Essay
Unit 4 - D2 evaluate the accuracy of the methods used to estimate the purity of the samples
- Institution
- PEARSON (PEARSON)
This is my D2 task for my distinction graded unit 4 assignment
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Unit 4 – scientific practical techniquesD2 – Evaluate the accuracy of the methods used to estimate the purity of the samples
Accuracy in estimating the purity of our aspirin samples is key as it allows us to be certain of how
close our aspirin sample is to the pure aspirin sample. However, any experiment or test has
improvements due to accuracy not 100%.
In the melting point of aspirin one thing that reduced our accuracy, is the fact the machine
did not cool down before our samples were placed into the slots. This meant that the machine was
already hot and so when our samples were placed in, it could have taken some time before it
became clear. But if the machine was cool when our samples were placed in then there wouldn’t
have been any time needed to adjust to the heat due to the fact the temperature would have slowly
risen up and our aspirin could have turned clear a lot sooner and so at a lower temperature.
Another point is that while our aspirin samples were in the machine, we didn’t have our eyes
constantly watching for the change from crystals to clear, a few seconds were taken to look away
and when eyes were concentrated back onto the sample a clear sample was visible. These few
seconds could have been the difference of one degree meaning our sample could have been lower in
temperature and therefore less pure overall.
However, one thing that ensured the accuracy in the estimation was that a sufficient amount of our
sample was put into the capillary tube. This allowed the ruling out of a quick change of colour if
there was only a small amount of aspirin in the tubes and therefore incorrect results. And so, enough
of the sample allowed for accurate results to be collected .
In thin layer chromatography, one thing that reduced the accuracy was that under the UV
light the distances were not measured. This was due to loss of time and unsure at the time of exactly
how to figure out the purity of our sample compared to the shop bought aspirin sample. And so, a
picture was used and measured up to the size of the picture in real life and measurements were
taken from the phone. This is in no way accurate as the picture was taken at an angle and a few
millimetres could have easily been missed off for the calculations. This means there could have been
a bigger or smaller difference between the two samples.
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