Student example report
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Cholesterol (0.5g), acetic acid (5mL), and acetic anhydride (1mL) were combined in a round-bottomed flask, and heated over a steam bath for 5 minutes with a condensor connected vertically to the flask. The solution was then cooled, and water (20mL) added.
Stephen comments on the way to present quantities and volumes
...Boiling chips were then added to the filtrate, which contained ether and cholesteryl acetate, and boiled over a steam bath to remove the ether. ...
Stephen advises students about describing equipment (14sec):
Four fractions of 10mL each were collected, and tested for purity using TLF plates, against a standard cholesterol solution.
Stephen comments on the way to present the yield (9sec) and explains about showing the calculation of percentage yield (17sec):
1. Rf (cholesterol) = 0.5cm/4cm = 0.125
Rf (cholesterol acetate) = 3.4cm/4cm = 0.85
The size, shape, and most importantly the polarity of a molecule/compound affects the interaction that it has with silica.
During the column chromatography, the more polar cholesterol was adhering better to the silica than the cholesteryl acetate, and so it was running down the column at a much slower rate. Similarly, the silica plate is .....
Stephen suggests that students comment on what they've found rather than just recording it (32s):
Ahn talks about how her writing has improved (1m 2s):
Stephen comments on the way to present a yield (9s):
Stephen advises students about describing equipment (14s):
Stephen comments on the way to represent quantities and volumes (16s):