Tlc questions

Topics: Thin layer chromatography, Chromatography, Benzene Pages: 2 (567 words) Published: September 23, 2013
Post lab Questions
1. 3-decanone will have a higher Rf value than 3-decanol, toluene will have a higher Rf value than benzoic acid, and cyclooctane will have a higher Rf value than cycloctanone. This is because they are not as polar as the compounds with lower Rf values, the compounds that are most polar tend to stay longer with the polar adsorbent, while the least polar compound travels with the eluent that is lower in polarity. 2. TLC in today’s experiment stands for Thin Layer Chromatography. 3. From least polar to the most polar:

Heptane-Toluene-Acetone-Methanol-Acetic acid
, , , ,
4. The Rf (Retardation factor) is the ratio of the distance that the compound/mixture traveled to the distance the solvent/mobile phase traveled. 5. From least Rf to the highest Rf:
Benzoic acid – Benzaladehyde - n-Decane
If the TLC were run with a more polar solvent, all the samples will run too quickly with the solvent front, therefore no separation will be achieved. 6. The molecular weights of the analgesics used in this lab are as follows Analgesic Name

Molecular weight (g/mol)
Aspirin
180.17
Acetaminophen
151.10
Ibuprofen
206.29
Caffeine
194.19

7. A 500 mg tablet of Tylenol contains 3.31x10-3 moles of acetaminophen. 8. A 50/50 mixture of dichloromethane and ethanol was added to the crushed analgesic tablets to fully dissolve the tablets because the whole tablet will not dissolve as it contained not only the analgesic, but also binders, buffering agents and other components that would not make the tablet to fully dissolve in just a polar solvent. 9. It is advisable to mark the TLC plate(s) with a pencil instead of a pen because the ink from the pen might move up the plate along with the substances being separated which would contaminate and spoil the substances being examined. Since a pencil is made from graphite and graphite is not aqueous (in solution, i.e. it is dry) it will not adsorb or move up the plate. 10. A small concentrated...
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