CONTENTS
CONTENTS
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PAGE
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Abstract
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2
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Introduction
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3
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Literature
review
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5
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Objectives
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7
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Methodology
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8
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Results
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10
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Discussion
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11
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Conclusion
and recommendation
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15
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Reference
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16
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Appendix
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Abstract
This is an experiment to study the
effectiveness of two different types of liquid extraction, namely single
extraction and multiple extractions. The solute, crystal violet was to be
extracted from its aqueous solution.
Part A of the experiment involved
simple extraction, which is single extraction using a fixed volume of organic
solvent, 10ml dichloromethane. The extraction process was carried out using a
seperatory funnel and the aqueous crystal violet left from the extraction was
transferred into a test tube for later comparison with Part B of the
experiment. In Part B of the experiment, similar procedure was carried out, but
instead of using 10ml dichloromethane all in once, the extraction was done two
times, with 5ml dichloromethane each. The aqueous crystal violet collected from
this part of the experiment was compared with that in Part A of the experiment.
The colour intensity of the solutions
gave an idea of how effective the extraction was. This is because the more
crystal violet was present in the aqueous solution, the more purple the
solution was. Higher amount of crystal violet in the aqueous solution indicated
a less effective extraction, since less crystal violet was drawn into the
organic solvent. Therefore, the aqueous solvent with a higher intensity of
purple colour was obtained from a less effective extraction.
In this experiment, the organic
solvent, dichloromethane must be handled with care and goggles must be worn,
because excess exposure to the substance causes cancer. During the procedure of
extraction, the seperatory funnel must be opened after shaking the contents in
it because vigorous shaking of the contents produces vapour. The high pressure
inside the funnel might explode the apparatus and cause injuries if it wasn’t
released.
Introduction
There are two main applications of extraction
in the organic laboratory :
(1) The separation and isolation of substances
from mixtures of solids; typically those that occur in nature and
(2) The selective isolation of substances from
solutions of mixtures that arise in synthetic chemistry.
Extraction
of solid
Examples of extraction of solid mixtures are
the extraction of alkaloids from leaves and bark, flavouring extracts from
seeds, perfume essence from flowers, and sugar from sugar cane. Solvents
commonly used for this purpose are ether, dichloromethane, chloroform, acetone,
various alcohols, and water. Brewing coffee is an example of liquid-solid
extraction. The lower molecular weight polar molecules such as caffeine
dissolve in the hot water and are removed from the high molecular weight
water-insoluble cellulose, protein, and lipid materials. Over 200 compounds,
some in only trace quantities, are extracted from the solid into a cup of
coffee or tea. Decaffeinated coffee is also an excellent example of
solid/liquid extraction. Coffee manufacturers extract the caffeine from the
coffee to provide modern society with a decaffeinated version of an ancient
drink.
In the laboratory, a common form of apparatus
for continuous extraction of solids by means of volatile solvents is the
Soxhlet Extractor, as shown in the diagram below.
Vapour from the boiling extraction solvent in
the boiling flask rise through the vertical tube at the left into the condenser
at the top. The liquid condense drips into the filter paper in the thimble,
which contains the solid sample to be extracted. The extract seeps through the
pores of the thimble and eventually fills the siphon arm at the left, where it
can flow back down into the boiling flask. With the apparatus shown, the
siphoning action is intermittent. No liquid will flow through the siphon until
the liquid level in the thimble reaches the top of the siphon arm. At that
point almost all of the liquid in the siphon and the thimble drain out and the
cycle of filling and draining starts again.
Extraction of
liquids
Liquid extraction is also known as solvent
extraction or partition. It is basically the extraction of a solute from a
liquid phase to another liquid phase, where both the liquids (solvents) are
miscible in each other. The solvents involved are usually water and an organic
solvent, since the solute to be extracted is usually organic substance. Liquid
extraction is also possible in non-aqueous phase, where electrodes are involved
in the extraction of molten metal in contact with molten salts. In most cases,
the metal is the substance which is to be extracted. Liquid extraction is
applied in nuclear reprocessing, ore processing, the production of fine organic
compounds, the processing of perfumes, the production of vegetable oils and
biodiesel, and other industries.
In extraction of liquids, there is a constant
coefficient called distribution ratio. This is the ratio of concentration of
the solute in the organic phase divided by its concentration in the aqueous
phase. The distribution ratio, also known as the partition coefficient, only
holds under the conditions where the two solutions (organic and aqueous
solvent) are reasonably dilute, the solute does not react, associate or
dissociate in the solvents, and the temperature must be kept constant. In such
conditions, distribution ratio can be a measure of how effective the extraction
of a species is.
Extraction of liquids can be done by
a single extraction or multiple extractions where organic solvent of a same
volume is added separately to repeat the process for times. This is the two
kinds of liquid extraction being compared in this experiment.
Literature Review
Liquid–liquid
extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their
relative solubility in two different immiscible liquids, usually water and an organic solvent. Liquid-liquid
extractions using a separatory funnel are essentially the only kind of extraction
performed in the organic teaching labs. The "liquid-liquid" phrase
means that two liquids are mixed in the extraction procedure. The liquids must
be immiscible: this means that they will form two layers when mixed together,
like oil and vinegar do in dressing. Some compounds are more soluble in the
organic layer (the "oil") and some compounds are more soluble in the
aqueous layer (the "vinegar").It is an extraction of a substance from one liquid phase into another liquid phase. This type of
process is commonly performed after a chemical reaction as part of the work-up.
The term partitioning is commonly used to refer to the
underlying chemical and physical processes involved in liquid–liquid extraction but may be fully synonymous. The term solvent extraction can also refer to the separation of a
substance from a mixture by preferentially dissolving that substance in a
suitable solvent. In that case, a soluble compound is separated from an
insoluble compound or a complex matrix.
Extraction with solvents is divided into two
parts, which are single extraction and multiple extractions. Single extraction
means the combination of an organic solvent and water to form a bilayer (such
as ether and water) in a vessel (for example a separatory funnel) and then
shake to thoroughly mix the two solvents. The seperatory funnel is then allowed
to stand which causes the mixture to separate into two layers which can be
removed.
Multiple extractions is, after the two layers
are separated, more water is added to the org layer or more organic solvent is
added to the aqueous layer and the process is repeated. Once the two layers are
separate, the similar layers (e.g. the two organic layers) are combined.
Liquid-liquid extraction involving non-aqueous
systems is related to a mercury electrode where a metal can be reduced, the
metal will often then dissolve in the mercury to form an amalgam that modifies
its electrochemistry greatly. For example, it is possible for sodium cations to
be reduced at a mercury cathode to form sodium amalgam, while at an inert
electrode (such as platinum) the sodium cations are not reduced. Instead, water
is reduced to hydrogen. A detergent or fine solid can be used to stabilize an
emulsion, or third phase.
Liquid extraction, single and multiple alike,
can be measured its effectiveness by the calculation involving distribution
ratio or partition coefficient. Since the distribution ratio changes with
temperature, the distribution ratio can be a function of temperature, the
concentration of chemical species in the system, and a large number of other
parameters.
Considering
about the factors affecting distribution ratio, the factors can actually be
manipulated to affect the yield and therefore the selectivity of an extraction.
Depending on the nature of the extraction process, the temperature, pH and
residence time could have an effect on the yield and selectivity. Most extractions take place at atmospheric
pressure unless governed by vapour pressure considerations, because pressure
has negligible effect on the yield and selectivity.
Temperature can also be used as a variable to
alter selectivity. Elevated temperatures
are sometimes used in order to keep viscosity low and thereby minimizing
mass-transfer resistance. Other
parameters to be considered are selectivity, mutual solubility, and
precipitation of solids and vapour pressure.
The pH becomes significant in metal and
bio-extractions. In bio-extractions
(e.g., Penicillin) and some agrochemicals, pH is maintained to improve
distribution coefficient and minimize degradation of product. Sometimes, the
solvent itself may participate in undesirable reactions under certain pH
conditions (e.g., ethyl acetate may undergo hydrolysis in presence of mineral
acids to acetic acid and ethanol). This unable the extraction to be predicted
and done properly since one of the conditions for having a constant
distribution coefficient is that the solvents do not undergo any chemical
reactions.
Residence time is an important parameter in
reactive extraction processes (e.g., metals separations, formaldehyde
extraction from aqueous streams) and in processes involving short-life
components (e.g., antibiotics & vitamins).
Objective
To demonstrate the effectiveness of a single
extraction with a fixed volume of solvent compared to multiple extraction, each
with one half of the fixed volume.
In this
experiment, crystal violet is to be extracted from its aqueous solution using
organic solvent, dichloromethane. This experiment aims to compare the amount of
crystal violet extracted by 10ml dichloromethane in single extraction, with
multiple extraction using 5ml dichloromethane for two times in a multiple
extractions.
Methodology
Equipment and apparatus
20ml
crystal violet, 125ml separatory funnel, 20ml dichloromethane, rubber stopper,
Erlenmeyer flask, 25ml beakers, test tubes.
Procedures
Note: the content of the test tubes is
disposed of as directed by the instructor as each procedure is finished. The
glassware is washed thoroughly with soap and water, and then all the equipment
and chemicals are returned to the designated areas.
A. Simple extraction
1. 10ml of the stock aqueous solution of
crystal violet is placed in a 1225ml separatory funnel and extracted with 10ml
dichloromethane in the following manner.
2. The separatory funnel is stoppered,
shaken gently, and turned upside down.
3. While the separatory funnel is in
this position, the stopcock is opened to release the internal pressure then
closed again. theseparatory funnel is shaken vigorously, and the internal
pressure is released again.
4. This procedure is repeated four or
five times, then the separatory funnel is supported upright and let to stand
undisturbed.
5. When the liquids have separated
completely, the lower dichloromethane layer is drawn into an Erlenmeyer flask.
6. A portion of the remaining aqueous
layer is transferred to a test tube and set aside for later comparison.
Caution:
Do
not point the stem of funnel at anyone when the pressure is released. Any
liquid in the stem may be ejected forcefully.
Prolonged
exposure to high concentrations of dichloromethane vapors may induce cancer. As
with all organic solcents, it should be used in a well-ventilated area.
B. Multiple extraction
1. The separatory funnel is cleaned well
with water and a second 10ml porton of the stock solution of crystal violet is
placed in it.
2. The solution with 5ml of
dichlorimethane is extracted as described in Part A. the dichloromethane layer
is drawn off into the Erlenmeyer flask and the remaining aqueous layer is
extracted with a second, fresh 5ml portion of dichloromethane.
3. The dichloromethane is drawn off into
Erlenmeyer flask and a portion of the aqueous layer is transferred into a test
tube of the same size used in Part A.
4. Both tubes are filled to the same
height. The effectiveness of extraction by the two different procedures is
compared by noting the intensity of colour remaining in the aqueous layer.
Results
Type of extraction
|
Intensity of purple colour
in aqueous layer
|
Dimple extraction (Part A)
|
Higher intensity
|
Multiple extraction (Part
B)
|
Lower intensity
|
Discussion
Crystal violet is an organic
substance which gives a purple colour to its solution. It has a structure as
shown below. In aqueous solution, OH- ion bonds itself to the
auxochrome group.
The crystal violet dissolves in
dichloromethane according to the like dissolves like theory, where organic
solutes dissolve in organic solvents. This explains why dichloromethane is used
as a solvent to extract crystal violet from its aqueous solution.
From the extraction done in this
experiment, the results show that multiple extraction is more effective than
single extraction. In Part A of the experiment, the intensity of purple colour
of the aqueous crystal violet after the extraction is higher than that in Part
B of the experiment. This means that less crystal violet was extracted from its
aqueous solution in Part A. Therefore, the extraction in Part A, which is
single extraction, is less effective than the extraction in Part B. A single
extraction with a fixed volume of solvent is less effective compared to two
extractions, each with one half of the fixed volume.
This
can be explained with an example involving distribution ratio:
Given that the distribution ratio of
X between ether and water is 40.0 at room temperature. When 1.0 dm3
of an aqueous solution containing 5.0g of X is extracted,
Case 1: in single extraction with 50cm3 of ether,
40.0
= 
Let
the mass of X extracted into the ether layer = m g
Mass
of X in water = (5.0 - m) g
=
40.0
m=3.33
g
Case 2: in multiple extraction with two successive 25cm3
portions of ether,
First extraction
Let
the mass of X extracted into ether = m1 g
Mass
of X in water = (5.0 – m1) g
40.0
= 
m1
= 2.5 g
Second
extraction
Mass
of X present in water after first extraction =5.0 g – 2.5 g = 2.5 g
Let
mass of X extracted into ether in second extraction = m2 g
Mass
of X in the water = (2.5 – m2) g
40.0
= 
m2
= 1.25 g
Total
mass of X extracted into the ether layer = (m1 + m2) g
=
(2.5 + 1.25) g
=
3.75 g
From
this example, it is clearly shown that the total mass of X extracted by ether
in two smaller portions is larger than the total mass extracted by one large
portion.
This
shows that multiple extraction is more efficient than single extraction.
1.
Write the chemical equations for any
reactions involved.
In the aqueous solution,
+
(CH3)2 N
C C N (CH3)2 + OH-
(CH3)2N |
(CH3)2
N OH
C C N (CH3)2 
(CH3)2N
When crystal violet is extracted from
its aqueous solution into the organic solvent, the equation below takes place.
+(CH3)2
N
C C N (CH3)2 (aq)(CH3)2N |
+(CH3)2
N
C C N (CH3)2 (org)(CH3)2N
2. What properties do you look for in a good solvent for extraction?
The two solvents must be
miscible in one another. Since most of the time water is one of the solvent, we
can say that the solvent used for extraction must be miscible with water.
The solvent should be
polar and can form hydrogen bonds for a good recovery of analyses in the
organic phase.
Usually, a solute with low
boiling point and evaporates easily is more likely to be chosen in an
extraction. This is because after extracting the solute, the solvent has to be
removed to obtain the solvent. With such properties, the solute can be obtained
easily after extraction.
Conclusion
&Recommendations
Conclusion
Multiple extraction is more effective than single extraction. Based on the
results of this experiment, extracting a solute with two extraction, each with
one half of the fixed volume of the solvent, is more effective than the single
extraction with the fixed volume of solvent. In other words, multiple
extraction can extract more solute from the original solution, and dissolves
the solute in the organic solvent used.
Recommendation
After shaking the separatory funnel
containing the two solutions vigorously, the stopcock should be opened to
release the internal pressure because there is vapour produced during the
process of shaking. The stem of funnel
should not be pointed at anyone when the pressure is released. Any liquid in
the stem may be ejected forcefully due to the high pressure inside the funnel.
Goggles and other suitable safety
costumes should be worn while handling the chemicals. The handling of chemicals
should be done fast and effectively in a chemical chamber, and the laboratory
must be well-ventilated. This is because exposure to high concentrations of
dichloromethane vapour may induce cancer. All the other organic solvents should
be used in a well-ventilated area as well.
After finishing the procedures, the
content of the test tubes must be disposed of properly. The apparatus should be
cleaned well with water after Part A of the experiment to prevent contamination
of the apparatus during the second part of the experiment, which might cause
inaccurate results.
Reference
·
Experimental
Organic Chemistry A small-Scale Approach by Charles F. Wilcox, Jr and Mary F.
Wilcox 2nd Edition.
·
Introduction to
Organic Laboratory Techniques : A small Scale Approach by Donald L.Pavia –
Science 2004
·
J. M. Sánchez, M.
Hidalgo, M. Valiente and V. Salvadó, Solvent Extraction and Ion Exchange, 1999
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