This lab report (and all lab reports you write for this class) should follow the

Question

This lab report (and all lab reports you write for this class) should follow the guidelines given in the Writing Lab Reports" chapter of the Handbook. In addition to these guidelines, most experiments will specify additional topics to discuss. For this particular experiment, your conclusions should include: .Report which of the unknown analgesics you were given, based on TLC and melting point. . Calculate Rs of all spots, and explain the differences in results of the two different solvent systems List the four known analgesics in order of polarity. Address how pure your compound was, based on its melting point and TL.C . Report whether or not the pain reliever tablet had the analgesic reported on the label. 1) Consider the following silica gel TLC plate of compounds A, B, and C developed in hexanes: 5 cm- 4cm- 3cm 1cm- A B C 0 cm- a. Determine the Revalues of compounds A, B, and C. b. Which compound is the most polar? c. What would you expect to happen to the Ri values if you used acetone instead of hexanes as the eluting solvent? d. How would the R values change if eluted with hexanes using an alumina TLC plate? 2) What could happen if you used ink to draw in your base line and letters on the TLC plate? 3) What could happen if you spot too much of a compound on the TLC plate? 4) What would happen if your solvent level is above the level of the initial spots? 5) The CRC lists the melting point for a compound as 182-1839C. You observe a melting point for s same compound isolated in your experiment as 177-181°C.What can you conclude about the compound isolated in your experiment?

Explanation / Answer

1)

a) Rf = distance travelled by solute / distance travelled by solvent

So, for A, Rf = 2 cm / 4.5 cm = 0.44

For B, Rf = 4cm / 4.5 cm = 0.88

For C, Rf = 3.5 cm /4.5 cm = 0.77

b) Stronger a compound bound to the adsorbent due to strong attraction with TLC plate, the slower it moves up the TLC plate Therefore,  Compound A is the most polar.

c) Acetone is more polar than hexane, so it will increases the compounds Rf value.

d) Alumina is more polar than silica therefore each compound move slower on the alumina TLC plate and thus compounds have lower Rf values.

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