TASK 2
PREPARATION OF ASPIRIN
Synthesis of Aspirin
We followed a set of instructions on the sheet given to us in order to carry
make a pure sample of aspirin and calculate it’s % purity, % yield and atom
economy. When preparing aspirin, we mixed 2.0 g of 2-hydroxybenzoic acid
(salicylic acid) with 4 cm3 of Ethanoic anhydride then added 5 drops of
concentrated sulphuric acid. After the crystals appeared and later formed crystal
mush, we diluted it in ethanoic acid and dried it in ice. We then filtered off the
crystals and put the filtrate in boiling water to dissolve. We reserved some
crystals for further testing. We recrystallized the rest of the crystals and filtered it
after we let it cool. It is important to recrystallize the aspirin because the reaction
may contain by-products and they need to be removed to obtain pure aspirin. If
these instructions were followed properly and all possible errors were avoided,
we would be able to come out with 100% pure aspirin.
ESTIMITING PURITY
Iron chloride test
This is one of the following methods we used to test purity of aspirin. By
following the instructions on the sheet, we added 2 cm3 of distilled water to 4
different test tubes that we labelled. To one tube we added one crystal of the
aspirin we made before recrystallization and shook it. Then to another test tube,
we added one crystal of the crystalized aspirin we made and shook it. To another
test tube, we added one crystal of 2-hydrobenzoic acid and shook it. Then to the
last test tube, we added one crystal of known pure aspirin and shook it. Lastly, to
each test tube, we added 2 drops of neutral iron (III) chloride solution and shook
it. If the product is pure aspirin, it should turn yellow and the ones with impurities
would be dark purple.
Melting point determination
The melting point of aspirin was taken as another means to identify, and test
the purity of the product. We set up the apparatus as demonstrated by our
teacher and we heat the oil at a rate of 1 to 2 degrees per minute as we
approached the melting range of the sample. We used a capillary tube with one
sealed end and filled it up with the sample then melted the under end. After that,
we placed the tube inside the melting point apparatus and increased the
temperature slowly while recording the temperature. To avoid errors, didn’t heat
the oil for too long. The melting point of aspirin was not consistent with the
literature value which is 135 degrees Celsius while ours was 135 degrees Celsius.
This shows that the synthesised aspirin was not pure.
Thin Layer Chromatography (TLC)
Chromatography is a physical method used to separate mixtures of coloured
substances. We set up the apparatus as demonstrated by our teacher and
followed the following instructions to analyse and check the purity of aspirin
using TLC. Using a pencil, we drew a line across the plate about 1 cm from the
bottom and top. Then we marked 4 equally spaced points on the line drawn at
the bottom of the plate and placed a small drop of each of the different samples
PREPARATION OF ASPIRIN
Synthesis of Aspirin
We followed a set of instructions on the sheet given to us in order to carry
make a pure sample of aspirin and calculate it’s % purity, % yield and atom
economy. When preparing aspirin, we mixed 2.0 g of 2-hydroxybenzoic acid
(salicylic acid) with 4 cm3 of Ethanoic anhydride then added 5 drops of
concentrated sulphuric acid. After the crystals appeared and later formed crystal
mush, we diluted it in ethanoic acid and dried it in ice. We then filtered off the
crystals and put the filtrate in boiling water to dissolve. We reserved some
crystals for further testing. We recrystallized the rest of the crystals and filtered it
after we let it cool. It is important to recrystallize the aspirin because the reaction
may contain by-products and they need to be removed to obtain pure aspirin. If
these instructions were followed properly and all possible errors were avoided,
we would be able to come out with 100% pure aspirin.
ESTIMITING PURITY
Iron chloride test
This is one of the following methods we used to test purity of aspirin. By
following the instructions on the sheet, we added 2 cm3 of distilled water to 4
different test tubes that we labelled. To one tube we added one crystal of the
aspirin we made before recrystallization and shook it. Then to another test tube,
we added one crystal of the crystalized aspirin we made and shook it. To another
test tube, we added one crystal of 2-hydrobenzoic acid and shook it. Then to the
last test tube, we added one crystal of known pure aspirin and shook it. Lastly, to
each test tube, we added 2 drops of neutral iron (III) chloride solution and shook
it. If the product is pure aspirin, it should turn yellow and the ones with impurities
would be dark purple.
Melting point determination
The melting point of aspirin was taken as another means to identify, and test
the purity of the product. We set up the apparatus as demonstrated by our
teacher and we heat the oil at a rate of 1 to 2 degrees per minute as we
approached the melting range of the sample. We used a capillary tube with one
sealed end and filled it up with the sample then melted the under end. After that,
we placed the tube inside the melting point apparatus and increased the
temperature slowly while recording the temperature. To avoid errors, didn’t heat
the oil for too long. The melting point of aspirin was not consistent with the
literature value which is 135 degrees Celsius while ours was 135 degrees Celsius.
This shows that the synthesised aspirin was not pure.
Thin Layer Chromatography (TLC)
Chromatography is a physical method used to separate mixtures of coloured
substances. We set up the apparatus as demonstrated by our teacher and
followed the following instructions to analyse and check the purity of aspirin
using TLC. Using a pencil, we drew a line across the plate about 1 cm from the
bottom and top. Then we marked 4 equally spaced points on the line drawn at
the bottom of the plate and placed a small drop of each of the different samples
