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Team 10

Practice report
Practice 3 'Recrystallization'
Introduction

Crystallization is the most commonly used method for the purification of solids. In
In general, crystallization is based on the difference in solubility of a compound in
a certain solvent in cold and hot. The method consists of dissolving the
composed in the minimum amount of the solvent in hot, filter to remove all
the insoluble impurities (if there are any), and let cool so that the
Crystallization. Finally, the crystals are separated by filtration and left to dry.
Crystallization is an equilibrium process, and therefore it must be slow, so that the
strange particles are excluded from the crystal that forms and the final result is obtained
pure compound.” (Freeman, 2002)

Crystallization (or recrystallization) is a process in which a

substance to saturated solution at boiling temperature, it is filtered to obtain the
substance and is dried to obtain crystals of the substance with a higher purity
than what it had in its initial state.

Objectives

Know and apply the recrystallization technique to purify compounds

solid organics.
Apply the concepts of structure and polarity of compounds.
Select solvents for a recrystallization process.

Results

Results of experimental procedure 1: Solubility tests.

*Symbolism

Insoluble in cold
Soluble in hot, P= precipitates when cooling the solution.

Table 1 - Solubility in Acetanilide

Acetanilide
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H2O SC, P

Ethanol SF

Acetone SF

Ethyl acetate SF

Hexane SF

Table 2 - Solubility in Salicylic Acid

Salicylic acid

H2O SC, P

Ethanol SF

Acetone SF

Ethyl acetate SF

Hexane SF

Table 3 - Solubility in Dibenzalacetone

Dibenzalacetone
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H2O Insoluble

Ethanol SC, P

Acetone SC, P

Ethyl acetate SF

Hexane SC

Results of experimental procedure 2: Recrystallization of a compound

crude organic solid.

Raw acetanilide: 1g

Melting point: 113°C

Weight of the crystals: 0.85g

I calculate the recovery calculation

% =( ) * 100

0.85g
% = )( * 100
1g

% = 85%

Analysis of results

For the experimental part 1: Solubility tests.

As observed in tables 1, 2, and 3; not all compounds dissociate in the

presence of certain reagents, nor in the same way since some may
totally dissociate, partially or in some cases, like in the case of the
dibenzylacetone with water, null. This added to factors such as polarity.
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of the compounds involved and the temperature, as solubility also varies

regarding her.

For the experimental part 2: Recrystallization of a crude organic compound.

The yield of the process for obtaining pure acetanilide was 85%, therefore
there was a 15% loss of reagent. This being a relatively low percentage
regarding impurities contained in the reagent.

Discussion

According to what was done in this practice, we can notice certain situations that
they can affect the results of a recrystallization process. One of them is the
selection of the solvent, which as seen in the processes, must be able to dissolve the
dissolve at high temperature, since if it dissolves only in cold, this can affect
the process, this based on nucleation, which is the moment when it precipitates the
first crystal, this happens when the dissolved solution is suddenly cooled to temperature
high and depending on the speed of crystallization, larger crystals will be obtained
or small ones that ideally would be small, if it dissolves to
low temperature and there is no sudden temperature change it does not crystallize
shape waiting. Another factor that can affect our process is the dissolution itself,
since if the concentration differs from that of a saturated solution, this causes
that the crystallization does not occur correctly and very coarse crystals are formed.

The use of the concepts of solubility and polarity must be recognized, which are
of utmost importance for the process, as they determine whether it is possible to subject
the substance to a recrystallization process, polar components dissolve in
polar media and non-polar components in non-polar media.

The melting point determines the purity of the crystals, as well as whether they are crystalline and

even the size.

Conclusion

The recrystallization process is one of the most basic and important in the industry.
since it allows us to obtain solid compounds with a high degree of purity for
drugs or products that need the active ingredients of the substances, are
it concludes that in a recrystallization there are several factors that influence the obtaining
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effectively of the expected products, the hot solution will determine the
crystal formation given that when cooling the molecules start to attract each other
they are packing into crystals, also the speed at which the process occurs
it will affect performance, the faster the nucleation process is carried out
they will obtain small crystalline crystals, which are characteristic of having greater purity.

Bibliography

Activated Carbon: Clinical Toxicology

Unable to access the URL for content to translate.

●Pasto, D; Johnson, C. (2003). Determination of organic structures.

Barcelona: REVERTÉ.

W.H. Freeman and Company. (2002). Study guide and solutions manual, (4th
Ed.)

Questionnaire

1. Explain what activated charcoal is used for.

Activated charcoal has various applications:

In medicine, it is used as a detoxifier for poisons and toxins.

originating from fungi, toxic plants, organophosphate insecticides,
etcetera; that can circulate enterohepatically (secretion process
and reabsorption of bile salts).

In the industrial field, it is used as a purifier of liquid solvents,

among them water, where it traps impurities from industrial waste,
pesticides, among others.

In deodorization and air purification: activated carbon is used in

air recirculation systems, drainage vents, and treatment plants
of water.

In the sugar refinery field, coal is used to prevent the

sugar undergoes the fermentation process and decomposes.
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It is used in the decolorization of essential oils and some liquids (such as

alcoholic beverages) thanks to electrostatic reactions.

2. Indicate why it is important to minimize evaporation during filtration

from a hot solution.

It is important, since by reducing evaporation, the formation of crystals is avoided in

the filtering funnel.

3. In the purification of a solid by recrystallization in a solvent, explain if it is

It is advisable to cool the solution quickly or slowly.

It is advisable for the solution to be cooled quickly, as doing so

this way we can get small crystals. If we do it slowly what
it will occur that large crystals will form (the larger the size of the crystal,
the greater the amount of impurities present).

4. If the melting points determined for the purified compounds do not match
with the reported ones. Indicate what interpretation would be given to this fact and propose what

the procedure would follow based on your interpretation.

It may be due to the presence of impurities in the compounds, these impurities

causing the original melting point to decrease. In these cases, it is suggested to carry out
the crystallization process once again, making sure this time that the compound does not
contaminate.

5. Explain why the solubility of a compound in a solvent increases when

increase the temperature.

This happens because interactions that were already established are broken due to
from the kinetic energy of the molecules, then the solvent is allowed to
combine with the solute and create new compounds.

6. Indicate what conditions determine that a substance (solute) dissolves in another (solvent).

A conditional factor is the intermolecular interactions between the compounds.

(solute and solvent), these interactions must be favorable. Another factor is the
solubility of substances since not all substances dissolve equally
measured in the same solvent. A third factor would be temperature (in solids and
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liquids), as the temperature increases, the kinetic energy increases, which causes
greater interaction among its molecules. And finally the pressure, it intervenes
when it comes to a gas) proportionally to the solubility.