1.
Pre-Lab Assignment Name Identification of Analgesics by Thin-Layer Chromatography 1. The
TLC plates we use are coated with silica gel. Which will move farther up the TLC plate, a polar
organic molecule or a nonpolar organic molecule? 2. A sample was run on a TLC plate using
95% hexane with 5% ethyl acetate as the developing solution. The Rr value of the sample was
found to be 0.05. What could you change in the experimental conditions to get a higher R, value?
3. A multiple unknown sample gives the following TLC plates with the unknown in the left
channel, the known in the right channel, and a cospot in the center channel. Which compounds
are present in the unknown?
Solution
1. On the TLC plate the non polar organic molecule will move further up than the polar organic
molecule. The polar compound bind strongly to the silica gel on the TLC plate, therefore it move
up very slowly. Where as Non polar compound bind weakly to silica gel on the TLC plate,
therefore it is able to move up more rapidly.
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