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CHEMISTRY-II
Organic and Physical Chemistry

Dr. J. N. Gurtu
MoSc., Ph.D..
Retd. Principal,

Meerut College, Meerut.

Dr. H. C. Khera
M.Sc., Ph. D.

Reader & Head,
Chemistry Department,

loP. College, Bulandshahr.

»

PRAGATI PRAKASHAN


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PRAGATI PRAKASHAN
Educational Publishers

HeaiOifice:

PRAGATI SHAWAN,

240, W. K. Road, Meerut-250 001
Tele Fax: 0121-2643636, 2640642,
SMS/Ph. : 0121- 6544642,6451644
www.pragatiprakashan.in
e-mail:

First Edition: 2009

Regd. Office:

ISBN:

978-81-83986-47-3

New Market, Begum Bridge.
Meerut-2S0 00 1
Phone: 0121-2661657
Published by : K.K. Mittal for PRAGATI PRAKASHAN, Meerut-250001. Visit us at :
www.pragatiprakashan.com. laser Typesetting: Devendra K. Tyagi (Mob. 9719000944) Meerut.
Printed at. Arihan, Electric Press, Meerut


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1. ORGANIC CHEMISTRY AND PURIFICATION OF ORGANIC COMPOUNDS 1-1 ~

Organic chemistry 1
Requirement and methods of purification 2

Tests of purity 10
Chromatography 12
Exercises 13
2.

OUALITATIVE AND OUANTITATIVE ELEMENTAL ANALYSIS

16-'J6

Qualitative detection of elements 16
Quantitative estimation of elements 19
Exercises 32
}.

EMPIRICAL, MOLECULAR AND STRUCTURAL FORMULA,
MOLECULAR MASSES OF ORGANIC COMPOUNDS
Empirical formula 37
Molecular formula 39
Molecular weight of organic acids and bases 39
Numerical problems based on empirical, molecular and structural formulae 42
Exercises 52

4. TETRAVALENT CHARACTER OF CARBON, FUNCTIONAL GROUPS AND
NOMENCLATURE OF ORGANIC COMPOUNDS
Tetrahedral concept of carbon atom 53
Functional groups 54
Nomenclature of organic compounds 55
Exercises 72
~.


SATURATED HYDROCARBONS, ALKANES OR PARAFFINS

n-8}

84-94

Alkanes or paraffins 84
Nomenclature of alkanes 84
General methods of preparation of alkanes 85
General properties of alkanes 88
Exercises 92
6.

UNSATURATED HYDROCARBONS (ALKENES AND ALKYNES)
Alkenes or olefins 95
Nomenclature of alkenes 95
General methods of preparation of alkenes 96
General properties of alkenes 98
Alkynes or acetylenes 103
Nomenclature of alkynes 103
General methods of preparation of alkynes 104
General properties of alkynes 105
Acidic nature of hydrogen in acetylene 109
Ascent and descent of alkane series and important conversions 110
Exercises 111

7.

HALOGEN SUBSTITUTED ALKANES
Monohalogen derivatives of alkanes 115


9~-114

l1~-no


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Ethyl bromide or bromoethane 119
Dihalogen derivatives of alkanes 122
Trihalogen derivatives of alkanes 123
Chloroform (Trichloromethane) 123
Exercises 128
8.

ORGANOMETALLIC COMPOUNDS AND GRIGNARD'S REAGENT
Organometallic compounds 131
Exercises 143

111-14'J

9.

PREPARATION, PROPERTIES AND USES OF COMPOUNDS

144-161

(Ethanol, Glycol and Glycerol)
Alcohols 144
Ethyl alcohol or ethanol 146

Glycols 150
Glycerol 153
Exercises 160
10. ALDEHYDES AND KETONES
Introduction 162
Classification 163
Nomenclature 163
General methods of preparation 164
General properties of aldehydes and ketones 166
Formaldehyde or methanal 176
Acetaldehyde or ethanal 177
Acetone or propanone or dimethyl ketone 180
Exercises 181

162-18)

11. MONOCARBOXYLIC ACIDS AND THEIR DERIVATIVES
Carboxylic acids 185
Carboxylic acid derivatives 194
Acid anhydrides 195
Acid halides 197
Acid amides 200
Acid esters 202
Exercise& 206

184-207

12. DICARBOXYLIC AND TRICARBOXYLIC ACIDS

208-222


Malic acid 208
Tartaric acid 209
Oxalic acid or ethanedioic acid 213
Maleic acid 215
Fumaric acid 217
CItric acid 217
Exercises 221
ll. UREA
Exercises 226

221-227


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14. ISOMERISM
Explanation and definition of isomerism 228
Types of isomerism 228
Exercises 238

228-240

1~.

241-2~8

STRUCTURE AND BONDING
Hybridisation 241
Bond length 243

Bond angle 244
Bond energy 245
vander Waals interactions 247
Resonance 248
Hyperconjugation or no bond resonance 250
Inductive effect 253
Hydrogen bonding 256
Exercises 257

16. ARENES AND AROMATICITY
Aromatic hydrocarbons or arenes 259
Benzene 259
Constitution of benzene 265
Aromaticity 269
Huckel's (4n + 2) rule 270
Exercises 271

2~9-271

17.THERMODYNAMICS
Basic definitions 272
Energy 276
Internal energy 276
First law of thermodynamics 277
Heat changes 278
Heat content or enthalpy 278
Heat capacity of system 279
Spontaneous and non-spontaneous processes 280
Second law ofthermodynamics 281
Concept of entropy 282

Exercises 285

272-286

18. NUCLEAR CHEMISTRY
Nucleus 287
Isotopes 287
Isobars 289
Isotones 290
Natural radioactivity 290
Artificial disintegration or transmutation of atoms 293
Artificial radioactivity 294
Detection and measurement of radioactivity 295

287-l08


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Radioactive decay as first order reaction 298
Binding energy 300
Nuclear reaction equations 301
Nuclear fission (atomic fission) 302
Nuclear fusion (atomic fusion) 303
Transuranic elements 304
Applications of radioactivity and radioisotopes 304
Exercises 307
}09-}40
CHEMISTRY PRACTICALS
Volumetric analysis 311

Types oftitrations 316
Exp. 1. To prepare N/10 standard solution of ferrous ammonium sulphate and
find out the strength of the supplied ferrous ammonium sulphate using
potassium permaganate solution as an intermediate solution.
317
Exp.2. To prepare N/10 standard solution of oxalic acid and find out the
strength of the given oxalic acid solution by using potassium
permanganate solution as an intermediate solution.
318
Exp.3. To prepare N/30 standard solution of ferrous ammonium sulphate and
find out the strength of supplied ferrous ammonium sulphate solution by
319
using K2Cr207 solution as an intermediate solution.
Exp.4. To prepare N/30 standard solution of ferrous ammonium sulphate and
find out the strength of the given ferrous ammonium sulphate solution
by using K2Cr207 solution as an intermediate solution (internal
320
indicator)
Exp.5: To prepare N/30 standard solution of potassium dichromate and find out
the strength of given potassium dichromate solution using ferrous
ammonium sulphate as an intermediate solution (internalindicator).
321
Exp.6. To prepare N/30 copper sulphate solution and find out the strength of the
given copper sulphate solution by titrating it with sodium thiosulphate
solution iodometrically.
322
Exp. 7. To prepare N/30 K2Cr207 solution and find out the strength of the given
K2Cr207 solution by titrating it against sodium thiosulphate solution
iodometrically.
324

PHYSICAL CHEMISTRY EXPERIMENTS
l26
Surface tension 326
Exp. 1. To find the surface tension ofthe given liquid by drop number method at
room temperature.
328
Viscosity 329
Exp.2. To find the relative and absolute viscosity of the given liquid at room
temperature.
331
Thermochemistry 332
Exp.3. To find the water equivalent of a calorimeter.
333
Exp.4. To find out the heat of neutralisation of sodium hydroxide and
hydrochlOrIC acid.
334
Solubility 337
Exp. 5. To determine the solubility of potassium nitrate at room temperature
and also to draw its solubility curve.
339


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CHAPTER 1

ORGANIC CHEMISTRY AND
PURIFICATION OF ORGANIC COMPOUNDS
ORGANIC CHEMISTRY


The term organic signifies life. Berzelius in early nineteenth century proposed
'vital force theory', according to which organic compounds could be obtained from
sources containing life, i.e., from living organisms, e.g., animals and vegetable
sources.
However, in 1828, Wohler, a German chemist gave the first blow to the vital
force theory. He prepared the first organic compound, urea (a compound present
in the urine of animals) in laboratory by heating a mixture of ammonium sulphate
and potassium cyanate.
(NH4)2S04
+
2KCNO
---7
2NH4CNO + K2S04
Ammonium sulphate

Potassium cyanate

NH4CNO

Ammonium cyanate
---7

NH 2CONH2
Urea

The work did not at once disturb the belief in vital force theory. But the
synthesis (preparation of compound from its elements) of acetic acid by Kolbe in
1845, gave the final blow to vital force theory. Soon after, methane was also
synthesised by Berthelot in 1856, therefore, the term organic lost its original
significance.

It was Lavoisier who showed that carbon was the essential element of organic
compounds. Accordingly, organic compounds are now defined as 'the compounds of
carbon' and organic chemistry as the study of these compounds.
[I] Justification for Separate Study
The reason to study compounds of carbon separately, coming under the heading
of organic compounds, is the large number of their typical characteristics.
At present, over two million organic compounds are known and each year the
number of new organic compounds discovered or synthesised, sometimes exceed
the total number of compounds of all the remaining elements (nearly 75,000 are
known), This provides sufficient justification for their study as a separate branch
of chemistry.
[II] Characteristics of Organic Compounds
(i) All the organic compounds are covalent compounds.
(ii) The carbon present in organic compounds is always tetravalent, i.e .•
tetracovalent.
(iii) Unlike inorganic compounds, most of them are insoluble in water.


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2

CHEMISTRY-II (BIOTECH.)

(iv) Most of the organic compounds possess low m.p. or b.p. as compared to
inorganic compounds.
(v) Perhaps the most important characteristic property is the phenomenon
of 'isomerism', which may be defined as "when two or more compounds
possess the same molecular formula but differ in their properties". Such
compounds are called 'isomers' and the phenomenon as 'isomerism'. The
phenomenon of isomerism is exhibited by organic compounds due to their

highly directional covalent bonds.
(vi) Another characteristic of organic compounds is the presence of
'catenation property', actually a property of carbon, which means the
tendency to link together. The carbon atoms unite with each other by all
possible means including linking through single, double or triple bonds,
forming straight or branched chains or cyclic compounds. It is this
property of carbon which is mainly responsible for such a large number
of organic compounds known.
REQUIREMENT AND METHODS OF PURIFICATION

[I] Requirement of Purification
Since most of the organic compounds are isolated from natural sources where
they are present along with other organic compounds with identical properties, it
is essential to purifY them before subjecting them to qualitative and quantitative
analysis. Unlike inorganic compounds, the purification of organic compounds is
tedious as large number of them decompose on heating, are sensitive to other
reagents and resist the solvent action of water.

[II] Methods of Purification
Separation and purification of organic compounds depend mainly on the
difference of physical properties of organic compounds. The main methods of
purification of organic solids and liquids are as follows :

(1) Purification of Organic Solids
(i) S'imple crystallisation
This method is used to purify those organic compounds which are mixed either
with insoluble impurities or less soluble impurities.
Principle: Each organic compound is more soluble in a particular solvent at
higher temperature but less soluble at lower
temperature.


The process includes the preparation of a
saturated solution of the solid at a higher
temperature and then separating the solid in pure
form by cooling the solution.
The method is also employed in inorganic
chemistry. The only difference in the case of organic
compounds is the use of various organic solvents,
e.g., alcohol, benzene, ether, acetone, chloroform
etc., apart from the use of water. The success of the
method depends upon the selection of suitable
solvent. A good solvent must have low boiling point

Fig. 1. Hot water funnel


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ORGANIC CHEMISTRY AND PURIFICATION OF ORGANIC COMPOUNDS

3

Whatman
tilter paper

~~:=~

Trap.

Fig. 2. Filtration by using filter pump


and easy vaporisation. Moreover, the solid to be purified should be more soluble
at high temperature but less at a low temperature so that cooling should lead to
crystallisation.
Method : The crystallisation of an organic solid involves the following
procedure:

A saturated solution ofthe solid to be purified is prepared at high temperature.
It is decolorised, if necessary, by heating or refluxing with animal charcoal, and
filtered while hot through a hot water funnel (Fig. 1) using filter pump (Fig. 2). A
hot water funnel is·an ordinary funnel surrounded by a double walled copper jacket
between which hot water is filled. This keeps the funnel hot and thus prevents
cooling and consequent crystallization of the solid over the filter paper during
filtration.
The filtrate is then allowed to cool in a shallow container when pure solid starts
depositing in the form of crystals leaving behind impurities in the mother liquor.
Crystals thus obtained are separated by filtration or by centrifuging. Filtration is
generally done on a Buchner funnel applying a little
vacuum by using a filter pump (Fig. 2) to expedite the
procedure.
Normally, after the first filtration, the crystals,
separated on filter paper, are washed once or twice by
the same solvent in order to remove any adhering
impurity. Crystals thus obtained may further be
purified by recrystallisation.
Crystals of pure compound are kept in a vacuum
desiccator (Fig. 3). A vacuum desiccator differs from
an ordinary one in that it has on the top a tube which
is connected to a suction pump to suck out the air from
desiccator.


Fig. 3. Vacuum desiccator


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4

CHEMISTRY-II (BIOTECH.)

(ii) Fractional crystallisation
The method is used to purify those organic compounds which are mixed with
impurities soluble in a particular solvent along with the organic compound but
have different solubilities.
Principle: A saturated solution of a mixture of two compounds with different
solubilities in a particular solvent is prepared at a higher temperature. On cooling
slowly, the compound with tess solubility in the solvent crystallises out first.
The method is used for the separation of a mixture of two or more solids which
are soluble in the same solvent but at different temperatures.
Method: In this method, the saturated solution of the mixture is prepared in
hot solvent and then, after decolorisation and filtration, it is subjected to gradual
cooling. The various fractions obtained at different temperatures are separated
from time to time. The method can be easily understood by the following example.
Suppose two solids 'N WId 'B' are present in a mixture. Both are soluble in the
same solvent but '/I: is more soluble than 'B'. A saturated solution of the mixture
is prepared in hot solvent, decolorised and filtered. The hot filtrate is then allowed
to cool down slowly, when the less soluble 'B' separates first along with small
quantity of 'No This bunch of crystals is separated. Further cooling leads to
crystallisation of more soluble solid 'N alongwith a small quantity of'B'. This bunch
of crystals is also separated. Then these two bunches of crystals are furher
subjected to fractional crystallisation separately. The process is repeated several

times till the separation is complete.

(iii) Sublimation
Normally, a solid, when heated, first melts into a liquid and on strong heating,
is changed into vapours and vice versa on cooling. However, there are certain solids
which on heating directly go into vapour state and on cooling vapours form the
Bolid. This phenomenon is called sublimation.
Heat

Solid....

">

Vapour

Cool

Principle: Like liquid compounds, solid compounds also have vapour pressure
though it is low. A solid on heating absorbs energy
Cotton
A layer of wet
equivalent to its latent energy of sublimation. This
plug
filter paper or
results in a sudden rise in the kinetic energy of
cloth
molecules which directly go to vapour state
without passing through the liquid state.
This property of sublimation is found very
useful in purification and separation of those

compounds which possess it. Generally, the
ap:==~IrIIlI:I;d~.rAsbestos
method is used to purify a solid which sublimes,
from other compounds which do not sublime. A few
examples
include
naphthalene,
camphor,
anthracene, anthraquinone, benzoic acid etc.
Method : The procedure involves heating of
impure compound in a porcelain dish covered with
a perforated asbestos sheet on which a funnel is
inverted (Fig. 4). The walls of the funnel are kept
Fig. 4. Sublimation


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ORGANIC CHEMISTRY AND PURIFICATION OF ORGANIC COMPOUNDS

5

cool from outside with the help of a wet cloth. The solid, which sublimes, changes
into vapours which, on coming in contact with cooled walls of funnel, condense and
deposit on it in the form of pure crystals.

(iv) Extraction by solvents
This method involves dissolution of organic solid compounds present in plants
or mixed with other solids, in a suitable solvent, filtering it off and removing the
solvent finally by evaporation or distillation. The method is discussed under
following three heads for clear understanding.

(a) Separation of organic solids mixed with inorganic solids: Most of
the organic solids are insoluble in water but soluble in organic solvents, while
inorganic solids are insoluble in organic solvents but soluble in water. Therefore,
such a mixture is shaken with suitable organic solvent, e.g., chloroform, ether,
benzene etc. It is filtered to remove insoluble inorganic compounds. Finally, the
solvent is distilled off from the filtrate to get the solid organic compound.
The reverse of his process is also
applied sometimes, i.e., the inorganic
compounds are removed by shaking the
mixture with water or dilute acid in which
they are soluble. Organic solid is then
obtained by filtration.
Soxhlet extraction : As the organic
compound to be separated may not be
completely soluble in a solvent at room
temperature, the mixture has to be heated
with organic solvent. This is done in a
special apparatus known as 'Soxhlet
extractor' (Fig. 5). The apparatus consists
of a strong wide tube 'C' with a side tube
'T' on the left hand side a siphon tube '8' on
the right hand side and a water condenser
fitted at the top of the wide tube.
The solid mass is taken in the wide
tube. A suitable solvent is taken in the
flask and heated on wire gauze or sand
plate. When the solvent of the flask boils,
its vapours ascend through the side tube
'T' and pass through water condenser
where they get condensed. The hot

condensed solvent drops fall on the solid
mass placed in the wide tube and dissolve
out its soluble constituents. As the level of
the solution in the wide tube rises above
the height of siphon tube, it comes out
through the siphon tube into the flask
containing solvent. The process continues
and more and more of the soluble
constituent passes in solution is collected
in the flask. The solid is then obtained, as
usual, by distilling off the solvent.
Fig. 5. Soxhlet extractor


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6

CHEMISTRY-II (BIOTECH.)

Soxhlet extraction is the best method to extract alkaloids, essential oils from
flowers and leaves and other products.
(b) Separation of organic solid mixed with other organic compounds:
A mixture consists of more than one organic solid and is shaken with different
organic solvents one by one. After each shaking, the solutiOli is filtered. The
different filterings are collected separately. Separate distillation of each provides
different organic compounds.
(c) Separation of organic compound from its solution or suspension in
water: To separate an organic compound from its solution
or suspension in water, organic solvents are used which

dissolve organic compounds but are themselves immiscible
with water, e.g., ether, benzene, chloroform, carbon
tetrachloride etc. For such separation, perhaps the best
solvent is ether for two reasons. First, it is a very good
solvent for most of the organic compounds and second, it is
inactive in nature.
This method uses a separating funnel (Fig. 6). The
separating funnel is half filled with the solutioil or
suspension of organic compound in water. Now, the organic
solvent selected for the purpose is added. After shaking
vigorously, it is allowed to settle down till two layers, one
of water and the other of solvent separate out. The solvent
Fig. 6. Separating
layer containing the organic compDund is collected
funnel
separately from the aqueous layer. The remaining aqueous
layer is again subjected to above treatment with a fresh quantity of organic solvent.
The solvent layer is then kept over anhydrous calcium chloride, which absorbs any
water present. Finally, it is filtered and the solvent is distilled off when the pure
organic compound is obtained as residue.

(2) Purification of Organic Liquids
(i) Simple distillation
Principle: Conversion of an organic liquid into vapours, sending vapours to
other place and condensing the vapours back to liquid is known as distillation.
The method may, therefore, be divided safely into two processes, one of
vaporisation and the other of condensation.
Distillation =Vaporisation + Condensation
The method is suitable to separate or purify an organic liquid mixed with solid
impurities or liquid impurities widely differing in boiling points (more than 40°C).

The simple distillation apparatus (Fig. 7) consists of a distillation flask with a
side tube, in which the impure liquid is taken. Attached to the side tube is a Liebig's
condenser, the other end of which is connected to a receiver to collect the distilled
liquid. Distillation flask generally carries a thermometer fixed through a cork.
Sometimes, glass beads are also added to the flask to prevent bumping of liquid.
Method: The distillation flask is half filled with impure liquid and is heated.
Vapours formed are passed through the condenser and the liquid obtained is
collected in a receiver.
In case the liquid boils below 100°C, a water bath is used, otherwise a sand
bath is advisable. If the boiling point of the liquid to be distilled is above 150·C,
air condenser should be used in place of Liebig's condenser.


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ORGANIC CHEMISTRY AND PURIFICATION OF ORGANIC COMPOUNDS

7

. Thermometer

Air condenser

'~================
---_/Fig. 7. Simple distillation

(ii) Fractional distillation
If the mixture consists of liquids with a difference of 15·C to 40·C in their
boiling points, fractional distillation is the ideal method, provided that none of
the liquids present decomposes at its b.p.


Principle: (i) The boiling point of a mixture of two miscible liquids is always
in between the boiling points of the two liquids.
(ii) The vapours obtained at the boiling point of the mixture have higher
content of the vapours of low boiling liquid.
(iii) As the vaporisation of mixture increases, the boiling point of the mixture
also goes higher.
The above principle is based on Raoult's law.
The apparatus used for this purpose is similar to that of simple distillation
except that a fractionating column containing a side tube is introduced between
the ordinary flask and the Liebig's condenser (Fig. 8). There are several types of
fractionating columns used. A fractionating column is a long tube of wide bore
blown into a series of bulbs, either spherical or pear shaped. Alternately, the tube
is filled with glass beads or broken glass tube (Fig. 9). The actual purpose of a
fractionating column is to increase the cooling surface and to provide obstruction
to the passage of ascending vapour or descending liquid.
Method: To follow the process exactly, let us consider, for example, a mixture
of two liquids 'N and 'B' with boiling points 56°C and 78°C, respectively. The
mixture is heated in a flask fitted with a fractionating column and a Liebig's


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8

CHEMISTRY-I! (BIOTECH.)

Fig. 8. Fractional distillations.

Fig. 9. Fractionating
column.


condenser. The vapours consisting more of 'A: than 'B' rise up the fractionating
column. Here, due to large cooling surface, vapours of'B' condense while those of
'A: pass over and collect in the receiver. As the condensed vapours (liquid),
consisting mostly of the less volatile constituent 'B', flow down the fractionating
column into the flask, they meet the fresh and hot ascending vapours. During this
process, the more volatile component 'A:, if present in the downward flowing liquid,
vaporises again taking the required heat from the ascending vapours of less
volatile 'B'. This results in the condensation of the vapours of 'B' which join the
downward flowing liquid. On the other hand, more vapours of more volatile liquid
'A; ascend through the fractionating column to reach the receiver. This process is
repeated at each point of the fractionating column with the result that by the time
the vapours reach the top ofthe fractionating column, they consist mainly ofm0re
volatile component 'A:, while the downward flowing liquid mainly consists of the
less volatile component 'B'. The liquid collected in the receiver and left in the flask
may again be subjected to the above process separately, to ensure complete
separation.
Fractional distillation in industries is carried out using carefully designed
(according to need) big fractionating columns, e.g., separation of alcohol from water
is carried in a special type of fractionating column called "Coeffy still". Separation
of various components of petroleum is also carried out using a special type of
fractionating column.

(iii) Vacuum distillation or reduced pressure distillation
Many organic liquids decompose at their boiling points. Thus, they cannot be
purified by distillation under atmospheric pressure. Such compounds are,
therefore, purified by distillation under reduced pressure. A common example is
glycerine. Glycerine decomposes much below its boiling point of 290·C. However,
at 12 mm it boils at 180·C and can be safely distilled.



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ORGANIC CHEMISTRY AND PURIFICATION OF ORGANIC COMPOUNDS

9

Principle: The boiling point of a liquid is the temperature at which its vapour
pressure becomes equal to atmospheric pressure. Hence, by reducing the
atmospheric pressure we can lower the boiling point of the liquid. Thus, the boiling
point of a liquid, which decomposes at its boiling point, can be lowered to such a
temperature at which it does not decompose.

Manometer

Fig. 10. Vacuum distillation

Method: As the chances of super heating and bumping are greatly increased
in distillation under reduced pressure, a special type of distillation flask, known
as Claisen flask, is used to minimise this effect. The Claisen flask (Fig. 10) has
two necks, one of which carries a thermometer and consists of a side tube. The
other neck carries a capillary tube partially closed at the top by a pressure tubing
screw-clip arrangement, through which air can be regulated (this checks super
heating). The side tube of the first neck is connected to a Liebig's condenser and
a receiver. Receiver is attached to a vacuum pump to lower the pressure which is
registered by a manometer.
Reduced pressure distillation is used not only to avoid decomposition but it
also serves to economise the fuel in industries. A common example is the
evaporation of sugarcane juice in vacuum pans in the sugar industry.
(iv) Steam distillation
This method is used to purify those organic compounds (solids or liquids) which

are (;) immiscible with water, (ii) possess a high molecular weight, and (iii) have
a fairly high vapour pressure around 100°C, e.g.,o-nitrophenol, aniline,
nitrobenzene etc. Steam distillation is also used in case of compounds which
decompose at their boiling points. However, the impurities present should be
non-volatile.
Principle: The boiling point of a liquid is the temperature at which its vapour
pressure becomes equal to atmospheric pressure. In steam distillation, the vapours
of liquid and water both are present. The two together can become equal to
atmospheric pressure at a temperature which will be lower than the t~mperature
at which either the liquid or water boils.


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CHEMISTRY-II (BIOTE:CH.)

10

Let PI be the vapour pressure of pure water and P2 that of the liquid. The
mixture will boil at that temperature at which PI + P2 = atmospheric pressure
P, e.g., aniline, with a boiling point 184°C, boils in steam at 98.5°C, as the vapour
pressure of water at 98.5'C is 717 mm and that of aniline is 43 mm [So, 717 mm
+ 43 mm = 760 mm, the atmospheric pressure].
Method: The apparatus (Fig. 11) consists of a round bottom flask, which on
one side is attached to a steam generator through a bent tube and on the other
hand is connected with Liebig's condenser through another bent tube by using a
two hole cork. The compound to be purified is taken in the flask, clamped at an
angle to prevent the substance from being splashed into the condenser. The tube
from the steam generator is dipped deep into the impure liquid. Now, water is
boiled in steam generator and the steam formed is bubbled through the liquid to
be purified. Flask containing the impure liquid is also heated on a sand bath to

avoid much condensation of steam in it. The boiling of the impure liquid soon starts
and the vapours of organic compound along with steam pass over and get
condensed in the condenser.
Safety
Tube

Fig. 11. Steam distillation

The next step is the separation of organic compound from water. lfthe organic
compound is a solid, it may be separated by simple filtration. In case it is a liquid,
a separating funnel is used for the purpose.
TESTS OF PURITY

Since the presence of even traces of moisture may be enough to affect the
properties of a compound, a wet organic compound cannot be considered as
completely pure.
Drying of solid is generally achieved by first pressing it between the folds of
filter paper and finally by keeping it in a desiccator, preferably vacuum desiccator
containing anhydrous CaCI 2 , which absorbs moisture. Solids with high melting
points and sufficient stability are normally dried in an air or steam oven.
Organic liquids are generally dried by keeping them over some desiccating
agent which does not react chemically with the liquid. Common desiccating agents
include quicklime, anhydrous calcium chloride, anhydrous potassium carbonate,


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ORGANIC CHEMISTRY AND PURIFICATION OF ORGANIC COMPOUNDS

11


fused copper sulphate, solid potassium hydroxide etc. Finally, they are distilled
over with a small quantity of phosphorus penta oxide or sodium.
After drying, it is necessary to test the purity of organic compounds. As the
physical constants of a compound are always sharp and constant, they are used as
criteria of purity. Generally, determination of
melting and boiling point is used as the
criterion of purity, as even traces of impurities
change the melting or boiling point of a
purity is
also
compound.
Sometimes,
ascertained by the specific gravity or refractive
Capacity
index of the compound.
tubc
[I) For Solids
(i) By determination of melting point:
Each pure and dry organic solid possesses a
sharp melting point. Presence of even traces of
impurities
lower
the
melting
point.
Furthermore, the melting point no longer
remains sharp if the solid is impure, i.e., it
melts between a range of temperature.
For determination of melting point, Thiele's
method is used. The apparatus, as shown in

figure 12, is used for this purpose. First of all,
a thin capillary tube, sealed at the lower end by
heating, is filled one-third by the finely
powdered substance. It is then attached to Fig. 12. Melting point determination
thermometer by wetting it from outside with a
little concentrated sulphuric acid. The thermometer is then lowered into Thiele's
tube containing concentrated sulphuric acid.
Thiele's tube is then heated slowly. The exact
temperature at which the opaque solid in the
capillary tube becomes transparent, is the
melting point of the solid. The solid is purified
again by recrystallisation and melting point
is redetermined. No change in the two
melting points confirms the purity of the
compound.
(ii) By mixed melting point : The
purified sample of the substance is mixed
with a little of pure sample and the melting
point of the mixture is determined. If the
melting point of the mixture is the same as
that of pure substance, it confirms the purity
of the sample.

[II] For Liquids
By determination of boiling point:
The purity of liquids is ascertained by their
boiling points. Each pure liquid possesses a
\

Fig. 13. Boiling point detennination



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12

CHEMISTRY-I! (BIOTECH.)

sharp and constant boiling point. If the liquid is available in large quantity, it is
boiled in a distillation flask fitted with a thennometer. The constant temperature
at which the liquid distils over, is its boiling point.
If the liquid is available in small quantity, it is detennined by Thiele's method
(Fig. 13). The liquid is taken in a small fusion tube attached to a thermometer with
a rubber band. A small capillary tube, sealed at the upper end, is inverted in the
liquid and the thennometer is lowered into Thiele's tube containing concentrated
sulphuric acid. The Thiele's tube is then heated slowly. The tempeature at which
a brisk evolution of bubbles comes out from the open end of the capillary tube is
the boiling point of the liquid.
Sometimes, a simplified method is used. A small amount of liquid is taken in
a boiling tube fitted with a thennometer with the help of a cork, so that the liquid
vapours may escape out. The tube is heated until the mercury shoots up in the
thermometer. The temperature at which mercury becomes stationary is the boiling
point of the liquid.
CHROMATOGRAPHY
It is a modern technique used for the
separation of mixture, isolation of compounds
natural sources, purification and
from
identification of the constituents of a mixture
and also in the concentration of product that
occurs in nature in very dilute state.

Principle: Chromatography is based on the
distribution of a mixture between two phases,
one stationary and the other moving.
The mixture is dissolved in the moving phase
which may be a liquid or gas and is passed over
a stationary phase which may be a packed
column or a paper strip. Different constituents of
the mixture migrate at different rates through
the stationary phase. The different rates of
migration depend upon the solubility of the
constituents in the liquid phase and their
adsorption on the stationary phase. Based on the
nature of the stationary and the moving phase,
chromatography may be classified into followiI.g
types.

[I] Adsorption Chromato- graphy (Column
Chromato- graphy)
This method is based on the differential
adsorption of the constituents of a mixtue on
different adsorbents. Important adsorbents
include alumina, silica gel, magnesium oxide,
sucrose etc.
The solvent used to dissolve the mixture
should be non-polar like petroleum ether.

CaCl: tube

~=J~;I


Solvent

Cotton

,'001

SolId
adsorbent

Cotton
.....;.;.......--- wool

Fig. 14. Apparatus of column chromatography.
I


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ORGANIC CHEMISTRY AND PURIFICATION OF ORGANIC COMPOUNDS

13

The apparatus (Fig. 14), consisting of a long glass tube with a stop cock at the
lower end, is packed with a suitable adsorbent. For this purpose, adsorbent is made
into a slurry in the solvent to be used for dissolving the mixture. It is then poured
into the glass tube. The adsorbent settles down while the excess of solvent is
allowed to flow down through the stop cock.
Now, a concentrated solution of the mixture to be separated, is prepared and
introduced on the top of the adsorbent. As the solution runs through the adsorbent,
the components of the mixture are left behind at different distances depending
upon their solubilities in solvent and their rates of adsorption on the adsorbent.

The layers of the adsorbent with different components of the mixture are called
zones, bands or chromatograms. Zones or bands may possess different colours.
Finally, pure solvent is allowed to run through the adsorbent, which carries along
with it the components adsorbed at different distances, one by one, out of the tube.
This process has been named as elution. The solution flows down through the stop
cock with each disappearing band being collected separately in different receivers.
They are then concentrated and crystallised separately.
Sometimes, the adsorbent column as a whole is pushed out of the tube and
different bands are cut down separately. These sections of adsorbent are then
dissolved separately in suitable solvents. Insoluble adsorbent is then removed by
filtration and the pure components are obtained by crystallisation. This process is
generally used when the components form colourless bands so that they may be
treated with some reagent to obtain coloured bands, e.g., amino acids obtained by
hydrolysis of proteins are sprayed with ninhydrin when they give blue colour.

[III] Thin Layer Chromotography (TLC)
It is a special type of adsorption chromatography in which a glass strip coated
with a thin layer of adsorbent is used as the stationary phase instead of a column.

EXERCISES
[I] Long Answer Type Questions
1. Describe with diagram the steam distillation method of purification of organic
compounds.
2. A liquid mixture has two components - methyl alcohol (B.P. = 65'C) and acetone (B.P.
= 56'C). Describe a method for their separation.
3. Boiling points of two liquids have a difference of W'C. Describe with diagram the
method for their separation.
4. Describe purification of organic compounds with steam distillation method giving
diagram. In which condition is this method used?
5. On which principle is steam distillation based? How are organic compounds purified

by this method? Explain with an example. Describe the method with a suitable
diagram.
6. An organic compound is insoluble in water but is steam volatile.l Describe the method
of its purification with a diagram.
7. Give a method of purification of organic compounds, which decompose at their boiling
points.
8. On which principle fractional distillation is based? Describe the method with diagram.
9. What is the importance of fractional distillation in the purification of organic
compounds? Explain with an example.


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CHEMISTRY-II (BIOTECH.)

10. How is the purity of an organic compound determined ? Explain adsorption
chromatography with an example.
(Meerut 2007)
11. Write a note on 'tests of purity'.
12. Desribe fractional crystallisation method for the purification of organic compounds.
13. What is fractional crystallisation? Explain with a suitable example.
14. What is the importance of steam distillation in purification of organic compounds?
Describe with a suitable example and diagram.
15. Chlorobenzene is water insoluble but is steam volatile. Describe with a diagram the
method for its purification.
16. Glycerine decomposes at its boiling point. Describe with diagram the method for its
purification.
17. What is fractional distillation? Describe the method with diagram.
18. How is an organic compound detected by mixed melting point determination method

? Explain.
19. The difference in the boiling points of two liquids is 15'C. Describe a method to
separate them with a labelled diagram.
20. Write the principle of fractional distillation. Write also the names of any two liquids
which are purified by this method.
21. Describe steam distillation method with diagram for the purification of organic
compounds. Which type of liquids are separated by this method?
22. Describe with a diagram the apparatus used in the distillation under reduced pressure
for the purification of organic compounds. What is the importance of this method in
the purification of organic compounds?
23. On which principle is vacuum distillation method based ? Which type of organic
compounds are purified by this method? Describe it with labelled diagram.
24. Write a note on the following:
(i) Fractional distillation
(ii) Sublimation
(Meerut 2006)
25. Write a note on column chromatography.

[II] Short Answer and Very Short Answer Type Questions
1. How can two immiscible liquids be separated by a simple method?
[Ans. Two immiscible liquids may be separated by using a separating funnell.
2. Generally, which physical constant of an organic solid and a liquid is used to determine
their purity?
[Ans. Melting point or mixed melting point in case of solids and boiling point in case
of liquids are used to test the purity of organic compounds!.
3. How can naphthalene mixed with common salt be purified?
[Ans. Nephthalene may be obtained in pure form by sublimation method].
4. Which method is used to separate aniline from 50% benzene?
[Ans. Aniline may be separated from 50% benzene by fractional distillation].
5. Which method should be used to separate methyl alcohol and acetone from a mixture

of the two?
[Ans. The two components may be separated by repeated fractional distillation when
acetone is collected at 56'C and methyl alcohol at 65'CJ.
6. Which method is used to extract essential oils from flowers, leaves, roots etc. ?
lAns. The method of steam distillation is used].
7. Why water mixed with formic acid cannot be separated by fractional distillation?
[Ans. As the boiling point difference between the two is of only 0.6'C (B.P. of water =
100'C and B.P. offormic acid = 100.6'Cl].
8. Nitrobenzene (B.P. = 211 'C) is immiscible with water (B.P. = 100'C). A mixture of the
two is subjected to steam distillation. Will the temperature at which distillation takes
place between 100' and 211'C, greater than 211'C or less than 100'C ?
[Ans. Less than 100'C].


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ORGANIC CHEMISTRY AND PURIFICATION OF ORGANIC COMPOUNDS

15

9. For a substance to be separated by .......... distilllation, it shdould be .... with water.
[Ans. Steam, insoluble]
10. Give your answer in 'yes' or 'no'.
(i)
Purity of an organic solid is tested by determinatitm of its M.P.
(ii) Vegetable oils are purified by fractional distillation.

(iii) A mixture of aniline and toluene may be separated by chemical method.
(iv) Purification of glycerol is done by steam distillation.
(v)


Soxhlet extractor is used for the separation of organic solids from their mixture.
[Ans. (i) Yes, (ii) No, (iii) Yes, (iv) No, (v) Yes].

000


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CHAPTER 2

.

QUALITATIVE AND
QUANTITATIVE ELEMENTAL ANALYSIS
For investigation and characterisation of organic compounds obtained in a pure
state, it is necessary to subject these to complete molecular diagnosis. The various
steps involved include:
1. Qualitative Analysis
This method includes the detection of elements commonly present in organic
compounds such as carbon, hydrogen, nitrogen, halogen and sulphur. Some
compounds also contain phosphorus and metals.
2. Quantitative Analysis
This method involves the determination of the percentage of various elements
present in organic compounds.
QUALITATIVE DETECTION OF ELEMENTS

[I] Detection of Carbon and Hydrogen
As we know, organic compounds are the compounds of carbon so there is no
need of its detection. However, it may be detected alongwith hydrogen as follows:
Small quantity of organic compound, in which the detection of carbon and

hydrogen is to be done, is taken along with some copper oxide in a hard glass test
tube fitted with a one hole cork. A bent tube with a bulb in its middle, is inserted
into the cork. The other end of the tube reaches inside a test tube containing lime
water. A small quantity of anhydrous copper sulphate is taken in the bulb.
Now the hard glass tube is heated strongly, resulting in the oxidation of carbon
and hydrogen, if present in the compound, to carbon dioxide and water,
respectively. Carbon dioxide produced, turns the lime water milky, while the water
formed, turns the anhydrous copper sulphate blue. The oxidation reactions may
be written as follows:
C + 2CuO ~ CO2 + 2Cu
CO2 + Ca(OH)2 ~
Lime water

CaCOg ..l.

2H + CuO ~ H20 + Cu
CUS04 + 5H 20 ~ CuS04·5H20
Colourless

+ H 20

Calcium carbonate
(white ppt.)

Blue


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QUALITATIVE AND QUANTITATIVE ELEMENTAL ANALYSIS


17

If the organic compound is a liquid or gas, the vapours of compound are passed
over preheated copper oxide. Vapours escaping out are then tested for carbon
'
dioxide and water as usual.

[II] Detection of Oxygen
The detection of oxygen in an organic compound cannot be done by qualitative
analysis. To ascertain its presence, help is taken of quantitative estimation. First
the percentage of all the other elements is determined and if the total of their
percentage is less than 100, it is subtracted from 100. The difference is the
percentage of oxygen in the organic compound.

[III] Detection of Nitrogen, Sulphur and Halogens
The best and the simplest method for testing these elements is Lassiagne's
test.
Lassaigne's solution : A small piece of freshly cut sodium is taken in an
ignition tube. It is heated slightly till the sodium piece shines. Now a small
quantity of organic compound, in which the detection of above elements is to be
done is introduced. The amount of organic compound should be just sufficient to
cover the sodium piece. The ignition tube is heated, first slowly and then strongly,
till it becomes red hot. The tube should always be heated in slanting position
keeping its mouth away from the body with the help of tongs. The red hot tube is
then plunged into about 10-12 ml of distilled water taken in a china-dish or small
beaker. The tube.will break itself. If it does not, it should be broken with a glass
rod. The process is repeated with another ignition tube with fresh quantity of
organic compound and this tube is also dropped into the same distilled water. The
distilled water containing both the broken tubes is boiled for 2-3 minutes and
filtered hot. The filtrate, which should be colourless, is called Lassaigne's solution

or sodium extract.
Principle : Since organic compounds are covalent compounds, they do not
ionise. The elements present in organic compounds have to be converted into
inorganic compounds, i.e., ionic compounds so that the ions formed may be tested.
Heating with sodium produces ionic compounds of the elements present, e.g.,
nitrogen forms sodium cyanide, sulphur produces sodium sulphide and halogens
form sodium halides. The reactions may be written as :
(i) Na + C +
N
~
NaCN
Nitrogen

(ii)

2Na +

S
Sulphur

2Na +

(iii)

Sodium cyanide
~

X2

-~


Cl 2

-~

Br2

-~

Halogen

(a)
(b)

2Na +
2Na +

Na2S

Sodium sulphide

2NaX
Sodium halide

2NaCl
Sodium chloride

2NaBr
Sodium broride


(c)

2Na +

12

-~

2NaI
Sodium Iodide

(iv)

2Na + 2H20 -~ H2 + 2NaOH
Lassaigne's solution (sodium extract) is used to test the elements present by
the following methods :


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CHEMISTRY-II

(~IOTECH.)

(1) Test for nitrogen: To 0.5 ml of sodium extract, 0.5 ml of freshly prepared
aqueous solution of ferrous sulphate and a few drops of sodium hydroxide are
added. The green precipitate so formed is boiled and cooled. Now the green
precipitate so produced is dissolved in minimum quantity of hydrochloric acid [if
sulphuric acid is used in place of hydrochloric acid then a few drops of ferric

chloride should also be added). A green or prussian blue colour of solution confirms
the presence of nitrogen in the compound. Reactions involved in this test, are:
FeS04 + 2NaOH -~ Na2S04 + Fe(OHh
Ferrous sulphate

Fe(OHh

Ferrous hydroxide

+

6NaCN

-~

Sod. cyanide

3Na4Fe(CN)6

+

4FeCl3

Na4Fe(CN)6 +

2NaOH

Sod. ferrocyanide
-~


Ferric chloride

Fe4[Fe(CN)61a +

12NaCI

Ferric ferrocyanide
(Pruss ian blue)

If the organic compound contains both nitrogen and sulphur, a red colour is
formed instead of green or blue owing to the formation of ferric sulphocyanide.
NaCNS
N a + C + N + S -~
Sod. sulphocyanide

3NaCNS + FeCl3 ~

Fe(CNS)3

+ 3NaCl

Ferric sulphocyanide
(Red)

(2) Test for sulphur:
(a) Take 0.5 ml of sodium extract in a test tube. A few drops of freshly prepared
sodium nitroprusside are added. Formation of a purple colour confirms the
presence of sulphur.
Na2S + Na2[Fe(CN)5NO] -~ Na4[Fe(CN)5NOS]
Sod. nitroprusside


Sod. thionitroprusside
(Purple)

(b) In another test tube, take 0.5 ml of sodium extract and add sufficient acetic
acid to make the sodium extract acidic. Then a small quantity of lead acetate
solution is added to this acidic solution. Formation of a black precipitate of lead
sulphide confirms the presence of sulphur.
Na2S + (CH3COO)2Ph ~ PbS + 2CH3COONa
Lead acetate

Lead sulphide
(Black ppt.)

(3) Test for halogens: Halogens (chlorine, bromine and iodine) are tested as
follows:
(a) To 0.5 ml of sodium extract, one or two drops of concentrated nitric acid
are added and heated. This is done to decompose sodium cyanide or sodium
sulphide present in the sodium extract so that they do not interfere with the test
of halogens.
HCNi
NaCN + HN03 ~ NaN03 +
Hydrogen cyanide

Na2S+2~03~2NaN03 +

H 2S i
Hydrogen sulphide

Now, silver nitrate solution is added:

(a) Formation of white precipitate, soluble in ammonium hydrmcide,
confirms the presence of chlorine.