Kufa University
College of science
Practical Organic Chemistry
Second stage
Ass.Tech. Nuha Salman
Ass.Tech. Hawraa Mohammed
Ass.Tech. Hashem Mushtaq
COMMON LABORATORY APPARATUS
1-Beakers :are useful as a reaction container or to hold liquid or solid
samples. They are also used to catch liquids from titrations ,
filtrates from filtering operations and used as distillation receiving
container.
2-Volumetric Flasks : are used to measure precise volume of liquid or to
make precise dilutions.
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3- Erlenmeyer Flasks (conical flask): are useful to contain reactions or to
hold liquid samples. They are also useful to catch filtrates.
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-2-
4-Vacuume Flask (side-arm flask and filtering flask): A type of glass flask
used in a laboratory similar to an Erlenmeyer flask, but with short arm coming
of it used for connect the flask to a vacuum source. The Vacuume Flask is
hold a reduced pressure .note the heavy the walls of this flask they are
designed to withstand
reduced pressure without imploding
this design
feature is the reason for the high cost of this flask
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5- Round bottom flask: Used for distillation or heating of liquid, allows
uniform heating
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6-Round-bottomed flask quic fit one,tow and three nick : used for the
chemichal reactions with different size the tow and three nick used for
inserting thermometer or the condenser reaction or adition of materiales.
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-3-
7-Thermometer :Used for measuring temperature.
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8-Droppers: are for addition of liquids drop by drop.
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9-Pipettes:
are
used
to
dispense
small
quantities
of
liquids
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10-Pipette bulb :Used along with pipette to suck liquid .
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-4-
11- Condenser :Used for condensing volatile liquid during distillation
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12-Fractional column :it is a long tube with big surface area filled with glass
beads used to do multiple times of evaporation and condensation in one time
to separate tow or more liquid in high purity.
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13-Receiving adapter :Used to connect condenser with receiving flask in the
distillation system.
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-5-
14- Distil head:Used for connecting distillation flask with condenser and
thermometer in the distillation system.
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15-Funnel: Used for liquid transfer. Also for simple filtration.
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16- Buchner funnel:Used for vacuum filtration using filter paper.
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17-Separatory funnel: Used for Liquid-Liquid extracts, designed for
increase separation efficiency.
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-6-
18-Graduated Cylinders : Used for measuring liquid with better accuracy
than beaker.
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19- Bunsen burner :Used and heat source.
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20-Hot Plates: can also be used as sources of heat when an open flame is
not desirable.
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21- Test Tubes : are for holding small samples or for containing.
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-7-
22-Test tube holders : are for holding test tubes when tubes should not be
touched.
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23-Tongs: are similar in function to forceps but are useful for larger items.
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24-Wash bottle :is used for dispensing small quantities of distilled water.
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25-Watch glasses: are for holding small samples or for covering beakers or
evaporation dishes.
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26-Stand : Used commonly as base for holding distillation system andburette
along with clamp and boss head.
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27-Clamp: Used for holding glassware along with stand and boss head
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28-Ring stand with Rings :are for holding pieces of glassware in place.
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29-Filter paper: Used for filtration, available with different pore size.
---------- ---------------------------------------------------------------------------------------------
30-Mortar and Pestle :Used for graining materials which have large particle
size to small.
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31-Crucible: Used for burn sample at high temperature.
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-9-
32-Wire gauze: Used for spread the head of burner homogeneously
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33-Spatula: used for weighting of the chemicals and to take and handle small
quantities of solid chemicals.
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- 10 -
Experimental (1):- (Melting Point)
A pure nonionic crystalline organic compound usually has a sharp and
characteristic melting point. A mixture of very small amounts of miscible
impurities will produce a depression of the melting point and an increase in
the melting point range (0.5o – 1o for a pure compound). Consequently the
melting point of a compound is a criterion for purity as well as for
identification.
The melting point of an organic solid can be determined by introducing a
tiny amount into a small capillary tube , attaching this to the stem of a
thermometer centered in a heating bath , heating the bath slowly, and
observing the temperatures at which melting begins and is complete, Pure
samples usually have sharp melting points, for example, 149.5 – 150oC or
189 – 190oC ; impure samples of the same compounds melt at lower
temperatures and over a wide range, for example, 145 – 148oC or 187 –
189oC.
The contaminant that depresses the melting points and extends the
melting range may be an indefinitely characterized resinous material, or it
may be a trace of a second chemical entity of melting point either higher or
lower than that of the major component. Under equilibrium conditions the
temperature at which a pure solid melts is identical with at which the molten
substance solidifies of freezes.
one compound (A) depresses the melting point of another (B) with which
it is mixed. Just as salt lowers the freezing point of water If pure (A) melts at
150 – 151oC and pure (B) at 120 – 121oC, mixtures of (A) with small amounts
of (B) will melt unshapely at temperatures below 150oC and mixture of (B)
containing (A) will melt below 120oC . Both the temperature and sharpness of
melting are useful criteria of purity.
- 11 -
A third substance (C) may have exactly the same melting point as (A) ,
namely 150 – 151oC , but if (A) and (C) are mixed and the melting point of the
mixture is observed, the one substance will be found to depress the melting
point of the other. Depression , or nondepression , of melting point is
invaluable in the identification of unknowns. An unknown (D) found to melt at
150 – 151oC can be suspected of being identical with one or the other known
substances (A) and (C) ; observation that the mixture (AD) shows a melting
point depression would exclude identity with (A) , and failure of (C) to depress
the melting point of (D) would prove (C) and (D) identical.
Apparatus
A variety of different apparatus are available for use in melting point
determination . A very sim ple one is illustrated in figure [1] :
Figure [1] : Melting Point Apparatus
- 12 -
Stand , beaker , rubber , clamp , thermometer , burner , capillary tube ,
triple stand , paraffin wax , boiling stones , sample , unknown substances ,
watch glass , spatula .
Procedure
Using a filter peaper crush the sample to a fine powder on a hard surface
such as watch glass. Push a melting point capillary into the powder and force
the powder down in the capillary by tapping the capillary or by dropping it
through a long glass tube held vertically and resting on a hard surface .
The column of solid should be no more than (2 – 3) mm in height and it
should be tightly packed . The melting point capillary is held to the
thermometer by a rubber ligature . Insertion of a fresh tube under the rubber
band is facilitated by leaving the used tube in place. The sample should be
close to and on a level with the center of thermometer bulb, which must be
fully submerged and centered in the beaker.
If the approximate melting temperature is known, the bath can be heated
rapidly until the temperature is about 20oC below this point, but the heating
during the last 15 – 20oC must be slow and regular . It is important that the
temperature rise no more than 2o per minute while the sample is melting. As
the melting point is approached the sample may shrink because of crystal
structure changed. However , the melting point process beings when the first
drops of liquid are seen in the capillary and it ends when the last trace of solid
disappears. For a pure compound this whole process may occur over a range
of only 0.5o , hence the necessity of having the temperature rise slowly during
the determination.
- 13 -
Experimental( 2):- (Boiling Point)
The boiling point of a compound is the temperature at which it changes
from a liquid to a gas. This is a physical property often used to identify
substances or to check the purity of the compound.
The boiling point of a liquid is important physical property. A liquid boiling
point is the temperatuer when its vapor pressure is equal to the atmospheric
pressure. Normally, the boiling point is measured at one atmosphere (101
kPa or 760 mmHg or 760 torr) . Like melting points boiling point are
characteristic properties of pure materials. Boiling point are approximately
related to their molecular weight , the higher the molecular weight, the higher
the boiling point.
For purposes of this laboratory experiment, the boiling point of an organic
liquid is the temperature range over which the state of the organic compound
changes from the liquid phase to the gas phase at 760 mm of pressure.
The molecules of compounds that exist in the liquid state are relatively
close together. Compared with molecules of gaseous compounds. The close
proximity of molecules in the liquid state allow these molecules to interact via
non-covalent interactions
( dipole-dipole, H-bonding, vander Waals forces). In general these
interactions are favorable and help to hold the molecules together in defined
volume, but still allow free motion or "flow" . Conversely molecules of a
gaseous compound are much farther away from each other and are not
confined to a specific volume by non-covalent interactions (Fig. [1] ). If
enough energy (often in the form of heat) is provided to the liquid, the
molecules begin to move away from each other by "breaking" the noncovalent forces that hold the compound in the liquid state. Thus, the boiling
point is the temperature range over which enough energy is provided to a
liquid compound so that its molecules can separate sufficiently to transform to
- 14 -
a gaseous state by breaking non-covalent forces. Non- covalent bonds are
broken during a change from the liquid phase to the gas phase.
Heat
Fig. [1]: Phase Change f rom Liquid to Gas at Boiling Point Temperature Range
Factors Influencing Boiling Point
Structural features of a compound influence the boiling point increasing or
decreasing the molecules ability to establish and maintain non-covalent
interactions that hold the molecules close together in the liquid state .The
structural features of a compound that influence boiling point are :
A) Polarity : Increased H-bonds, polar covalent bonds changes in a
molecules tend to increase the boiling point. More polar elements in a
molecule increase the total number of dipole-dipole, ion-dipole and Hbonding interactions. More energy (higher boiling point temperature ) is
necessary to break these interactions and allow the molecules to move
away from each other into a gaseous state.
B) Molecular weight : Increased molecular weight increases boiling point.
A higher molecular weight compound has more atoms that can be
involved in non-covalent interactions. The greater the number of noncovalent interactions, the more energy ( higher boiling point
temperature ) that is necessary to break the non-covalent interactions
to transform the compound from the liquid phase to the gas phase.
- 15 -
C) Branching : Branching decreases boiling point. Branching blocks
molecules from packing together too closely. The closer molecules are,
the stronger the non-covalent interactions. Thus molecules that are
forced to be farther away from each other due to branching have
weaker non-covalent interactions. Less energy (lower temperatures) is
needed to change
the phase from the liquid phase to the gas for
branched compounds relative to straight chain compounds. (Fig. below)
Procedure
Immerse the assembly in a water bath (or and oil bath for samples with
boiling point higher than 100oC ) (Fig. 1). As the temperatrure is slowly
increased, a rapid evolution of bubbles from the end of the tube begins.
Continue heating for about 5-10 seconds to be sure that all of the air has
been expelled from the capillary, and the vapors of the liquid remains in the
capillary. When the heat is removed but do not take the assembly out of
water bath (or oil bath), carefully watch the capillary. Bubbles continue to be
seen until the pressure exerted by the vapor of the liquid becomes equal to
the atmospheric pressure. As the temperature decreases, the bubbles will
slow down and as soon as, the liquid rises into the capillary. The boiling point
of the sample is reached when the bubbles stops. Read the thermometer and
record the temperature. The temperature observed when this happens should
- 16 -
be the observed boiling point of the liquid. Compare your experimental result
to the literature value (Table below) of the boiling point for the liquid used. If
your technique is good, your experimental value should not be differ from the
known value (literature value ) by more than 2-3oC. Repeat the procedure
with the known liquids. Each time you perform the procedure,you must use a
new capillary. If will also be necessary to allow the hot bath to cool at least
15-20oC below the suspected boiling point before repeating your experiment.
Fig.1Boiling Point Apparatus
substance
Boiling point(oC)
Pentane
36.1
Hexane
69
Heptane
98.4
Octane
125.7
2-Methylheptane
117.7
3-Methylheptane
119
2,2-Dimethylhexane
106.8
3-Ethylpentane
93.5
2,2,4-Trimethylpentane
99.2
Acetone
56-57
Methanol
65
Ethanol
78-79
Propanol
97-98
2-Propanol(isopropanol)
82-83
Water
100
Cyclohexane
80.7
- 17 -
Experimental (3):- (Recrystallization)
The products of chemical reactions can be impure . Purification of your
products must be performed to remove by-products and impurities . Liquids
are customarily purified by distillation , while solids are purified by
recrystallization (sometimes called simply "Crystallization") .
Recrystallization : is a method of purifying a solid . There are two types of
impurities : those more soluble in a given solvent than the main component
and those less soluble .( if there are any impurities that have the same
solubility as the main component then a different solvent needs to be chosen)
When organic substances are synthesized in the laboratory or isolated
from plants , they will obviously contain impurities . Several techniques for
purifying these compounds have been developed . The most basic of these
techniques for the purification of organic solids is recrystallization , which
relies on the different solubilities of solutes in a solvent .
A good (suitable) recrystallization solvent will dissolve a larg amount of the
impure compound at temperatures near the boiling point of the solvent . Small
amount of compound being purified should remain in the solution at low
temperatures between approximately 25 and -5 0C . Low solubility at low
temperatures minimizes the amount of purified compound that will lose during
recrystallization .
A suitable recrystallization solvent should also be partially volatile in order
to be easily removed from the purified crystals . The solvent should not react
with the compound being purified and it should have the boiling point below
the melting point of the compound being purified because solid melts before
dissolves . In selecting a good recrystallization solvent one should not also
consider flammability , toxicity , expensive and available .
- 18 -
Polar compounds dissolve polar compounds and non-polar compounds
dissolve non-polar compounds. The most commonly used recrystallization
solvents are presented in the following table:
Solvent
Formula
Polarity
Boiling point (0C)
Water
H2O
Very polar
100
ethanol
CH3CH2OH
Polar
78
methanol
CH3OH
Polar
65
dichloromethane
CH2Cl2
Slightly polar
40
diethyl ether
(CH3CH2)2O
Slightly polar
35
Organic compounds with one polar functional group and a low number of
carbon atoms such as methanol , ethanol and n-propanol are highly soluble
(miscible) in water. These alcohols from hydrogen bond with water due to the
polar-OH functional group. As the number of carbons per polar functional
group increase , solubility decreases. The solubility of alcohols with four to
five carbons carbons are given in the following table:
Alcohol
Formula
Solubility(g/100ml H2O)
n-butanol
CH3CH2CH2CH2OH
8
n-pentanol
CH3CH2CH2CH2CH2OH
2
n-hexanol
CH3CH2CH2CH2CH2CH2OH
0.5
n-heptanol
CH3CH2CH2CH2CH2CH2CH2OH 0.1
Compounds with six or more carbons for each polar group will not very
soluble in polar solvents but will be soluble in non-polar solvents such as
benzene and cyclohexane.
- 19 -
Procedure
Using a weighing paper , weigh out about 1.00g of "impure Benzoic acid
for recrystallization " and transfer it to a (125 ml) Erlenmeyer flask . Add
about( 20 ml) distilled water , using a graduated cylinder , to the flask and
bring the mixture to the boiling point by heating on hot plate , while stirring the
mixture and boiling gently to dissolve benzoic acid completely .
Remove the flask from the hot plate and examine the solution. If there are
particles of benzoic acid still undissolved, then add an additional amount of
hot or cold water in small increments and resume heating the solution. The
objective is to dissolve the entire solid in only as much as hot or near boiling
solvent (water) as is necessary. Do not add too much water or the solution
will not be saturated and the yield of purified benzoic acid will be reduced.
Keep adding water in small amounts (several drops at a time from a Pasteur
pipette) until all of the benzoic acid is dissolved and the solution is boiling.
If the solution is completely clear (though not necessarily colorless) and no
solid benzoic acid is visible, then add additional 10-15 ml water to the mixture
and place the Erlenmeyer flask on a countertop where it will not be disturbed
and cover with an upside-down small beaker (to prevent dust contamination).
Allowing the flask to cool slowly will give the best-shaped crystals after about
5-10 minutes. If crystallization does not occur after 10 minutes, scrape the
sides of the flask above the level of the solution with the sharp end of a glass
rod hard enough to audibly scratch the interior surface of the flask. This may
dislodge some undetectable, small crystals that will drop into the solution and
"seed" the solution, helping to induce crystallization. A seed crystal can serve
as a nucleation point for the crystallization process. Cooling the solution in an
ice bath may also help at this point.
When the crystals have formed completely (may required ice bath), collect
your solid chemical by setting up a vacuum (suction) filtration on a properly
- 20 -
fitted filter paper in a clean Büchner funnel apparatus as described by your
instructor. ( Fig 1) :
( Fig 1)
Pour the chilled mixture into the Buchner funnel. The water should filter
quickly - if not, check for vacuum leaks. Get all the crystals out of the flask
using a spatula or stirring rod. Rinsing with 1 or 2 mLs of cold water helps get
the crystals out of the flask, and rinsing helps remove impurities.
Let the aspirator run for a few minutes to start air-drying the crystals. Then
use a spatula to lift the filter paper and crystals out of the Buchner funnel,
then press them as dry as possible on a large clean paper towel (hand dry),
allow them to dry completely, and transfer the dry sample to a pre-weigh
weighing paper. Determine the weigh the DRY crystals of recovered benzoic
acid.
Calculate the percent recovered using the following written formula and
determine the melting point of your recrystallized benzoic acid.
Weight of benzoic acid obtained after recrystallization
% Recovered
=
Weight of benzoic acid before recrystallization
- 21 -
Experimental (4):- (Sublimation)
Sublimation is the
process whereby a solid evaporates from a warm
surface and condenses on a cold surface , or the direct conversion from solid
state to gas state without passing with liquid state . Sublimation is an
endothermic phase transition that occurs at temperatures and pressures
below a substance,s triple point (is the temperature and pressure at which
three phases ( for example , gas , liquid and solid ) of that substance coexist
in thermodynamic equilibrium) it is a technique used to purify a solid
compound.
This process is of special value when it is desired to separate a solid which is
volatile from substances which do not vaporize readily. It generally yieldes a
very pure substance in organic chemistry this process is used to purify
quinones , iodine and naphthalene , benzoic acid and camphor . The success
of the method depends upon the compound having a high enough vapour
pressure at temperature below the melting point so that the rate of
vaporisation from solid will be rapid and the vapour may be condensed back
to the solid upon a cold surface. The yield of sublimate will be greatly
improved if the sublimation is carried out under reduced pressure, and further
under these conditions the lower temperature employed reduces the
possiblity of thermal degradation. Substances having low vapour pressures at
their melting points can only be sublimed under greatly diminished pressures
(10-3 to 10-6 mmHg).
It preferred over crystallization when the amount of material to be purified
weighs less than 100 mg. Impurities should have different vapour pressures
then the substance to be purify so that they may be either removed with initial
sublimate or allowed to remain in the residue. A simple from of apparatus
which gives good results is shown in following figure :
- 22 -
Procedure
The process is most easily carried out between crossable and funnal which
is fit each other closely. The substance which has been carefully dried is
placed in the crossable which is covered with a piece of filter – paper, in
which a few small holes have been cut to allow the passage of the vapour
and prevent the back up of the substance to the crossable again and prevent
the escape of vapours. The funnel, placed on the crossable then the
apparatus is heated slowly on a sand-bath or by using weir gause and the
funnel is cooled by putting on it pieces of filter-paper which are kept moist
with cold water.It is necessary to keep the funnel at a temperature lower than
the melting point of the substance to be sublimed. Near the rim. Upon heating
the dish gently the vapour of the pure compound passes through the holes in
the filter paper and condenses on the inside walls of the funnel ; care must be
taken that the heat supply is adjusted so that the funnel does not become
more than lukewarm. An inverted water jacket .
- 23 -
Experimental (5):- (Extraction with solvents)
Extraction is a technique commonly used is organic chemistry to separate
a material you want from those you do not. The process of extraction with
solvents is generally employed either for the isolation of dissolved substances
from solutions or from solid mixtures or for the removal of undesired soluble
impurities from mixtures .
The distribution law or partition law which, states that if to a system of
two liquid layers, made up of two immiscible or slightly miscible components,
is added a quantity of a third substance soluble in both layers, then the
substance distributes itself between the two layers so that the ratio of the
concentration in one solvent to the concentration in the second solvent
remains constant at constant temperature. It is assumed that the molecular
state of the substance is the same in both solvents. If CA and CB are the
concentrations in the layers A and B, then , at constant temperature:
CA/CB = constant = K .
The constant K is termed the distribution or partition coefficient. The
substances commonly used for Extraction are ether, chloroform, ethyl
acetate, petroleum ether…..etc. Organic compounds are usually relatively
more soluble in organic solvents than in water, hence they may be extracted
from aqueous solutions. If electrolytes, e.g. sodium chloride, are added to the
aqueous solution, the solubility of the organic substance is lowered, it will be
salted out : this will assist the extraction of the organic compound.
The problem that arises in extraction is the following. Given a limited
quantity of the solvent, should this be used in one operation or divided into
several portions for repeated extractions in order to secure the best result.
- 24 -
Rules of extraction
1- you must have two insoluble liquid layers to perform an extraction
2- solids must be dissolved in a solvent, and must be insoluble in the other
extracting or washing liquid.
3- If you are washing or extracting an organic liquid, dissolve it into
another liquid, just like a solid, before extracting or washing it.
Procedure
1- Transfer (7ml) of chloroform and (7ml) of 0.1N of NaOH with water to a
separatory funnel.
2- Add (0.2gm) of benzoic acid to last mixture.
3- Shake the mixture for (5min) and have the separatory funnel for periode
to separate two layers without stopper.
4- Transfer the lower layer to conical then add 0.1N of HCl solution
5- Filter the benzoic acid crystals from the solution ,dry it , then weight it.
O
1)
O
H
+
C
NaOH(eq)
+
C
(water insoluble)
2)
C
H
O
O
O
Na
(water soluble)
OH
Na
+ H
+
C
Cl(eq)
O
O
(water insoluble)
(water soluble)
- 25 -
NaCl
OH
Experimental (6):( Isolation of Limonene from Orange peel )
Solid – liquid extraction is often used to extract a solid natural product from a
natural source such as a plant. A solvent is chosen that selectively dissolves
the desired compound , but leaves behind the undesired insoluble solid. A
solid – liquid extraction apparatus , called a soxhlet extractor , is commonly
used in a research laboratory. As shown in figure (I) the solid to be extracted
is placed in a thimble made from filter paper , and the thimble is inserted into
the central chamber. A low boiling solvent , such as diethyl ether, is placed in
the round – bottom distilling flask and is heated . The vapor rises into the
condenser where it liquefies. The condensate (liquid) drips into the thimble
containing the solid. The hot solvent begins to fill the thimble and extracts the
desired product is concentrated in the distillation flask. The product is
concentrated in the flask because the product has a boiling point higher than
that of the solvent or because it is a solid.
( Figure I)
- 26 -
Limonene is a cyclic mono trpines found in orange peel into volatile orange
oil is exist by ratio 90o/o. Limonene is soluble in organic solvents (non polar)
and unsoluble in water.
Limonene properties
Molecular formula: C10H16 (liquid) , Boiling point : 157 – 1800C.
CH 3
H3 C
CH2
Structure formula
Limonene name : 4-Isopropenyl-1-methyl cyclohexene.
Procedure :
We cut the orange peel then put into the central chamber and used benzene
as a solvent is placed in the round-bottom distilling and is heated at 80oC the
hot solvent begins to fill the central chamber and extracts limonene is
concentrated in the distillation flask then benzene is vaporated and remain oil
limonene.
- 27 -
Experimental (7) :-( Fractional distillation)
Purpose :
- purification liquid substance from impurities.
- Resolution a mixture contain two or more liquid substance.
Equipment / Materials :
Hot plate , 125-ml conical flask , column , spatula , condenser , benzene ,
beaker , round , triple stand.
The fractional distillation : Is one of distillation types that used fractional
column with condenser as group , the fractional column is along tube with big
surface area materials , this material must be inert and stable under
distillation condition , as for example glass balls , glass rings tephlone ,
nickrome wire and stainless stell . The fractional column is used to do multiple
times of evaporation and condensation in one time and this decrease number
of distillation operation to separate two or more liquid in high purity . the
purification of liquid by distillation depends on ra,awlts law :
P(Total) = P(A) + P(B)
P(A) in mixture = N(A)
*
Po (A)
N(A) mole fraction, s of (A)
Po(A) vapor pressure of (A)
No. of moles (X)
N(X) = ------------------------------No. of total moles
As for example : mixture of A & B
No. of moles (A)
N(A) = ----------------------------------------------No. of mole A + No. of mole B
- 28 -
P(Total) = N(A) * P0 (A) + N(B) * P0 (B)
Ex : If the mixture of the liquids contain equal amount of benzene and
chlorobenzene , determine vapor pressure for the liquids , and the total
pressure , use vapor pressure of benzene = ( 380 mmHg ) ,
chlorobenzene = 70 mmHg .
Sol : The mixture have equal amount of liquids .
So N= 0.5
P(benzene) = 0.5 * 380 mmHg = 190 mmHg
P(chlorobenzene ) = 0.5 * 70 mmHg = 35 mmHg
P(total) = P(benzene) + P(chlorobenzene )
P(total) = 190 + 35 = 225 mmHg
When a mixture of benzene and acetic acid begins to boil , benzene is not
the only component to go into the gas phase . Some acetic acid molecules
will also go into the gas phase . However , since benzene is more volatile ,
more molecules of benzene will go into the gas phase. So if a 50 : 50 mixture
of benzene and acetic acid boils , the gas coming off will not be pure , but it
will also not be a 50 : 50 gas mixture . In figure (1) , the below curve shows
the boiling points for different mixtures of benzene and acetic acid the above
curve shows the composition of vapor at vapor at any given temperature.
- 29 -
Experimental 8:- ( Distillation )
Distillation is a physical method of assorting mixtures depending upon the
difference in the boiling point of the component substances. The working
principle of distillation is to heat a mixture at a specific temperature, collect
the hot vapors and condense to separate the component substance. In
simpler terms, a highly volatile compound is separated from a less-volatile or
non-volatile compound by using distillation. As per evidences, the principle of
distillation has been used since ancient times. Distillation is used for many
commercial
processes, such as production of gasoline, distilled water,
xylene, alcohol, paraffin, kerosene, and many other liquids.
Types of Distillation:There are several types of distillation depending on the procedure and the
instrument setup. Each of the distillation type is used for the purification of
compounds having different properties. Following are the common types of
distillation:
1- Simple Distillation :Simple distillation is practiced for a mixture in which the boiling point of
the components differ by at least 70°C. It is also followed for the mixtures
contaminated with nonvolatile particles and those that are nearly pure with
less than 10 percent contamination. Double distillation is the process of
repeating distillation on the collected liquid in order to enhance the purity of
the separated compounds.
- 30 -
2- Fractional Distillation :Those mixtures, in which the volatility of the components is nearly similar
or differs by 25°C (at 1 atmosphere pressure), cannot be separated by simple
distillation. In such cases, fractional distillation is used where by the
constituents are separated by a fractionating column. In the fractionating
column, the plates are arranged and the compound with the least boiling point
are collected at the top while those with higher boiling point are exist in the
bottom. A series of compounds are separated simultaneously one after
another. Fractional distillation is used for the alcohol purification and gasoline
purification in petroleum refining industries.
Azeotropic Distillation :. Owing to the intermolecular attractions between molecules in the mixture,
mixtures may have a higher or lower boiling point than either of their
components. A mixture of this kind is called an azeotrope. When the liquids in
the azeotrope evaporate, the vapor has the same composition as the mixture,
so azeotropes cannot be distilled using the techniques described above. They
can still be distilled, however, but only through one of several other methods.
3- Steam Distillation :Steam distillation is used for the purification of mixtures, in which the
components are temperature or heat sensitive; for example, organic
compounds. In the instrument setup, steam is introduced by heating water,
which allows the compounds to boil at a lower temperature. This way, the
temperature sensitive compounds are separated before decomposition. The
vapors are collected and condensed in the same way as other distillation
types. The resultant liquid consists of two phases, water and compound,
which is then purified by using simple distillation.
- 31 -
4- Vacuum Distillation :Vacuum distillation is a special method of separating compounds at
pressure lower than the standard atmospheric pressure. Under this condition,
the compounds boil below their normal boiling temperature. Hence, vacuum
distillation is best suited for separation of compounds with higher boiling
points (more than 200°C), which tend to decompose at their boiling
temperature. Vacuum distillation can be conducted without heating the
mixture, as usually followed in other distillation types. For the separation of
some aromatic compounds, vacuum distillation is used along with steam
distillation.
Procedure:
1. Make a table in your lab record book of Temperature, oC vs. Volume, mL.
2. Pour 30 mL of the compound into your 50 mL round bottom flask and add
2 boiling chips. Place the round bottom flask in a heating mantle and clamp
the round bottom flask. Set up the simple distillation apparatus shown in
Figure 1.
3. Start the water running slowly through the condenser and have the
instructor check the set up before starting to heat the flask. Make sure the
heating mantel is plugged into the Variac, not directly to the socket.
4. Regulate the heat control, starting at position 5-6 and decreasing to a lower
numerical value on the heat control, so that the rate of distillation is no
more than about 1 drop every 2 seconds. Collect the distillate in the
graduated cylinder. Record the temperature after every 2 mL of distillate.
- 32 -
( Figure 1 )
- 33 -
Experimental (9):-
( Thin layer chromatography (TLC) )
Thin layer chromatography (TLC) is a chromatography technique used
to identify range reaction ripening and to separate mixtures. Thin layer
chromatography is performed on a sheet of glass, plastic, or aluminum foil,
which is coated with a thin layer of adsorbent material, usually silica gel,
aluminium oxide, or cellulose. This layer of adsorbent is known as the
stationary phase.
Table 1: Types of Chromatography
Type
Gas
Stationary phase
chromatography Polar or non-polar
(GC)
Mobile phase
Helium gas
liquid
High Performance liquid
Solid
Liquid
Solid on glass or
Liquid
Chromatography
(HPLC)
Thin
Layer
Chromatography (TLC)
plastic plate
Thin-Layer Chromatography (TLC) is a simple and inexpensive
technique that is often used to judge the purity of a synthesized compound or
to indicate the extent of progress of a chemical reaction. In this technique, a
small quantity of a solution of the mixture to be analyzed is deposited as a
small spot on a TLC plate, which consists of a thin layer of silica gel (SiO2) or
alumina (Al2O3) coated on a glass or plastic sheet. The plate constitutes the
stationary phase. The sheet is then placed in a chamber containing a small
amount of solvent, which is the mobile phase. The solvent gradually moves
- 34 -
up the plate via capillary action, and it carries the deposited substances along
with it at different rates. The components then appear as a series of spots at
different locations up the plate. Substances can be identified from their socalled Rf values. The Rf value for a substance is the ratio of the distance that
the substance travels to the distance that the solvent travels up the plate.
Procedure :Preparing a spotting capillary, Glass capillaries used for spotting TLC
plates are commercially available. However, it is occasionally necessary to
make your own capillaries. To accomplish this, light a Bunsen burner and
adjust for a medium flame. Hold a melting point capillary in the flame until it
just begins to soften, then quickly pull the two ends of the capillary in opposite
directions. The central, soft part of the glass will elongate and thin down to a
capillary with very small diameter. Break the two pieces apart at the center of
the thin portion to obtain two TLC spotting capillaries. Marking the TLC Plate,
Obtain a silica gel TLC plate that is approximately 2 cm wide and 5 cm long.
Mark the TLC plate as follows using a pencil (pencil must be used rather than
pen because inks are moved by many developing solvents). First, lightly draw
a straight line parallel to the short dimension of the plate, about 1 cm from
one end of the plate. Don't gouge the silica gel or make a trough with the
pencil. This subdivided line will serve as a guide for placing the substance
spots, and as a point from which to measure Rf values.
- 35 -
Experimental (10):- (Elementary Analysis "Sodium Fusion)
The general rules to check sample:
1- Color: common colored compounds include nitro and nitroso
compounds (yellow), diketones (yellow), quinones (yellow to red), azo
compounds (yellow to red), and polyconjugated olefins and ketones
(yellow to red). Phenols and amines are often brown to dark-purble
because of traces of air oxidation products.
2- Odor : Some liquid and solid amines are recognizable by their fishy
odors; esters are often pleasantly fragrant. Alcohols, ketones, aromatic
hydrocarbons and aliphatic olefins have characteristic odors. On the
unpleasant side are thiols, isonitriles, and low MW carboxylic acids.
3- Make an ignition test: Heat a small sample on a spatula ; first hold the
sample near the side of a microburner to see if it melts normally and
then burns. Heat it in the flame. If a larg ashy residue is left after
ignition, the unknown is probably a metal salt. Aromatic compounds
often burn with a smoky flame.
This method for detection of nitrogen, sulfur, and halogen in organic
compounds depends upon the fact that fusion of substances containing these
elements with sodium yields NaCN, Na2S, and NaX(X=Cl, Br, I).
(C,H,O,N,S, halogen) + Na
NaCN + Na2S + Na.Hal. + NaOH
These products can, in turn, be readily identified . The method has the
advantage that the most usual elements other than C, H, and O present in
organic compound can all be detected following a single fusion, although the
presence of sulfur sometimes interferes with the test for nitrogen.
Unfortunately, even in the absence of sulfur the test for nitrogen is sometimes
unsatisfactory (nitro compounds in particular).It is essential to use an excess
of sodium, otherwise if sulphur and nitrogen are both present
- 36 -
Procedure for Lassaigne's test:
Place (4mm = 0.04gm) of freshly cut sodium in the dry tube have in
readiness about (0.5gm) of the compound (if solid) or about (3 drops) of the
compound (if a liquid) . Heat the tube steadily until sodium vapor with is dark
grey in color for two minutes and then allow it to coll.
Add about (0.5ml) of ethanol to decompose any un reaction sodium and then
add (5ml) of distilled water. Boil gently for a few minutes to remove the
ethanol. Filter and use the clear , colorless filtrate for the various test detailed
below , if the filtrate is dark colored repeat the entire fusion procedure. Or by
boil the dark filtrate with a little amount of charcoal and filter to produce the
colorless filtrate.
1-Detection of nitrogen:
Pour (2ml) of the filtered fusion solution in to a test tube containing
(0.1 –
0.2gm) of powdered ferrous ammonium to produce hexacyanoferrate(11).
Heat the mixture gently with shaking until it boils to produce some iron (111)
ions by the action of air. Then without cooling add just sufficient dilute
sulphuric acid to acidify the solution and produce the iron(111) hexacyano
ferrate (Prussian blue) .
6NaCN + Fe(NH4)2(SO4)2
Na2SO4 + (NH4)2SO4 + Na4[Fe(CN)6]
Complex green
3Na4[Fe(CN)6] + 2Fe2(SO4)3
Fe4[Fe(CN)6]4 + 6Na2SO4
(Prussian blue)
- 37 -
2-detection of sulphur:
This element may be tested for by either of the following two methods:
A-Acidify (1-2ml) of the fusion solution with dilute acetic acid add a few drops
of lead acetate solution . A black precipitate of lead sulphide indicates the
presence of sulphur .
Na2S + 2CH3COOH
H2S
+ 2CH3COONa
Pb(CH3COO)2 + H2S
PbS
+ 2CH3COOH
B- To (1-2ml) of the fusion solution add (2-3) drops of a freshly prepared
dilute solution (0.1%) of sodium nitroprusside [Na2Fe(CN)5NO.2H2O]. Purple
coloration indicates the present of sulphur.
Na2S + Na2[Fe(CN)5NO]
Na4[Fe(CN)5NOS]
3-Detection of halogens:
Acidify (2ml) of the fusion solution with a drops of dilute nitric acid (boil the
solution if the nitrogen and sulphur present) , add an excess of silver nitrate
solution. Precipitate silver halides to indicates the present of halogen. If the
precipitate is white , chlorine is present ; if it is pale yellow , bromine is
present ; if it is yellow , iodine is present.
Na2S + NaCN + 3HNO3
Na.Hal. + AgNO3
HCN
+ H2S
Ag.Hal. + NaNO3
- 38 -
+ 3NaNO3
Experimental (11) :- (preparation of acetylene)
Acetylene (systematic name: ethyne) is the chemical compound with
the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless
gas is widely used as a fuel and a chemical building block. It is unstable in
pure form and thus is usually handled as a solution. Pure acetylene is
odorless, but commercial grades usually have a marked odor due to
impurities. As an alkyne, acetylene is unsaturated because its two carbon
atoms are bonded together in a triple bond. The carbon-carbon triple bond
places all four atoms in the same straight line.
Preparation :
Today acetylene is mainly manufactured by the partial combustion of
methane or appears as a side product in the ethylene stream from cracking
of hydrocarbons. Its presence in ethylene is usually undesirable because of
its explosive character. Acetylene (and the aromatic fraction ) was the main
source of organic chemicals in the chemical industry. It was prepared by the
hydrolysis of calcium carbide, a reaction discovered by Friedrich Wöhler
in 1862 :
CaC2
+
2H2O → Ca(OH)2
calcium carbide
+ C2H2
hydrated lime
acetylene
procedure :
1. Put enough carbide chips to cover the bottom of the container.
Close the container tightly.
2. At the off position, add water about 10 minutes before you want to
light the lamp.
- 39 -
3. Turn to on position and wait. It takes about 10 minutes for the water
to start dripping into the lower compartment where the calcium
carbide is.
4. Acetylene thus produced is collected in a gas jar by the downward
displacement of water.
Detection of unsaturated bonds:
1- Reaction with Bromin water b :- add to the gas flask about of 0.2 ml
(four to five drops ) of Bromin water then close it with arubber.
2- Reaction with Iodene (alcoholic) :- add to another flask two drops of
Iodene then close it with arubber.
3- (Baeyer test) reaction with potasium permengenate :- solve (0.03gm) of
unknown in (2ml) of water or acetone in test tube . Then add to solution
drop by drop , from (1%) aqueous potassium permenganate solution
with strong move , the disappear of violet colour and appear of brown
ppt. of manganese dioxide refers to unsaturated bond duble or triple.
3 RC CR + 2MnO4 + 4H2O
3RC CR + 2MnO2 + 2OH
OH OH
- 40 -
Experimental 12 :-Lucas test (to distinguish between alcohols 1o, 2o, 3o )
There are a different between alcohols ( 1 o , 2o , 3o ) whene they are reacted with
hydrogen chloride in presence of zinc chloride and separated the alkyl chloride layer
that insoluble .
This is different in the rate of the reaction . Lucas test is prepared by mixing one
molecular weight of hydrochloric acid with one molecular weight of anhydrous zinc
chloride .Then mixing and keeping it in a lock flask.
procedure
Add (6ml) of lucas test to (1ml) of alcohol in test tube (clean and dry ) , then
stepper the tube arubber then mix the mixture , we observe that separation the
mixture to two layer but the rate of separation as below :a) 1o alcohol:- That under hexanol soluble in lucas test with colour the solution
, but the solution stay clear without separation layer . That uper than hexanol
do not soluble in solution .
b) 2o alcohol :- The solution is tyrbid by separation of drops of alkyl chloride
after 5min the apper layer are be separated .
c) 3oalcohol :- The two layer are be separated immediatly because of 3 o alkyl
chloride formation.
- 41 -
Experimental (13) :- (preparation of aspirin)
Aspirin, acetylsalicylic acid, was first synthesized in 1893 by Felix
Hofmann, a chemist for the German firm of Bayer. This compound had the
medicinal properties of salicylic acid, an extract of willow bark, without the
unpleasant taste or the high degree of irritation of the mucous membranes
lining the mouth, gullet, and stomach.
Aspirin is both an organic ester and an organic acid. It is used extensively
in medicine as a pain killer (analgesic) and as a fever-reducing drug
(antipyretic). When ingested, acetylsalicylic acid remains intact in the acidic
stomach, but in the basic medium of the upper intestinal tract, it hydrolyzes
forming the salicylate and acetate ions. However, its additional physiological
effects and biochemical reactions are still not thoroughly understood.
Aspirin (molar mass of 180.2 g/mol) is prepared by reacting salicylic acid
(molar mass of 138.1 g/mol) with acetic anhydride (molar mass of 102.1
g/mol).
- 42 -
Mech.
H2SO4
H + HSO 4
O
C
H 3C
O
O
O
C
O
C
+ H
H3C
CH3
C
O
CH3
H
O
O
C
+
OH
COOH
O
+
C
C
OH
H3C
H
O
O
C
CH3
CH3
COOH
CH3
O
O
+
Dehydration of
H
+
C
H3C
CH3
COOH
O
H2SO4
C
by HSO 4
OH
AsA
Aspirin
- 43 -
Procedure
1-Weigh out 2.0 g of salicylic acid. Place it in a 125-mL Erlenmeyer flask.
2-Add 5 mL of acetic anhydride. Swirl the flask to wet the salicylic acid
crystals. Add 5 drops of concentrated sulfuric acid, H2SO4 , to the mixture.
3-Gently heat the flask in a boiling water bath for (50 – 60)oC about 15
minutes with moving .
4-Remove the flask from the hot water bath and add 10 mL of ice water to
decompose any excess acetic anhydride. Chill the solution in an ice bath
until crystals of aspirin no longer form, stirring occasionally to decompose
residual acetic anhydride.
- 44 -
Experimental (14):- (Preparation of soap- hydrolysis of fats)
(( Soaponification of fats ))
All fats and oils that extracted from plants or enemals source are esters of
glycerol and long chain carboxylic acids. The common fat contain one or two
main long carboxylic acid , few of middile chain carboxylic acid and high
number of small structure acid. The most carboxylic acid that founded in fats
contain a pair numbers of carbon atoms in non branching chain as following :-
CH3(CH2)14CO2H
Palmitic acid
CH3(CH2)16CO2H
Stearic acid
CH3(CH2)7CH=CH(CH2)7CO2H
Dleic acid
We can prepared soap from fats and oils by hydrolysis in presence of
sodium hydroxide :
O
O
H 2C
O
C
O
R
HC
O
C
O
R'
H2C
O
C
R"
Fat
+ 3NaOH
H2 C
OH
HC
OH
H 2C
OH
Glycerol
+
Na
O
C
O
R
Na
O
C
O
R'
Na
O
C
R"
Sodium salt
(Soap)
We can use any fat or oil for this experiment but the best product of soap
prepared from solid fat (cacoa oil , margrine , cooking fat ….. etc)
- 45 -
Procedure :
1- Put a mixture of (15gm) of fat or oil and (15ml) of (2.5M) of NaOH
solution and (15ml) of ethanol in flask.
2- Heating the mixture above water bath for (30 min) with moving until
disappear ethanol odor and become the mixture limy high degree .
3- Stop the heating and cool the flask .
4- Add with moving by slowly addition a saturated solution of NaCl .
5- Filter the soap then wash it by small amount of disttuled water.
6- Transfer small amount of the soap to watch glass and let it to dry.
Tests:
1- Test the foam of product by hands with water and the solubility of it .
2- Acidify (5gm) of soap solution by dil.H2SO4 , then filter the separated
organic comp. (keep the super note), then wash it with water then test
the solubility in water , compare it with (1) , test the reaction of
separated organic comp. with sodium hydroxide solution.
- 46 -