The Use of Recrystallization to Isolate Acetylsalicylic Acid from
The purpose of this
experiment was to isolate acetylsalicylic acid from Aspirin tablets. This was
done using recrystallization. The percent recovery, Nuclear Magnetic Resonance
spectrum, and melting point was then determined.
this experiment, the process of recrystallization was used to achieve the goal
of separating the acetylsalicylic acid from the aspirin tablets. The crushed
tablets were boiled in a sample of ethanol followed by two separate filtration
methods. The first filtration to occur was a gravity filtration which separated
the solid particles that did not dissolve in the compound. The compound was
placed in an ice bath afterwards which was followed with the second filtration,
a vacuum filtration. This second filtration was used to dry the solid crystals
and remove all liquid from them. Letting the formed crystals dry in the vacuum
filter allowed for an accurate measurement of the melting point. It also
provided an accurate weight of the crystals since that extra liquid would have
added to the final, and inaccurate, weight.
Salicylic Acetoc Acetylsalicylic
Acid Anhydride Acid
Results and Discussion:
This experiment utilized the process of recrystallization to
isolate the desired product. The desired product was acetylsalicylic acid. The
process of recrystallization included crushing Aspirin tablets, boiling the
crushed tablets in a solution of ethanol, filtering out the impurities through
gravity filtration, and finally, drying the isolated crystals using vacuum
filtration. Every part of the process that was expected, such as the presence
of solid impurities during the boiling process and the formation of crystals in
the ice bath, occurred in the manner in which it was expected to occur.
Initial mass of Aspirin
Color of Aspirin Tablets
Description of Crystals
Formed in Ice Bath
White and fine
Description of Crystals
after Vacuum Filtration
White and seemingly dry
Final Weight of Crystals
Melting Point Range
95?C – 103?C
initial weight of the five tablets was 1.8739g. These were then crushed and
boiled in about 7mL of ethanol and then the impurities were filtered out of the
solution via gravity filtration. The solution was then placed in an ice bath
allowing the crystals to form (recrystallization) which were then dried via
vacuum filtration. After being dried, the crystals were weighed and then a
sample was taken and melted in order to determine the melting point range.
The final weight of the
isolated product was 0.4344g. Using these numbers, a percent recovery of 23.18%
was calculated by dividing the final weight by the initial and multiplying that
by 100. This means that almost a quarter of the initial product in terms of
weight remained at the end of the experiment. The melting point range was also
determined. The range was between 95?C and 103?C. This is a smaller range which
means that the substance contained less impurities. If the range was very
broad, it would mean that it contained more impurities which hinder an accurate
measurement. While the melting range shows less contamination of impurities,
the high percent recovery shows otherwise. There might have been significant
amount of impurities still left in the final product or a significant amount of
liquid that remained from the drying process which caused such a large percent
experiment is viewed as a success. The percent yield and melting point range
were calculated properly, being 23.18% and 95?C – 103?C, respectfully. There
may have been some error in terms of impurities being present in the final
product or it not being dry enough from the vacuum filtration, however, the
overall experiment achieved what it was designed to ultimately accomplish.
Would recrystallization work if you had more impurity than
product and both were soluble in the recrystallization solvent at its boiling
point and insoluble at room temperature?
Recrystallization would not work because separation of the
product and impurities would be impossible. As the product would crystallize,
so would the impurities and vice versa. One has to remain soluble and the other
insoluble at a given temperature.
Why is it important to perform a hot gravity filtration of
the impurities instead of a gravity filtration at a lower temperature?
It was important to perform a gravity filtration of
impurities at a hot temperature rather than cold because at high temperatures
the aspirin remains dissolved and would pass through the filter whereas at a
lower temperature, it would crystallize and get trapped in the filter with the
other impurities. This concept is shown in the step where the solution was put
in an ice bath. Because of the lower temperature, every component crystallizes
almost instantly and does not stay dissolved.
If all the physical characteristics of your isolated material
matched that of ASA, except the melting point range was very broad and lower
than the reported value, what could be the cause?
If all the physical characteristics of the isolated material
matched that of ASA except in terms of the melting point range, then it could
be the cause of a couple issues. The first cause could be that the isolated
material contained a lot of impurities in addition to the ASA. Another cause
could be that the isolated material was not completely dry after vacuum
filtration. Either error would cause the same issue.