissolved salt. On the
basis of salinity water graded
Salinity
1.Fresh water
less than 1000 mg/l
2. Brackish water
1000-35000 mg/l
3. Sea water
greater than 35000 mg/l
Two method of desalination
(A)Reverse osmosis (B) Electrodialysis
(A) Reverse osmosis: spontaneous process, “ the flow of solvent from the conc.
solution to dilute soln are separated by a semi permeable membrane when a
pressure greater than the osmotic pressure is applied on the more concentrated
solution side, the solvent is forced to move from the the more conc. soln to dilute
soln . This phenomenon is called reverse osmosis.
Principle: useful for the desalination of brackish or sea water. Brackish water or sea
water contain many dissolved salts and is more conc as compared to fresh water. If sea
water kept in contact with fresh water through semi permeable and pressure of order
15-40 kg/cm2 is applied on sea water, reverse osmosis will and water will be forced to
flow from sea water to fresh water side leaving behind the dissolved salt.
Process: Desalination of sea water/ brackish water is carried out in a reverse osmosis
cell. In this cell saline water is separated from the fresh water through semi permeable
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membrane made of very thin films of cellulose acetate affixed to side of a perforated
plate or tube, pressure of the order 15-40 kg/ cm2 is applied to sea water. Reverse
osmosis take place.
Advantage: 1. The process removes ionic as well as nonionic dissolved salt. It is also
effective in removing colloidal impurities.
1. The process involves a very low capital and operating cost. It is suitable for
converting sea water into drinking water
2. The water obtained by his process may be used in high pressure boilers
3. It removes colloidal silica which is not removed by demineralization.
(B) Electrodialysis:
Principle: involves separation of dissolved salt from the saline water in the forms of ions
under the influence of direct current using particular types of membrane called ionselective membrane. An ion selective membrane is permeable only one kind of specific
charge. For eg. Cation selective membrane allows the passage of cations only. Similarly
an anion selective membrane is permeable only to anions. When direct current pass
through it enclosed between ion selective membrane, the cations of the dissolved salt
move towards cathode through cation selective membrane whereas anions of the salt
move towards through anion selective membrane, result decrease the conc. of the ions
in saline condition.
The process: The process is carried out in a special type of cell called electrodialysis
cell. It consist of large no. of paired sets of ion selective membranes.
Saline water under a pressure of about 5-6 kg/m2 is introduced from the top of the
cell where it passes between membrane pairs.
An electric field is applied perpendicular to the direction of flow of water. The ions
start moving towards the oppositely charged electrodes through the membranes.
The conc of ions in alternate compartments 2,4,6 decreases, while the conc. of
ions in alternate compartment 1,3,5,7 goes on increasing. Thus water collected
from the compartment 2,4,6 is pure while that collected from compartment 1,3,5,7
is impure.
7. Softenning of water (Removing of the dissolved salt) –The process of removing the
hardness causing salts from the water called softening of water.
1, Lime- soda process :
Principle : Conversion of all the soluble hardness causing salts into insoluble precipitate
by the addition of soda and lime which can be easily removed by settling and filtration
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water to be softened is treated with calculated amounts of lime ca(OH)2 and soda
Na2CO3.
Function of lime: lime removes temporary Ca and Mg hardness, permanent Mg, Al, Fe
hardness and dissolved CO2 and H2S gases and free mineral acid present in water. Lime
does not react with CaCl2 and CaSO4 so it cannot remove calcium permanent hardness.
(a) Removal of temporary, calcium and magnesium hardness:
Ca(HCO3)2 + Ca(OH)2 → 2 CaCO3 + 2H2O
Mg(HCO3)2 + 2Ca(OH)2 → 2 CaCO3 +Mg(OH)2 + 2H2O
(b) Removal of permanent magnesium hardness:
MgCl2 + 2Ca(OH)2 → CaCl2 +Mg(OH)2
MgSO4 + Ca(OH)2 → CaSO4 +Mg(OH)2
(c) Removal of dissolved iron , aluminium salts:
FeSO4 + Ca(OH)2 → CaSO4 + Fe (OH)2
H2O+ 2Fe (OH)2 + ½ O2 → 2Fe (OH)3
Al2(SO4)3 + 3 Ca(OH)2 → 3CaSO4 + 2Al (OH)3
(d) Removal of dissolved CO2 and H2S:
CO2 + Ca(OH)2 → CaCO3 + H2O
H2S + Ca(OH)2 → CaS
+ 2H2O
Function of soda:
CaCl2 + Na2CO3→ 2 NaCl + CaCO3
CaSO4 + Na2CO3→ Na2SO4 + CaCO3
(a)Cold lime soda process: can be carried at room temperature
water + soda + lime + coagulant → insoluble ppt (in the form of sludge seTle down &
taken out through outlet at the bottom) →soUened water (filtered by wood fibre)&
taken out from an outlet provided at the top
The softened water contain residual hardness of about 50-60 ppm.
(b) Hot lime soda process:
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Water + softening chemicals → 94-1000
Method: Lime soda softening plant consists of 1. Reaction tank 2. Conical
sedimentation vessel 3. Sand filter
Raw water + softening chemicals+ agitated with superheated steam → Rxn takes place,
softened water filtered by sand filter which is taken out at the bottom and precipitated
sludge is taken out through an outlet provided at the bottom.
The softened water contain residual hardness of about 15-30 ppm.
Advantage:
1.
2.
3.
4.
5.
6.
7.
Filtration much easier as the viscosity of water becomes low.
HLS process is much faster as compared to CLS process.
Lesser amount of coagulant needed because precipitated sludge forms rapidly.
Process increases pH value of treated water reducing corrosion of distribution pipes.
Fe & Mn are also removed from the water
Much of the dissolved gases in water also removed.
Due to an increase in pH, the amount of pathogenic bacteria in treated water also
gets reduced.
8. Residual hardness is far less than the cold process.
Disadvantages:
1. Disposal of large amounts of sludge formed in the process poses problems.
2. The treated water obtained by this process is not completely softened. It still
contains hardness 15-30 ppm which is not good for the boilers.
2 .Zeolite process( Permutit process):
Ion exchange technique, used for softenning of water. This process makes use of certain
complex inorganic salt called zeolite which possesses property of exchanging the
hardness producing ions such as Ca2+, Mg2+ with those ions which do not causes
hardness Na+ ions.
Permutit or zeolite(found in volcanic rocks) is sodium-aluminium orthosilicate
Na2Al2Si2O8.x H2O Na2Ze where Ze= Al2Si2O8.x H2O
1. Natural zeolite: Non porous & amorphous
eg. Natrolite: Na2OAl2 O3 3 SiO2.2 H2O ,
H2O
Laumontite: Na2OAl2 O3 3 SiO2.2
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2. Synthetic zeolite: porous and possess gel structure, possess high exchange capacity
as compared to natural zeolite
Sodium zeolite/ permutit - Na2OAl2 O3 x SiO2.y H2O where x = 2-10, y = 2-6
They are prepared by heating sodium silicate, Al2(SO4)3, NaAlO2
Process: Zeolite loosly packed over a layer of coarse sand in tank. Hard water is allowed
to percolate through it. As the hard water percolates through the permutit, the ca2+ and
Mg2+ present in water gets replaced by the action of sodium zeolite.
Ca(HCO3)2 + Na2Z
Mg(HCO3)2 + Na2Z
CaSO4
+ Na2Z
MgSO4
+ Na2Z
CaCl2
+ Na2Z
MgCl2
+ Na2Z
→ CaZ + 2 NaHCO3
→ MgZ+ 2 NaHCO3
→ CaZ +Na2SO4
→ CaZ + Na2SO4
→ CaZ + 2NaCl
→ MgZ +2NaCl
Regeneration of Zeolites: This process removes both temporary& permanent hardness.
when permutit is completely converted into Ca and Mg zeolites, it gets exhausted and
regenerated. The regeneration of zeolote is done by percolating a 10% brine (NaCl soln)
through the exhausted zeolite.
CaZ + 2NaCl → CaCl2 + Na2Z
MgZ +2NaCl → MgCl2 + Na2Z
Limitations:
Water containing turbidity and suspended impurities can not be treated by this method
because turbidity clogs the pores of zeolite bed, hence water fed into plant should be
free from turbidity and suspended matter.
1. The process exchange only Ca2+, Mg2+ ions with Na + ions, doesn’t remove CO32-,
HCO32-. These acidic ions not suitable for boiler as it causes corrosion of boiler.
2. The process not efficient for Fe2+, Mn2+ as these ions convert sodium zeolite into
their respective zeolite which are difficult to be regenerated.
3. Excess acidity or alkalinity can’t be treated by this method because highly acidic or
alkaline water decompose sodium zeolite.
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Advantage:
1. process removes hardness completely, softened water contains hardness about 10
ppm
2. Equipment compact and doesn’t occupy much space
3. Process doesn’t involve formation of any ppt, process is free from the problem of
sludge formation and after precipitation
4. Process doesn’t involve formation of any ppt, free from the problem of sludge
formation.
3.Demineralization process:
“complete removal of all hardness producing ions present in water. The process
produced deionized water of very high purity”
1.Ion exchange process: The ions present in water are removed by some complex
organic compounds known as Resins. Resin acts as ion -exchangers and remove all
minerals from hard water. They remove cations and anions (except H+ and OH- ions)
from the water and make it completely demineralised.
Two types of resin
i Cation exchange resins : cation exchange resin present in hardwater with H+ ions.
They possess acidic groups such as –COOH or –SO3H gps represented as resin-H+
eg. Carboxylated or sulphonated styrene-divinylbenzene copolymers.
ii Anion exchange resins : Anion exchange resin present in hardwater with OH- ions.
They possess basic groups such as -OH or –NH2 gps represented as resin-OHeg. styrene-divinylbenzene or amino formaldehyde copolymers.
Process: Apparatus consist of 2 containers containing cation exchange resin and other
anion exchange resin over a bed of gravel.
Hard water first passed through cation exchange resin and then anion exchange.
The reactions takes place
Ca2+ + 2 resin-H+ → Ca(resin)2 + 2H+
Mg2+ + 2 resin-H+ → Mg(resin)2 + 2H+
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SO42- + 2resin-OH-- → ( resin)2- SO42- + 2OHH+ + OH- → H2O
Regeneration: Cation and anion exchange resin are regenerated by passing moderately
H2SO4/ HCl and NaOH respectively.
Ca(resin)2 + 2HCl → 2 resin-H+ + CaCl2
Mg(resin)2+ 2HCl → 2 resin-H+ + MgCl2
resin-Cl+ NaOH- → resin-OH- + NaCl
2(resin)2SO4 + 2NaOH- → 2resin-OH- + Na2SO4
Advantage: 1. Water of low hardness 2 ppm is produced
Highly alkaline/highly acidic water can be softened.
Limitations: 1. Equipment costly
2.Turbid water decreases the efficiency of resin
2. Mixed bed Dimineralization process:
mixed bed of cationic and anionic resin is taken in single vessel
water is passed through mixed bed, it comes in contact with two type of resins
several times.
Production of deionized water having less than 1ppm of dissolved ions
When resin exhausted, mixed bed backwashed. Cation and anion exchange resin
regenerated with NaOH and dil H2SO4 respectively.
Advantage: 1. Very low hardness water
2.can be used for acidic and alkaline water.
Disdvantage: 1. Equipment costly
2.If turbid water used then exchangers become clogged.
SECTION C
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5.CORROSION AND ITS PREVENTION
Corrosion: “The gradual disintegration or deterioration or destruction of the metal
by chemical or electrochemical environment is called corrosion.”
eg. 1. Rusting of iron (when a piece of iron is exposed to atmosphere, a reddish brown
coating of iron oxide is deposited)
2. Gold which is highly resistant to corrosion get readily corroded when exposed to an
atmosphere of mercury.
3. When Cu exposed to air containing CO2, a green thin film of basic carbonate.
Causes: Most of the metals occur in nature in combined state in the form of oxides,
sulphides, sulphates, carbonate. Only a few noble metal like Au, Pt occur in nature in the
free state.
corrosion(oxidation) Metallic compound
Pure metals
(high energy)
Metallurgy(Reduction)
(lower energy)
+ Energy
Thermodynamically
stable
Thermodynamic
unstable
Different type of corrosion:
1. Dry corrosion (chemical) – i, oxidation corrosion ii corrosion by other gases iii
2.
3.
4.
5.
6.
liquid metal corrosion
Wet corrosion (electrochemical)
Galvanic corrosion
Pitting corrosion
Differential corrosion
Stress corrosion
1. Dry corrosion (chemical corrosion): caused by direct chemical action of atmospheric
gases such as O2, SO2, H2S, halogens or anhydrous liquids on metal called chemical or dry
corrosion.
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i.Oxidation corrosion:
corrosion occurs through direct action of oxygen on metal in the absence of
moisture, occurs at ordinary temp.
eg. Alkali metals (Li, Na, K) and alkaline earth metals(Be, Mg, Ca) get oxidized at ordinary
temp & corroded.
Mechanism: when metal is exposed to air, absorption of oxygen takes place at ordinary
temp., absorption is physical in nature and is due to vander Waals forces. The absorbed
oxygen react with the metal by electron transfer between metal atoms
2M → 2Mn+ + 2ne- loss of e-s by metal
Metal atom
nO2 + 2ne- → 2nO2- gain of e-s by metal
______________________
2M + nO2 → 2Mn+ + 2nO2Metal ion
oxide ion
Due to electron transfer reaction, a metal oxide scale is formed at metal surface. This
scale act as barrier and prevent the underlying metal atoms to come in contact with the
oxygen
1.The metal diffuse outwards through the scale at the surface.
2. Oxygen diffuses inwards through the scale to underlying metal, the outward diffusion
of the metal is faster than the inward diffusion of oxygen because metal ions is smaller
than oxygen ion so metal surface is covered with the monolayer of oxide film
Corrosion depends upon the nature of the oxide film
1. Oxide film is stable or non porous: it cut off the penetration of oxygen to
underlying metal and act as a protective coating, prevents the further corrosion of
metal. Stable oxide film is formed in case of Al, Sn, Pb, Cu, Pt etc.
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2. Oxide film is unstable : it decomposes back into oxygen and metal eg. Ag,Au,Pt
Metal
Metal oxide
+ Oxygen
3. Oxide film is volatile : The oxide layer volatilizes as soon as it is formed, the
underlying metal get exposed to further attack, causes rapid and continuous
corrosion. eg. Mo
Mo + 3O2 → 2MoO3
2
4. Oxide film is porous: The atmospheric oxygen can penetrate inward easily and can
attack the underlying metal. Corrosion will continue unobstructed and entire metal gets
completely converted into oxide. eg. Alkali and alkaline earth metal
Pilling-Bedworth ratio: “When the volume of the oxide is greater than the volume of
metal then the oxide layer is tightly adherent, nonporous, and protective eg. Aluminium
oxide, lead oxide, tin oxide. If the volume of oxide of oxide is less than the volume of the
metal, the oxide layer is porous, non continuous, non protective eg. Alkali & Alkailne
earth metal”.
ii.(a) Corrosion by other gases: caused by CO2, SO2,H2S,F2,Cl2
eg. 1. Attack of Cl2 on Ag →AgCl film (non porous)
2Ag + Cl2 → 2AgCl
2.Attack of dry Cl2 on Sn → SnCl4 film(volatile)
Sn + 2Cl2 → SnCl4
3.Attack of H2S on steel(petroleum industry) → FeS scale
H2S + Fe →FeS + H2
(b)Corrosion by hydrogen:
When metal is exposed to hydrogen environment, H2 diffuses into metal lattice in
the form of atoms & collects in interstitial spaces.
Further diffusion helps hydrogen atom to combine together to form H2 gas. This
develops pressure inside the lattice and causes cracking or blistering of metal or
hydrogen embrittlement. Due to this metal becomes weak.
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for eg. Aq soln of H2S reacts with iron surface.
Fe + H2S → FeS + 2H
Scale(porous)
Atomic hydrogen reacts with C, S, N, O forming atmospheric gases.
iii. Liquid metal corrosion: When liquid metal is made to flow at high temp over a solid
metal or alloy, the solid metal or alloy usually gets weakened. This type of corrosion
called Liquid metal corrosion. eg. - Cd in nuclear energy devices .
2.Wet corrosion(electrochemical): “Flow of e-s from anodic area to cathodic area
through a conducting solution called wet corrosion”
i.
ii.
when conducting liquid containing varying amount of oxygen is in contact
with metal
when two diff metal are in contact with each other in presence of an aqueous
solution.
At anode - metals undergo oxidation
At cathode - reduction to form nonmetallic ions such as O2-, OHRusting of iron: The phenomenon of deposition of reddish brown coating on the surface
of iron by the action of moist air called rusting and reddish brown coating called rust.
4Fe(s) + 2xH2O+ 3O2(g) → 2Fe2O3.xH2O (s)
hydrated ferric oxide (rust) soft& porous
Factors which governs rusting:
1.
2.
3.
4.
Presence of air
Presence of moisture
Presence of CO2
Presence of impurities of less electropositive metals in iron
ELECTROCHEMICAL THEORY OF CORROSION: corrosion is basically an electrochemical
phenomenon. It is mainly due to a difference in the electrochemical behavior of
different parts of the surface of the metal.
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Mechanism of rusting of iron: The chemically non uniform parts of iron surface act as
miniature galvanic cells in the presence of water containing dissolved oxygen and CO2.
One part- cathode, other part-anode, e-s flow from anode to cathode.
In the anodic area: Fe(s) → Fe2+(aq) +2e- ; E0Fe2+/Fe = -0.44 V oxidation
The electrons to cathodic area, In the cathodic area electrons reduce the oxygen in the
presence of H+ ions. The H+ formed in the water film due to dissociation of H2CO3 which
is formrd due to dissolution of CO2 in water.
In water film:
H2O(l) + CO2(g) → H2CO3(aq)
H2CO3 (aq)
H+ (aq) + HCO3-(aq)
In the cathodic area: O2(g) + 4H+ (aq) + 4e- → 2H2O(l); E0= 1.23 V
The overall reaction
At anode
: Fe(s) → Fe2+(aq) +2e-
At cathode
: O2(g) + 4H+ (aq) + 4e- → 2H2O(l)
The overall reaction in a
miniature cell
2Fe(s) + O2(g) + 4H+ (aq)
]x 2
2 Fe2+(aq) + 2H2O(l); E0 cell= 1.67V
Fe2+ ions move through water on the surface of the iron object. Fe2+ oxidized to Fe3+ by
atmospheric oxygen and moisture to form hydrated iron(III) oxide Fe2O3. xH2O(l).
4Fe2+(aq ) + 4H2O(l)+ O2(g) → 2Fe2O3 (s) + 8H+
Fe2O3 (s) + xH2O(l)
Fe2O3. xH2O(l)
hydrated ferric oxide (rust) soft& porous
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H+ ions produced in the reaction again utilized in the process of rusting. The process
accelerated in the presence of impurities of less electropositive metals because
impurities set up a number of miniature galvanic cells on the surface of iron.
3.Galvanic corrosion: “When two different metals either in direct contact or connected
through an electrical conductor are exposed to a conducting solution. The less noble
metal having lower value of standard reduction potential or placed higher in the
electrochemical series gats corroded.”
For example, Zn (E0 = -0.76V) is less noble than Cu (E0 = +0.34V) as the Zn is placed
higher in the electrochemical series, so Zn being less noble undergoes corrosion,
whereas Cu being more noble remains protected.
Mechanism: The galvanic corrosion is due to difference in the electrode potentials.
The less noble metal- anode, more noble metal- cathode, thus galvanic cell occurs and
e-s flow from the anode to the cathode. For eg. Zn & Cu, Zn act as anode while Cu act as
cathode.
Zn → Zn2+ +2eThe electrons migrate to more noble Cu electrode and Zn2+ ions pass into the solution,
Zn corroded.
This corrosion depends on the two factors
i.Potential difference between the metals: Larger the potential diff between the two
metals, greater is the extent of corrosion
ii. Area of the more noble metal: Area of noble metal more than less noble metal, the
process is rapid.
4. Pitting Corrosion: The breakdown or cracking of the protective film on a metal at
specific points is called pitting.
Mechanism: Pitting corrosion is due to heterogeneity in metal surface and results
formation of holes and pits in metal. When protective surface film gets cracked at
certain points in presence of suitable environment, the anodic and cathodic area are
formed.
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Cracking occurs due to
1. Surface roughness
2. Development of scratches
3. Local strains
4. Turbulent flow of soln over the metal
5. Chemical attack
Prevention: 1. Use of pure metals devoid of any impurities
1. Proper designing of metal structures
2. Proper polishing of metal surface
5.Differential aeration corrosion:
Mechanism: “when one part of metal is in contact with air of particular conc. And some
other part of diff conc. a potential diff between the differently aerated areas exits due to
formation of oxygen concentration cells. The part of the metal in contact with air having
low oxygen concentration or poor oxygenated part act as anode .The part of the metal
in contact with air having high oxygen concentration or rich oxygenated part act as
cathode”.
Example: 1. A zinc rod is partially immersed in a dilute solution of NaCl electrolyte
At anode
: Zn→ Zn2+ +2e-
At cathode
: ½ O2+ H2O + 2e- → 2OH-
The overall reaction
: Zn + ½ O2 + H2O → Zn2+ + 2OHZn2+ + 2OH- →Zn(OH)2
Example: 2. A part of piece of iron metal is covered with dirt and metal in contact with air.
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Part without dust
_
-
(rich oxygenated part) - cathode- ½ O2+ H2O + 2e- → 2OH
Fe + ½ O2 + H2O → Fe2+ + 2OHFe2+ + 2OH- →Fe(OH)2
The overall reaction
Prevention: 1. Metal surface needs to be cleared from time to time .
2.Crevices and cracks should not be allowed.
6.Stress Corrosion: “The corrosion of a metal or an alloy caused by the combined action of
tensile stress and the corroding environment is called stress corrosion”
This type of corrosion may cause the cracking of the metal or alloy. It is referred to as stress
cracking.
Factors responsible for stress corrosion:
1.Tensile stress: caused by welding, thermal treatment, heavy working like rolling, drawing
residual cold working , quenching & Insufficient annealing
2.Corroding environment:
Corrosive agent -1. NaOH & strong nitrate soln for mild steel
2Traces of ammonia for brass 3. Acid chloride soln for stainless steel
Mechanism:
1. It occurs through electrochemical phenomena
2. Alloys having internal stresses due to metallurgical operations are more susceptible to stress
corrosion/stress cracking.
3. Stress part- anode, unstressed part- cathode, the anodic part undergo corrosion.
Types of stress corrosion: 1. Season cracking- refers to stress corrosion of copper alloys
particularly brass. Brasses are binary alloy of Cu and Zn, both form stable complex ions
[Cu(NH3)4]2+, [Zn(NH3)4]2+ causes fissures.
2.Caustic embrittlement: When boiler operates at high pressure and boiler feed water
contain Na2CO3 as an impurity. At high pressure Na2CO3 undergo hydrolysis to form
NaOH
Na2CO3 + H2O → 2NaOH + CO2
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Formation of NaOH makes the boiler water caustic. The caustic water flows into the
minute hair cracks by capillary action. Here water evaporates and con of NaOH
increases. The highly conc NaOH dissolves the iron of boiler as sodium ferroate or
hypoferrite Na2FeO2.
2NaOH + Fe → Na2FeO2 + H2
This causes the formation of irregular intergranular cracks on the boiler metal at places
of high local stress such as bends, joints, rivets. Caustic embrittlement is a localized
phenomenon. The conc cell set up which can be expressed as shown below
Iron at the point of high
conc NaOH
dilute NaOH
iron at the
surface local stress eg. Rivets
(Anode)
(cathode)
3.Corrosion fatigue: occurs due to repeated cyclic stresses caused by shaking,
vibration, tapping, flexing in presence of corrosive environment when stress is below
threshold limit.
Factors affecting corrosion: (A) Nature of the metal (B) Nature of the environment
(A)Nature of the metal :
1.Position in galvanic series: “Higher the position of metal in the series, more its
activity and greater is its tendency to undergo corrosion”.
More active metal – anode & larger the diff in position of two metals in galvanic serieshigher is rate of corrosion of more active metal.
2.Overvoltage : “The diff between the voltage required for an electrode reaction to
occur and that expected theoretically is referred to as overvoltage. “
Anodic metal having small overvoltage corrodes much faster as compard to that
having a higher overvoltage.
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For example: when Zn is placed in 1N H2SO4 , the rate of rxn is slow due to high
overvoltage( 0.70 V) inspite of high activity of Zn. On addition of CuSO4 , the rate of
reaction become fast due to small overvoltage( 0.33 V) forming minute cathodes .
3.Relative area of the cathodic to anodic parts: Rate of corrosion increases with
increase in ratio of cathodic to anodic part.
e.g. Small steel pipe fitted in large Cu tank undergoes localized, rapid & severe
corrosion.
4.Purity of the metal: Presence of impurities in metal accelerate its corrosion. Eg.
Impurity of Pb or Fe or C is present in Zn, tiny electrochemical cells are set up, & Zn
corroded.
5. Physical state of the metal : Grain size-The rate of corrosion increases with a
decreases in grain size.
orientation-Corrosion rate of copper is not uniform at all the faces .
Stress- Area under stress is more anodic and undergo corrosion.
6.Nature of oxide film : In case of Aluminium oxide, lead oxide, tin oxide, volume of the
oxide is greater than the volume of metal consumed. On the other hand Alkali & Alkailne
earth metal Li, Na,K, Mg, Ca, Sn the volume of oxide is less than the volume of the
metal.
7.Solubility of the corrosion products: If Corrosion product soluble -corrosion rate
increases. On the other hand, if corrosion product is insoluble eg. PbSO4 in case of Pb in medium
of H2SO4, it forms a protective layer on the metal surface and inhibits further corrosion.
(B)Nature of the corroding environment:
1Temperature: Rate of corrosion increases with rise in temp eg. Intergranular corrosion
such as caustic embrittlement take place at high rate.
2.Presence of moisture: Presence of moisture accelerates the rate of corrosion. eg.
Rusting of iron increases rapidly when humidity of air is 60-80% in comparison to dry air.
3.Presence of corrosive gases in the atmosphere: The rate of corrosion increases in the
presence of CO2, H2S, fumes of HCl, H2SO4 gases due to acidity of the liquid .
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4.Nature of the ions present : Presence of chloride ion in the medium destroy the
passive film and increases the rate of corrosion. on the other hand presence of silicate
ions inhibit corrosion as they form an insoluble reaction product(silica gel).
5. Presence of suspended particles in the atmosphere: chemically active suspended
particles like NaCl, (NH4)2 SO4 form strong electrolytes, increases the rate of
corrosion.whereas chemically inactive suspended particles such as charcoal absorbs H2S,
SO2&moisture slowly increases the rate of reaction.
6.Condutance of the corroding medium: The flow of corrosion current depends on the
conductance of medium.For eg. Conductance of clay and mineralized soils is much
higher than those of dry sandy soils, that’s why metal structure buried under clay and
mineralized soils are damaged to larger extent.
7.pH of the medium:
Media
Acidic
Alkaline
Alkaline
pH
pH < 7
pH > 7
pH= 7
corrosion
more
Less than acidic
Less than acidic
8.Concentration of oxygen and formation of oxygen conc. cells:
Differential aeration sets up conc. cells which enhance the rate of reaction.
Protection from the corrosion(Preventive measures for corrosion control:
Material selection:
1.The chosen metal should be as pure as possible.
2.The corrosion resistance and strength of many metals can be increased by alloying
stainless steel is more resistant
3.Two metals should be choosen in such a way that their electrode potential are close as
possible.
4.Contact of the two dissimilar metals in the presence of corroding environment should
be avoided.
5.If an active metal is used , it should insulated from more cathodic metals.
Proper designing:
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i Localized stresses should be avoided: the design should avoid sharp bends, baffles,
lap joints, crevices.
ii, Accumulation of dirt and stagnation of water should be avoided: by
avoiding sharp corners and recess.
iii, Arrangement for the free circulation of air: allow free circulation, prevent the
formation of damp areas and stagnant pool.
Barrier protection:
protection of iron from rusting.
Methods: i. By coating the metal surface with paints: Thin coating of paints, enamels,
lacquers used eg. Iron sheets in bicycles, car, buses
ii By coating the metal surface with oils or greese: eg. Iron tools and machinery parts.
iii By coating the metal surface with non-corroding metals - non corroding metals Cr
eg. iron protected from rusted by coating with Ni or Cr through electroplating technique.
iv By coating the metal with certain chemicals: like FePO4- give tough adherent
insoluble film.
Sacrificial protection: Protection of metal by some other more active metal coated
on its surface. Metal to be protected is covered with a layer of more active metal.
Galvanisation of iron: protection of iron
Zn being more reactive (electropositive) than iron is used for covering iron surfaces.
“ The process of deposition of thin layer of Zn on iron surfaces is called Galvanisation
of iron
i.
ii.
By dipping- iron sheets dipped in molten Zn& then passed through hot rollers a thin uniform layer is obtained.
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Zinc dust
heated
vapour of zinc
condense
Zinc(thin uniform layer)
On sheet of iron
The thin layer of Zn present on the surface of iron prevents it to come in contact with the
atmospheric oxygen and moisture. Iron does not rust even when Zn coating develops scratches
or cracks, because Standard reduction potential of Zn is less than that of iron.
E0 Zn2+/Zn= -0.76 V
E0 Fe2+/Fe = -0.44 V,
In case of cracks, Zn-anode(oxi), Fe-cathode(red), Due to oxidation Zn layer form ZnCO3.Zn(OH)
Protection of iron by tin: Iron can be protected by deposition a thin layer of tin on it. The
process is called tinning. Tinning can protect iron as long as the coating is intact. If the coating
develops scratches or cracks, iron is not protected any more.( protective action of tin is different
from that of Zn which protect iron even when the coating develop cracks.
This is because the standard reduction potential of iron is less than that of tin.
E0 Fe2+/Fe = -0.44 V,
E0 Sn2+/Sn= -0.14 V
Due to this iron possesses a greater tendency to get oxidized as compared to tin.
If tin coating develops scratches or cracks, iron- anode(oxi), tin-cathode( red) , iron get rusted.
Protection of Copper by tin: Tin can protect copper as Zinc protect iron. Due to standard
reduction potential of tin is less than that of copper,.
E0 Sn2+/ Sn= -0.14 V,
E0 cu2+/cu= +0.34 V
Tin has greater tendency to get oxidized as compared to copper, if tin layer develops crack, tin –
oxidation and copper protected.
Cathodic protection (Electrical protection): For the structures immersed in soils,
Metal to be protected- cathode
1.Sacrificial anode protection (galvanic protection):
More reactive(electropositive) metal - sacrificial anode
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Used for the protection of underground pipes and tanks, underground cables, marine
structure
Reactive metal Zn/ Mg buried inside the pipe &connected by a wire.Mg- anode(oxi), Fecatho de(red)- e-s reduce O2 to OH-.
Mg →Mg2+ +2e- ,
O2 + 2H2O +4e- → OH-
2.Impressed current cathodic protection:
Metal structure (protected)- cathode(by applying an impressed current form D.C source in
opposite direction
Impressed current reverse the direction of corrosion current, so metal act as cathode
instead of anode
D.C source
Metal structure
-ve terminal
eg.Battery rectifier
+ve terminal
inert anode eg. Graphite,high
silica iron, platinised tiatanium
Anode buried in backfill composed of gypsum, bentonite, Na2SO4.
Anodic protection:
Applicable to those metal which exhibit passive behavior
Used to protect Fe, Al, Ti, Cr
The metal to be protected is passivated by applying a current in direction to be
more anodic. The externally applied current deposits a protective film on the
surface of metal& metal get passivated.
Device is called Potentiostate- 3 terminal connected to it
Terminal 1- tank, Terminal 2 – platinum auxiliary electrode, Terminal 3- reference
electrode.
Soil Corrosion: water mains, electric cables and other underground structure embedded
in the soil
Factors:
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I, Moisture and Electrolyte contents: The conductivity of non acidic soil depends on
moisture and electrolyte content of the soil. A cable passes under a paving has less
oxygen than the one lying under unpaved soil, the portion under the paving –anodic and
suffers corrosion.
ii Acidity of the soil: In highly acidic soil, metal undergo corrosion accompanied by the
liberation of hydrogen.
iii.Physical properties of the soil: Buried pipelines and cables passing from soil to
another suffer corrosion due to differential aeration . e.g. Lead pipeline passing through
clay & then sand are corroded because area under clay are less aerated as compared to
that covered under sand.
iv.Organic matter content of the soil: large organic matter- formation of soluble metal
complexes, accelerate corrosion process.
v.Presence of micro-organism in the soil: In waterlogged soil, the amount of free
oxygen is less, generate anaerobic bacteria causes microbiological corrosion.
Microbiological corrosion: “Deterioration of materials caused directly or indirectly by
microbes such as bacteria, algae, moulds/fungi”
The microorganism can develop in an environment with or without oxygen and are
classed as aerobic and anaerobic.
Examples
1. Sulphate reducing bacteria( Desulfovibrio desulfuricans): are responsible for
anaerobic corrosion of iron and steel- require sulphates, pH- 5 to 9, temp- 25 to
300C. corrosion product are black FeS and Fe(OH)2 are incapable of protecting
iron from further corrosion. The corrosion is intense and localized.
8H2O = 8H+ + 8OH-
Anodic solution of iron:
4Fe + 8H+ = 4Fe2+ + 8H
Depolarization, due to activity of bacterias: H2SO4 + 8H = H2S + 4H2O
Corrosion products:
Fe2+ + H2S = FeS + 2H+
3Fe2+ + 6OH- = 3Fe(OH)2
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2. Sulphur Bacteria( Thiobacillus): aerobic, oxidize sulphur to yield H2SO4 which
attack the iron, pH- 0 to 1
3. Iron and manganese microorganism: aerobic, forming insoluble hydrates of iron
and manganese dioxide, pH- 4 to 10, temp- 5 to 400C
4. Film forming microorganism(bacteria, fungi:,algae,diatoms):
Form microbiological film on iron surface leading to formation of local biological
concentration cells and cause corrosion.
6.LUBRICANTS AND LUBRICATION
Friction: When two surface are come close to each other during motion, a resisting force comes
into existence which tend to retard their motion. The resisting force is known as frictional force
and phenomena is termed a s friction.
Wear: The progressive loss of the substance from the surface of body by a mechanical action
is termed as wear.
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Lubricants and Lubrication: “any substance when interposed between two relatively sliding or
moving surface reduces the friction and wear between them called lubricants.
“The process of decreasing the frictional forces between the surface is called lubrication
(a) Solid Lubrication: The surface in contact are coated with a solid substance such as graphite.
(b) Fluid lubrication: A fluid is maintained between the two rubbing surface such as
hydrocarbon oil.
Functions of lubricants:
(i)
To reduce friction.
(ii) To reduce wear tear and surface deformations.
(iii) As coolant
(iv) Protects from dirt
(v) Act as seal (e.g. internal combustion engine)
(vi) Prevent corrosion
(vii) Transmits fluid power ( e.g. Hydraulic lift)
(viii) Improves efficiency of machine.
Mechanism of Lubrication:
(a) Fluid film lubrication/thick film lubrication or hydrodynamic lubrication
Lubricant film thickness 1000 Å
Speed is high
Load is light
Friction in systems with hydrodynamic or fluid film lubrication depends on:
• Thickness & viscosity of the lubricant(viscosity is not high)
• Relative velocity and area of contact between sliding surface
( )
=
•
•
Coefficient of friction is 0.001 to 0.003 in comparison to unlubricated system.
This type of Lubrication is generally employed in machine like sewing machine, watches,
clocks etc.
Example: Hydrocarbon oils blended with long chain polymers.
(b) Boundry/Thin film lubrication:
Lubricant film thickness is less than 1000 Å
The viscosity of oil is very low
Heavy load
Speed is very slow
Coefficient of friction is low 0.05 to 0.15
Thin layer of oil adsorbed by chemical/physical forces ( oiliness)
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The lubricants molecules should have
• Long chain hydrocarbon
• Polar groups to promote
• Good oiliness
• Low pour point
• Resistance to heat and oxidation
Example: Mineral oil, vegetable & animal oil(liquid lubricant), graphite/Molybdenum
disulphide(solid lubricant)
(c) Extreme pressure lubrication :
When moving surface are working under high temp & high pressure
Special additives(extreme pressure additives) are used
Lubricant film can withstand very high load and high temp due to their high M.P
Load is heavy
Speed is high
Used in wire drawing, machining of tough metals
Durable film thickness (100-10000A)
Examples: chlorinated esters, sulphurized oils, tricresyl phosphates
Classifiaction of Lubricants:
(a) Solid lubricants:
are used when operating temp is too high & oil does n’t stay
contamination of lubrication oil is noticed
Example: Graphite and molybdenum disulphide
(1) Graphite:
Structure: sp2 hybridization, each C attached to three C atom, planar hexagonal ring
constitute huge sheets/ layer. C-C bond length= 1.42 0A, sheet distance( by vander Waals
forces)= 3.40A
Graphite is soft due to weak vander Waals forces.
Properties: soapy to touch, noniflammable, not oxidized in air below 3750C, low
coefficient of friction
Uses: 1.in powdered form/ as suspension in oil/water with tannin 2. Oil dag( graphite in
oil) in internal combustion engine 3. Aqua dag( graphite in water) 4. Graphite greases in
high temp application.
(2) molybdenum disulphide:
Structure: like sandwich , Mo layer lie in b/w two layer of sulphur, S-S bond
length= 6.260A
Properties: low coefficient of friction, stable in air upto 4000C, slightly softer
Uses: in shaft bearing of jaw crushers, machine tool gearing, coal conveyer belt
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(b) Semi solid lubricants (Greases):
Obtained by combining lubricating oil(can be petroleum gel/synthetic hydrocarbon) with
thickening agents( soaps of Na, Al, Ca, Ba) known as grease.
Machine is required to work under high load and low speed
Uses: in rail axle boxes, tractor rollers, in machine preparing textiles, edible articles
Classification of greases on the basis of the soaps ;
1.Lime/calcium based greases- prepared by saponifying fatty oil+ Ca(OH)2, water resistant, do
not possess good high temp properties,eg. Water pumps, tractors
2. Soda base grease - Prepared by saponifying a fat(tallow/ fatty acid)+ NaOH+ lubricating oil,
possess good high temp properties , used upto 1750C, eg. Ball bearing
3. Lithium based grease – prepared by petroleum oil+ Li soap, water resistant, use at high temp
eg. in aircraft
4. Resin soap/axle grease- prepared by lime/ heavy metal hydroxide+ Resin + fatty oil+
fillers(talc/mica), water resistant, eg. rail axle boxes, machine bearing, tractors rollers, wires
ropes
(c)Liquid lubricant: lubricating oils are also known as Liquid lubricant
Characteristics : high B.P, low F.P, high resistant to oxidation & heat, non corrosive
properties
Functions: as cooling & sealing agent
1. Animal and Vegetable oil: obtained from animal & vegetable
Oiliness- property which is responsible for sticking of oil to machinery parts.
eg(Vegetable oil): olive,castor,palm, cotton seed oil
eg( Animal oil): Lard, tallow,whale, seal oil
2. Mineral oil: known as petroleum oil, obtained by fractional distillation of crude petroleum at
atm pressure., quite stable, available in abundance, poor oiliness as compared to animal and
vegetable oil
3. Blended/Compounded oil: properties of petroleum oil improved by adding specific
additives. The oil obtained are called Blended oil
Eg.
Additives for lubricants: Compound which improve the desired qualities of lubricants are
termed as additive
1. Oiliness improvers: increase the oiliness of lubricant and strength of oil film .eg. fatty acid,
fatty amine, vegetable oils.
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2. Viscosity index improvers: reduce the rate of change of viscosity with temp. eg.
Polyisobutylene, polystyrene, alkyl acrylate/polyesters
3. Antioxidants: increase the resistance of oil toward oxidation. eg. Phenols, amines, organic
sulphides and phosphides.
4. Rust and corrosion inhibitors: used to protect bearing and other meal surface from
corrosion. eg. Fatty acid and amines, metal sulphonates, metal phenolates, alkyl succinic
acid
5. Antiwear additives: reduce rapid wear in steel-on steel applications . eg. Zinc
dithiophosphates, organic phosphates and acid phosphates.
6. Extreme pressure additives: adsorbed on metal surface, preventing the tearing up the
metal.eg. fatty ester, acid, organic chlorine compound, organic phosphorous compound.
7. Pour point depressants: prevent the separation of wax from oil eg. Phenol,
polymethacrylate, chlorinated wax with naphthalene.
8. Antifoam additives: prevent the formation of stable foam eg. Silicon polymers, glycols,
glycerols.
9. Emulsifiers: promote the mixing of mineral oil with water. eg. Sodium salt of carboxylic
and sulphonic acid
10. Detergents & deflocculants: clear machine parts from dirt & dust eg. Calcium and barium
salt of sulphonates and phosphonates.
11. Dispersants: reduce or prevent sludge formation under low temp. eg. Alkyl succinimides
and polymeric alkyl-thiophosphonates.
Properties of lubricants:
(a)Viscosity –
The coefficient of viscosity defined as the tangential force required per unit area to maintain
unit velocity gradient between two parallel planes in the fluid unit distance apart. In C.G.S and
S.I system , the unit of viscosity is poise and pascal sec respectively.
Determination of viscosity –Redwood viscometer 1 and 2
Redwood viscometer 1 - used for thin lubricating oil, jet bore diameter 1.62 mm& length 10
mm
Redwood viscometer 2 – used for thick lubricating oil, jet bore diameter -3.8 mm and length 50
mm .
Viscosity index: The variation in the viscosity of a lubricating oil with temp is called viscosity
index. High viscosity index- viscosity change a very low rate.
Low viscosity index- viscosity change rapid rate.
Determination of viscosity index–
V.I = L - U/ L – H x 100
U= viscosity of oil at 1000F under test,
L= viscosity of Gulf oil at 1000F which has the same viscosity of oil under examination at 2100C
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H= viscosity of Pennsylvanian oil at 1000F which has the same viscosity of oil under
examination at 2100C
(b)Flash and fire point :
Flash point of an oil is the minimum temp at which it gives sufficient vapour that ignite for a
moment , when a flame of brought near the surface of oil.
Fire point of an oil is the minimum temp at which it gives sufficient vapour that burn
continuously for at least five second , when a flame of brought near the surface of oil.
Determination of Flash and fire point: Penskey -Marten’s apparatus
(c) Cloud point and pour point: “ when a lubricating oil is cooled in a standard apparatus at a
specific rate, the temp at which the oil becomes cloudy or hazy in appearance is called cloud
point and the temp at which the oil ceases to flow or pour is called pour point”
A good lubricating oil should possess low pour point.
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(D)Aniline point : “ Minimum temp at which the equilibrium exists between equal volumes of
aniline and oil.
(E) Neutralization Number/ acid value: It is the no. of milligram of KOH required to neutralized
the free acid in 1 gram of the oil. Acid value should > 0.1 for lubricating oil,
Acid value < 0.1 oil is oxidized.
V o lu m e o f K O H u s e d ( m l) x N o rm a lity x E q . w t o f K O H
A c id v a lu e
W e ig h t o f s a m p le
(F)Saponification number: It is the milligram of KOH required to saponify fatty material present in one
gram of oil.
Volume of KOH used(ml) x Normality x Eq. wt of KOH
Saponification value
W eight of sample
(G)Iodine value/ iodine number : number of grams of iodine equivalent to amount of iodine
monochloride(ICl) consumed by 100 g of the oil.
Iodine value
Volume of hypo (ml) x Normality of hypo soln x Eq. wt of I 2
W eight of sample
BIODERADABLE LUBRICANTS: Type of lubricants which are easily decomposed or destroyed
when spilled on to open land or into water, without leaving behind harmful substances. eg.
Plant based oil or lubricant like sunflower oil, mustard oil, soyabean oil
Advantages:
I, easily available ii reduces the environmental pollution iii reduces the energy consumption
iv. low cost v. high viscosity index vi high flash/fire point eg. Soyabean oil is 3260F higher than
of flash point of mineral oil 3920F vii Plant based biodegradable lubricants are less toxic.
Disadvantages: I Vegetable oil have low oxidative stability-oil will oxidize quickly
Ii Vegetable oil have very high pour point .
Importance: in industries, reduces environmental pollution and energy consumption.
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7. Polymers
Monomers: Large molecule of very high molecular mass formed by the repeated combination of large
number of one or more types of small molecule called monomers
Polymerization: is a chemical combination of a number of similar or different molecules to form a single
large molecule. For eg. Polyethylene is a chemical combination of large number of ethylene molecule.
n CH2=CH2
-(CH2-CH2-)-n
Repeating unit: The structural unit which on repetition gives the entire chain of a polymer
molecule is called repeat unit.
Monomer
Repeating unit
n CH2=CH2
- CH2-CH2--
n CH2=CH-CH=CH2
n CH2=CH-CN
- CH2-CH=CH-CH2-
- CH2-CH
CN
Functionality: The number of bonding sites present in a monomer is referred to as its functionality.
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Bonding sites
H2C- CH2
H2C=CH2
Bonding site-2
-- Bifunctional
Bonding site-3
-- Trifunctional
Bonding site- >3 -- Polyfunctional
Degree of polymerization: The number of repeating unit present in a molecule present in a polymer is
referred to as degree of polymerization.
Oligopolymers: low degree of polymerization
High polymers: High degree of polymerization
Homopolymers: The polymer obtained by repeated combination of only one type of monomer
molecule called homopolymer. eg. Polyehylene is a homopolymer of ethylene .
Copolymers: The polymer obtained by repeated combination of two or more type of monomer
molecule called copolymer. eg. Nylon-66 is a copolymer of hexamethylenediamine and adipic acid .
Classification of Polymers
1 On the basis of source of origin
(a) Natural polymer : eg. Starch, cellulose, proteins, Nucleic acid, rubber
(b) Synthetic polymer: eg. Polyethylene, polystyrene, polyvinyl chloride, nylon, teflon, synthetic
rubber
2 On the basis of synthesis :
(a) Addition polymerization: large no. of monomer molecule add up together to form polymer
chain without elimination of small molecule like H2O, NH3, alcohol eg. Polyethylene,
polypropylene.
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n CH2=CH2
-(CH2-CH2-)-n
Ethylene
Polyethylene
(b) Condensation polymerization: occurs between monomers containing two or more functional
groups with loss of small molecule like H2O, NH3, alcohol. So repeating unit is not the same as
monomer. eg. Nylon -66
H
nH2N-(CH2)6-NH2
Hexamethylenediamine
+ nHOOC-(CH2)4-COOH
HO
O
-N--(CH2)6-N-C-(CH2)4-C-)n + 2nH2O
Adipic acid
Nylon 66
3 On the basis of structure:
(a) Linear polymer :
Polymeric chain stack one another
High densities, high tensile strength, high M.P
Eg. High density polyethylene
(b) Branched chain polymer :
Side chain attached to main chain
Don’t have packed structure
Low densities, low tensile strength, low M.P
Eg. Low density polyethylene
(c) Cross linked polymer:
Adjacent polymeric chain link together through side chain
Three dimensional structure
Hard, brittle, rigid
Eg. Phenol formaldehyde, urea formaldehyde
4
On the basis of molecular forces:
(a) Elastomers:
Weakest intermolecular force
Stretched due to intermolecular force
Cross liks introduced when force applied
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Eg. Synthetic rubber, and natural rubber
(b) Fibres:
Strong intermolecular force-hydrogen bonding & dipole-dipole interaction
High M.P, high tensile strength, high modulus
Close packing of polymeric chains
Eg, Nylon 66(hydrogen bonding), Polyesters, polyacrylonitriles(strong dipole-dipole
interactions)
(c) Thermoplastic :
Intermolecular forces are intermediary
Formed by addition polymerization
Linear polymers, no cross link
At room temp-hard, on heating- soft, easy moulded, on cooling-hard
Eg. Polyethylene, Polypropylene, polystyrene, teflon
Plasticizers: workability of thermoplastic at low temp increased by adding organic
compound ,it help to soften at low temp
Eg. Dialkyl phthalates, cresyl phosphates,
(d) Thermosetting:
On heating change irreversibly into hard, rigid, infusible material
Formed by condensation
Croos link, three dimensional network
Rigid, does not soften on heating, can not reprocessed.
Eg. Phenol formaldehyde, Melamine formaldehyde, urea formaldehyde
Mechanism of polymerization:
1. Free radical addition poymerization
2. Ionic polymerization- (a) cationic (b) anionic
3. Coordination polymerization
1. Free radical addition polymerization: formed by the successive addition of monomer
units to growing chain having a reactive intermediate (called chain growth polymers)
3 steps:
(a) Initiation: requires a initiator produces reactive intermediate such as free radical
Heat
R-CO-O-O-OC.R
organic peroxide
.
R-CO-O
.
2R + 2CO2
Free redical
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.
2R
+
Free redical
.
H2C=CH2
R-CH2-CH2
Monomer with active centre
Ethylene
Intermediate
(b) Chain propagation:
.
R-CH2-CH2
.
H2C=CH2
H2C=CH2
R-CH2-CH2-CH2-CH2
Dimer with active centre
.
R-(CH2-CH2)2-CH2-CH2
Trimer with active centre
.
R-(CH2-CH2)x-CH2-CH2
Polymer with active centre
(c) Chain termination:
. .
R-(CH2-CH2)x-CH2-CH2 + CH2-CH2-(CH2-CH2)y-CH2-R
R-(CH2-CH2)n-R
Another growing polmer chain with growing polymer
Polymer without active centre
2. Ionic addition polymerization: Formation of carbonium/ carbocation ion
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(a)Cationic addition polymerization: chain carriers are positively charged carbonium
ion. eg Polymerization of isobutylene using BF3 as catalyst and water as cocatalyst. It
involves initiation, propagation, termination step.
(b)Anionic addition polymerization: chain carriers are negatively charged carbanions
ion. eg Polymerization of styrene using alkali metal alkyls, Grignard reagent. It
involves initiation, propagation, termination step.
3. Coordination polymerization: Polymerization reaction take place in the presence of
organometallic compound as catalyst are termed as coordination polymerization.
Ziegler-Natta catalyst (combination of transition metal halide TiCl4/ TiCl3 with
organometallic compound) is used to catalyzes the reaction. eg. Polymerization of
propene in presence of Ziegler-Natta catalyst. it also involves initiation, propagation,
termination step.
Effect of structure on properties of polymers:
1. Molecular mass and degree of polymerization: Molecular mass depends upon the number
of monomer units present in a molecule referred to as degree of polymerization.
Low molecular mass- soft &gummy, high molecular mass-tougher and heat
resistant
2.Shape of molecule:
Linear polymer :
Polymeric chain stack one another
High densities, high tensile strength, high M.P
Eg. High density polyethylene
Branched chain polymer :
Side chain attached to main chain
Don’t have packed structure
Low densities, low tensile strength, low M.P
Eg. Low density polyethylene
Cross linked polymer:
Adjacent polymeric chain link together through side chain
Three dimensional structure
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Hard, brittle, rigid
Eg. Phenol formaldehyde, urea formaldehyde
3.Intermolecular force of attraction:
Strong Intermolecular force of attraction-high M.P, high tensile strength eg. Polyesters
Weak Intermolecular force of attraction-have stretching properties eg. Elastomers.
Plastic deformation: Thermoplastic subjected to heat, it get deformed known as plastic
deformation: linear polymers easily deformed but cross linked do not undergo plastic
deformation.
4.Crystallinity and amorphousness:
constituent macromolecules
(i)in random arrangement—amorphous state,
(ii)in definite crystalline arrangement-- crystalline state.
Eg. Polyethylene(chains are regular in zig-zag motion)-highly crystalline, Polystyrene(contain
bulky gp)-amorphous in nature.
5.Nature of monomer unit: Cellulose polymer contain free OH gp
Cellulose acetate making thin films, nitrocellulose used as explosive
Natural rubber have double bond react with ozone.
6.Geometric arrangement of double bonds in polymeric chain:
Natural rubber - cis isomer Gutta parcha- trans isomer.
Biodegradable polymerization: polymers which are degraded by microorganism within a
suitable period so that biodegradable polymers and their degraded products do not cause any
serious effect on environment.
Most imp class of biodegradable polymers are aliphatic polyesters and polyamides.
EXAMPLES:
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1. Polyhydroxy Butyrate(PHB)- is obtained from 3-hydroxybutanoic acid
O
HO-CH-CH2-C-OH
Condensation
O
{O-CH-CH2-C }n
CH3
CH3
polyhydoxybutyrate
3-hydroxybutanoic acid
2. Poly-β-hydroxy Butyrate-co- β hydroxyl valerate (PHBV)- copolymer of 3hydroxybutanoic acid + 3-hydroxypentanoic acid in which the two monomer units are
connected by ester linkages.
O
O
nHO-CH-CH2-C-OH
nHO-CH-CH2-C-OH
+
CH2CH3
CH3
3-hydroxypentanoic acid
3-hydroxybutanoic acid
Polymerization
-[-O-CH-CH2-C-O-CH-CH2-C-]-n + (2n-1)H O
2
CH3
O CH2CH3 O
PHBV
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The properties of PHBV according to ratio of both the acid where as 3-hydroxybutanoic acid
provides stiffness and 3-hydroxypentanoic acid imparts flexibility.
Uses: 1. Packaging 2. Thopaedic devices and in controlled drug release. When a drug is enclosed
in a capsule of PHBV, it released only when the polymer is degraded in the body.
3. Polyglycolic caid(PGA)- is obtained by the chain polymerization of cyclic dimer of
glycolic acid.
O
O
nHO-CH2-C-OH
condensation
-(-O-CH2-C--)n-
Glycolic acid
Polyglycolic acid
Uses: 1. As sutures ie. For stitching of woundfs after operation. The polymer get degraded
within the body in about week time. During this degradation, the polymer undergo hydrolysis
to form small nontoxic molecules which are excreted without causing any harm to body.
4. Polylactic acid(PLA)- obtained by polymerization of cyclic dimer of lactic acid or by
microbiological synthesis of lactic acid followed by polycondensation and removal of water by
evaporation.
O
HO-CH-C-OH
O
condensation
-(-O-CH-C-O-)n-
CH3
CH3
Lactic acid
Polylactic acid
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A polymer of PGA and PLA (90:10 ) is used to make absorbable sutures to close an internal or
external wound and has replaced catgut. These are completely degraded and absorbed by the
body within 15 days to one month of surgery.
5.Nylon-2-Nylon 6 – It is an alternating polyamide glycine (containing 2 carbon atom and and 6aminocaproic acid(containing 6 carbon atoms).
NH2-CH2-COOH + H2N-(CH2)5-COOH
- H2O
NH2-CH2-CO- NH-(CH2)5-COOH
Repeat
-(-NH-CH2-CO- NH-(CH2)5-CO-)-n
Biopolymerization: Polymerization process for the production of biopolymers is called
biopolymerization.
Type of biopolymerization:
1. Using microbes to produce bioplastic- Microbial biopolymers made by using microbes.
These are polyesters that are produced by a range of microorganisms cultivated under various
nutrient and growth condition. Bioplastic made from compound called Polyhydroxy-alkanoate
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Bacteria accumulate PHA in the presence of excess carbon source, similar to accumulation of
fat deposit on bodies of human after the consumption of excess food.
eg. Poly 3-hydroxy-butyric acid(PHB)
2.Using fermentation – Fermentation is the use of microorganism to break down organic
substances usually in the absence of oxygen. Bioploymers and bioplastics can be made by the
following two type of fermentation processes.
(a) Bacterial polyester fermentation-Ralstonia eutropha bacteria( a microorganism) use the
sugar harvested plant(such as corn) to fuel their cellular processes. The by product of this
cellular process is poluester which is then separated from the bacterial cell.
(b) Lactic acid fermentation- Lactic acid is fermented from sugar causing bacteria. After the
lactic acid is produced by fermentation process, it is converted to polylactic acid.
3. Growing plastics in plants: A genetically engineered plant Arabidopis thaliana contains the
enzyme used by bacteria. Bacteria create the plastic through the conversion of sunlight into
energy. The scientist have transferred the gene that codes for this enzyme into plant, as a
result, the plastic is produced through cellular processes of plant. The plant is harvested and
plastic is extracted from it using a solvent. Using distillation process, plastic is separated from
solvent.
Advantages of biopolymerization:
i.
ii.
iii.
Biopolymerization is ecofriendly synthesis process
The product biopolymer is degradable
Biopolymer is derived from renewable resources and possesses good mechanical
properties.
Some imp polymers:
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Thermoplastic
1.Polyvinyl chloride :
Preparation: Free radical addition polymerization of vinyl chloride in presence of benzoyl
peroxide.
Properties: 1. colourless, odourless, non inflammable 2. Softening point- 1400C 3. Resistance to
atmospheric oxygen
Uses: in making sheets for making tank lining, refrigerator part, helmet, light fitting
2.Polyvinyl acetate:
Preparation: Free radical addition polymerization of vinyl acetate in presence of benzoyl
peroxide.
Properties: 1. colourless, soft and sticky material 2. Soluble in organic solvents 3. Resistance to
atmospheric oxygen , water mineral acid, alkalies.
Uses: making chewing gums, surgical dressing, for coating on wrapping paper
3.Teflon(Polytetraflouro ethylene):
Preparation: Free radical addition polymerization of tetraflouroethylene under pressure which
act as free radical initiator.
Properties: 1. Highly crystalline linear polymer 2. high M.P-3270C 3. Softenning point is high 4.
Good electrical insulator
Uses: Making valves and lining of parts, used in making non sticking kitchen utensils and in
electric irons.
Thermosetting:
1.Phenol formaldehyde resin:
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Preparation: condensation polymerization of phenol and formaldehyde in presence of
acidic/alkaline catalyst
Properties: 1. Hard, rigid, infusible solid mass 2. insoluble in organic solvent 3. Possess
excellent electrical insulator character
Uses: in moulding application, in making telephone parts, TV, radio and automobile parts, in
the manufacture of varnishes, paints and protective coatings . It is widely used for making
switches plugs, switch boards.
Urea formaldehyde resin:
Preparation: condensation polymerization of Urea and formaldehyde in presence of
acidic/alkaline catalyst
Properties: 1. clear are hard materials 2. Good chemical resistance and good electrical
insulator. 3. Good adhesive characteristics
Uses: in manufacture of buttons, bottle caps, surgical items, cosmetic, container closures,
household appliances
Synthetic rubber:
1.Styrene butadiene rubber (SBR or Buna S or GR-S):
Preparation: polymerization of mixture of 75% butadiene and 25% styrene.
Styrene: obtained from benzene and ethylene.
Butadiene: Catalytic dehydrogenation of butane or butane at 400-6600C.
Properties: 1. It swells in organic solvent 2. High load bearing capacity, high abrasion
resistance and low oxidation resistance
Uses: in manufacture of motor tyres, shoes soles, gaskets, floor tiles, cable insulation adhesive,
carpet backing.
2.Nitrile rubber (Buna-N, GR-N/ NBR):
Preparation: polymerization of butadiene and acrylonitrile.
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Properties: 1. It swells in organic solvent 2. Possesses extraordinary resistance to oils. Acids,
salts, abrasion, heat & sunlight.
Uses: 1. Used for making fuel tanks, conveyor belts, automobile parts, high altitude air craft
component.
Sillicones: synthetic organosillicon polymers containing repeated R2SiO units held together
by Si-O-Si linkages.
Genaral formula: (R2SiO)n, R-alkyl/aryl gp,
Silicon polymers linear, crosslinked or cyclic.
Preparation: Linear silicones are obtained by hydrolysis of dialkyldichlorosilane or
diaryldichlorosilane(R2SiCl2 yields a silanediol which undergoes condensation polymerization to
form linear silicone.
Cross linked silicones: prepared by the hydrolysis of alkyl trichlorosilanes, RSiCl3
Properties 1. Short chain (lower silicones) - oily liquid
Medium chains
- viscous oil
Long chain(higher silicones) - rubbery
2.Water repellent and heat resistant. 3. Stable upto 2000C and nonvolatile on heating.,
3. Chemically inert 4. Act as electrical insulator.
Uses: used to form water resistant coatings on glass, clothes, paper, wood and wool. Sillicones
rubbers are used as insulating material.
Polymer composites: Polymer may be mixed with some other polymer or nonpolymeric
material to incorporate additional properties. The resultant mix becomes more useful as
compared to the original polymer is called polymer composite.
Three categories
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1.Fibre reinforced plastic- prepared by bonding fibre material+ resin matrix under heat and
pressure.Bonding fibre material may be glass/alumina/graphite/aromatic polyamines. Resin
matrix may be polyesters/phenolic resins/silicon resin/ melamine resins.
Properties: Strength of Glass reinforced plastic (GRP) increases with increase fibre length.
Increase in glass content in GRP increases its tensile and impact strength.
2Polymer blends: Simple physical combination of two or more incompatible polymer is called
polymer blend.
Properties: 1. Blending improves the properties like workability resistance to abrasion and
impact strength. 2. Helpful in protecting a polymer from degradation .
Examples: Nylon-6 polycarbonate blend, ABS plastics, Polydimethylphenylene-poystyrene
blend.
3.Polymer alloys: “Compatible mixture of two or more polymers which interact chemically
under specific sets of conditions of compostion, temp and pressure.”
Example: ABS-PC alloys
SECTION D
8.INSTRUMENTAL METHOD OF ANALYSIS
Thermogravimetric analysis(TGA): “Measurement of change in mass of a system with increase
in temp at a linear rate” .
Thermogram- a plot of mass vs temp
Differential thermogram- a plot of dm/dt vs temp
Type of thermogravimetric analysis:
1.Dynamic thermogravimetric analysis- temp is increased continuously linearly with time.
2. Static(isothermal) thermogravimetric analysis- temp is maintained constant over a definite
period of time and change in mass is noted.
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Principle and techniques: Themogram or TGA curve is characteristic for a given compound
because of the physicochemical changes take place during the heating of a compound over
definite temperature ranges are related to its molecular structure.
A thermogram consists of horizontal portion called plateaus (stable phase over the temp
interval, curved portion-inflexions (unstable phase over the temp interval due to formation of
an intermediate compd.
Eg. Thermogram of CaC2O4.H2O
CaC2O4.H2O
-H2O
CaC2O4
-CO
CaCO3
-CO2
CaO
Fig: Thermogram of CaC2O4.H2O
Temp
Thermal event
change in mass
18-1000C
1st plateau -CaC2O4.H2O is thermally stable
100-2260C
1st inflexion-CaC2O4.H2O→CaC2O4 (anhydrous) + H2O
226-3460C
2ndplateau -CaC2O4 is thermally stable
No change in mass
346-4200C
2nd inflexion-CaC2O4. →CaCO3 (anhydrous) + CO
decrease in mass
420-6600C
3rd plateau –CaCO3 is thermally stable
No change in mass
No change in mass
decrease in mass
660-8400C
3rd inflexion-CaCO3. →CaO (anhydrous) + CO
decrease in mass
840-9800C
4th plateau – CaO is thermally stable
No change in mass
Applications:
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1.In testing the purity of a sample 2. In the study of organic compound 3. In the study of
polymers 4. In the study of building materials 5. Determination of chemical stability of both
primary and secondry standard
Differential thermal analysis (DTA): “ Measurement of a temp diff of a sample and thermally
inert reference material(alumina) as a function of sample/reference/furnace temp”.The thermal
effects may be due to endothermic or exothermic, caused by physical changes whereas
enthalpy effects caused by chemical reactions.
Principle and techniques: DTA involves the measurement of thermal/enthalpy effects
associated with the physical & chemical changes by a differential method in which the sample
temp is continuously compared with the temp of thermally inert reference. The diff in temp is
called differential temp (Δ T) which is recorded as a function of reference material temp/
furnace temp/time.
A peak above Δ T- exothermic change, peak below Δ T- endothermic change.
e.g Themogram of CaC2O4.H2O- two minima(endothermic) and one maxima( exothermic)
Peak area(A)= ∫t2 Δ T.dt = qa2/ 4λ where Δ T-differential temp, q-heat of transition per unit
volume, a- radius of sample chamber, λ- thermal conductivity of sample.
Applications: 1. In study of ceramics, mineralogy & metallurgy 2. In the study of phase
reactions and phase transformations 3. In the characterization of polymers and other organic
compound 4. In the study of cocordination & other inorganic compound. 5. In the
determination of M.P & B.P. 6. Determination of specific heat 7. In industries 8. In
determining thermal stability 9. In analytical chemistry 10. In physical chemistry
Differential scanning colorimetry (DSC): “involves the heating of a sample and reference
material in such a way that two remain at the same temp. The heat added either to sample or
to the reference material depending upon endothermic or exothermic changes during heating.
The added heat is recorded as a function of temp.
Heat supplied to the sample = +ve
1mcal/s.
Heat supplied to the reference = -ve , heat is order of
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Area enclosed by a peak in DSC thermogram is given by A =k’m ΔH,
of temp, m = mass of the sample, ΔH- heat of reaction.
k’- constant independent
Applications: 1. In determination of enthalpy of transitions 2. In determination of purity of
drugs 3. In the study of organic compounds.
Basic concept of spectroscopy:
Atomic spectra is due to electronic transition, but in molecular spectra vibrational &
rotational transition also takes place in addition to electronic transition.
Electronic excitation are caused by high energy radiations like UV radiations, whereas
vibrational/ rotational energy levels can be raised by low energy radiations like infrared
radiation.
Spectroscopy- is the branch of science which deals with transition occurring in a molecule
when it interact with the electromagnetic radiation. Eg. UV, IR, NMR, EPR, flame photometry,
Basic principle- Electromagnetic radiation provides energy equal to the energy difference ΔE
between the excited and ground state which is equal to
ΔE= h ν where h is Plank constant and ν = frequency of the radiation
Type of Spectroscopy1. Emission spectroscopy- “transition of an electron from a state of high energy to a state of
lower energy, energy is emitted as a photon, the spectra obtained is called emission spectra
and spectroscopy is called Emission spectroscopy. eg. Flame photometry.
2. Absorption spectroscopy- “transition of an electron from a state of low energy to a state of
high energy, energy is absorbed, the spectra obtained is called absorption spectra and
spectroscopy is called absorption spectroscopy.
Spectrophotometry- It is technique used to record the absorption spectra of liquids. It gives
spectra in which the light is absorbed or transmitted through a solution as a function of
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wavelength. The apparatus used in this technique is called spectrophotometer. It may be
manual or automatic. They may be single beam or double beam.
Laws of light absorption:
1, Lambert’s law: “ Rate of decrease of the intensity of incident radiation with respect to the
thickness of the medium is proportional to the intensity.”
-dI/dx= k.I, k is constant called absorption coefficient.
Є= 1/x Є - extinction coefficient defined as equal to reciprocal of the thickness of the
medium which reduces the intensity of light to one tenth of its original value.
2, Lambert-Beer law: “ Rate of decrease of the intensity of incident radiation with respect to
the thickness of the medium is proportional to the product of intensity and conc..”
-dI/dx= k.c.I, k is constant called absorption coefficient. Є’ = 1/x , Є’ - molar
extinction coefficient defined as equal to reciprocal of the thickness of the of 1M solution
which reduces the intensity of light to one tenth of its original value.
Type of molecular energies:
1. Transational energy: The kinetic energy possessed by molecule due to free motion in
space called transational energy.
2. Roatational energy: It is associated with the rotational motion of the molecule about
the centre of gravity is called roatational energy.
3. Vibrational energy: The energy associated with the vibration of the constituent atom in
the molecule called vibrational energy.
4. Electronic energy: Energy involved in the excitation of electrons into higher energy level
or due to changes in the distribution of electrons by cleavage of bonds is called electronic
energy.
Type of spectra depending upon the energy levelsEnergy required for the transition follow the order.
Electronic > vibrational > electronic
1. Rotational band spectra 2. Vibrational -rotational band spectra 3. Electronic band
spectra
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Interaction of radiation with a molecule and origin of the spectrum1. Radiofrequency region- nucleus and electrons – charged particles behaves as magnetic
dipoles due to spin and interact with the magnetic field .
2. Microwave region- The absorption of radiation take place when oscillating dipole
interacts with the electric field of radiation. The absorbing molecule behave as
oscillating dipole due to rotation.
3. Infra red region- The absorption of radiation take place when oscillating dipole
interacts with the electric field of radiation. The absorbing molecule behave as
oscillating dipole due to vibration.
4. Visible and UV region- Excitation of electrons from a lower to higher level produces a
change in electric dipole which interact with the electric field of radiation and give rise
to electromagnetic spectrum.
Vibrational (infrared ) spectroscopy: “ The branch of spectroscopy which deals the
interaction of molecule with electromagnetic radiation having wave number 667-4000
cm-1 called infrared spectroscopy’’. Infrared region lies in between visible and
microwave region of electromagnetic spectrum.
Far infrared
50 – 667 cm-1
Ordinary infrared 667-4000 cm-1
Near infrared - 12500 – 4000 cm-1
Finger print region- 900-1400 cm-1
Principle: When radiation frequency range less than 100 cm-1 are absorbed molecular
rotation takes place and discrete lines are formed.
When radiation with frequency 100-10000 cm-1 are passed through sample, molecular
vibration get set up.
Vibrational energy depends upon
i, Masses of atoms present in a molecule
ii, Strength of bonds
iii, the arrangement of atoms within molecule.
Homonuclear diatomic molecule are unable to absorb radiation because they possess zero
dipole moment called infrared inactive. Heterodinuclear diatomic or polyatomic molecules
possess permanent dipole moment called infrared active.
Type of molecular vibration:
Molecular vibrations are of two types
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1. Stretching
2. Bending
1.Stretching vibration: In stretching , the distance between the two atoms increases or
decreases but the atoms remain in the same bond axis.
Stretching vibrations require higher energy and occur at high frequency.
Stretching vibration are of two types 1. Symmetrical 2. Asymmetrical
i Symmetrical Stretching vibration: In this type of vibration , the movement of atoms with
respect to particular atom in a molecule in the same direction.
ii Asymmetrical Stretching vibration: In this type of vibration , the movement of atoms with
respect to particular atom in a molecule in the opposite direction. One atom approaches the
central atom while the other departs.
2.Bending vibration: in bending, the positions of the atom change with respect to the original
bond axis or atoms move in and out of the bond axis plane. These vibration involve a change in
bond angle. Bending vibration require lower energy.
They are of 4 types
i, Scissoring: In this type, the two atoms around the central atom tend to approaches each
other.
ii, Rocking: In this type, the movements of atoms takes place in the same direction.
iii, Wagging: In this type, the two atoms moves up and below the plane with respect to central
atom.
iv, Twisting: In this type, one of atoms move up the plane while the other moves down the
plane with respect to central atom.
Number of fundamental vibrations and fundamental frequency:
For infrared spectroscopy, the molecules should not be centrosymmetric , the molecules which
are not centrosymmetric called IR active. The IR spectrum of a molecule results due to
transition between two different vibrational energy levels. The vibrational energy of chemical
bond is quantized and can have the value
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E vib = (V +1/2) hν, V= 0,1,2,3 known as vibrational level, ν- vibrational frequency of the
bond.
Fundamental bands: Transition from the ground state (v = 0) to first excited state (v=1)
absorbs radiation strongly and give rise to intense bands called fundamental bands.
Overtones: transition from the ground state (v = 0) to second excited state (v=2) with the
absorption of infrared radiation give rise to weak bands called overtone.
Vibrational spectra of polyatomic molecules:
Fundamental frequency:
The frequency associated with the fundamental vibration of molecule is called fundamental
frequency. Every molecule is associated with a number of fundamental vibration. 3N-6 for
nonlinear, 3N-5 for linear molecule, N= no. atoms present in a molecule.
Linear molecule eg. i, linear triatomic molecule CO2 ii bent triatomic molecule H2O, NO2
Vibrational spectra of diatomic molecules:
For homonuclear diatomic molecule H2, Cl2,O2 because of zero dipole moment for all bond
length, no vibrational energy exchange would be possible, such molecules would be infrared
inactive.
For heteronuclear diatomic molecule linear HCl, CO, NO possess permanent dipole moment
hence infrared active.
Application of IR spectroscopy:
1. Identification of an organic compound 2. Detection of functional group 3. In detection of
impurities in a sample 4. Studying the progress of the reaction 5. Presence of hydrogen
bonding in a molecule 5. Presence of water in a sample
Electronic spectroscopy(UV-Visible): is concerned with the change in the electronic energy
level of the molecule.
1. Ultraviolet region:
Near ultraviolet region 200 - 400 nm
Far ultraviolet region 100 - 200 nm
2. Visible region :
400-1000 nm.
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Principle: When a substance is placed in UV/ visible region of electromagnetic radiation,
the electron get exicted from a lower energy to high energy level. Due to this the electronic
state of the molecule get changed. Each electronic energy level in a molecule is associated
with a number of vibrational sublevel with small energy difference. Each vibrational level is
associated with a small number of rotational sublevel.
Type of electron involved in the transition: There are 3 types of electrons
1. ∏ electrons: in double and triple bond in unsaturated compound.
2. σ electons: in single bond between C-H and C-C atoms.
3. n electrons: not involved in bonding. Compound containing N,O,S halogens may absorb
UV radiation.
Type of electronic transition:
Energy of the various transitions follow the order.
n → ∏* < ∏→ ∏* < n→ σ*< σ → σ*
1. σ → σ* transition: eg. Saturated hydrocarbon, energy-high, occur in far UV region at
shorter wavelength (125-135 nm)
2. n → σ * transition: contains one heteroatom like N,S,O,halogen eg. Methyl chloride173 nm, methyl iodide-258 nm, lower energy than σ → σ* occur at longer wavelength.
3. ∏→ ∏* transition: contain at least one multiple bond, intermediate energy between
σ → σ* and n → ∏* transitions. eg. In carbonyl compound ∏→ ∏* transition-180 nm ,
ethylene absorbs in UV region and exhibit two bands. One band (intense)-174 nm, second band
(weak)- 200 nm.
4. n → ∏* transition: unsaturated molecule contain N, S,O, halogen, least energy, max
wavelength eg. Aldehyde and ketone show two type bands, one occur at lower energy
another at high energy.
Chromophore: Any isolated covalently bonded groups that shows a characteristics
absorption in UV or visible region irrespective of the fact whether colour is produced
or not .
Type of chromophore:
1. Which contain ∏ electrons undergo ∏→ ∏* transicon
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2.Which contain both ∏ and n electrons undergo ∏→ ∏* and n → ∏* transition eg.
Nitriles (C N) - 165 nm (n-∏*)
Auxochromes: are auxillary groups which do not show any characerstics absorption above
200 nm but which when attached to given chromophore causes a shift of absorption band
to longer wavelength with increase in intensity of absorption band are called
auxochromes. Eg. OH, NH2, SH and their derivative such as –OR, -NHR,-NR2, -SR and some
of halogen.
Application of UV-Vis spectroscopy:
1. In qualitative analysis 2. Detection of functional group 3. Extent of conjugation 4. In
quantitative analysis 5. In the detection of impurities 6. In chemical impurities.
Flame photometry: referred to as flame emission spectroscopy. It involves the analysis of
metal present in a sample on the basis of radiation emitted by it when the sample is atomized
into a flame.
i.
ii.
iii.
Aspiration of liquid sample (containing ) metal into flame
The solvent get evaporated leaving behind particle of salt
The salt get vaporized and dissociates/decomposition into its constituent
atoms.
Some of the metal atom get excited to higher energy levels.
The excited atoms emit radiation characteristic of metal atom.
iv.
v.
M+X-(aq)
Aspiration
M+X-
Evaporation
Voparization
MX(s)
MX(g)
Emission
*
M
Excitation
Decomposition
& Reduction
M
M(g) + X(g)
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Applications:
1. It is used for the analysis of Na, K, Ca, Cu, Li,Cs, Rb, Sr, Ba,Cr, Ag, Zn
2. In Industries, it is useful for the detection of element in cement, glass, fuel, soil, natural
waters, plant material, biological fluids.
3. In medical science, it is used for analyzing the blood and urine sample.
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