only 3 c 2.AYellow cmpouid dissoved icuTor Hexanes is used as the eluant. After
ID: 550742 • Letter: O
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only 3 c
2.AYellow cmpouid dissoved icuTor Hexanes is used as the eluant. After 6.0 L of solvent has passed through the column, the yellow band still had not traveled down the column appreciably. What should be done to ensure the yellow compound is purified? Consider the following errors that could be made when running TLC. Indicate what should be done to correct them: 3. a. A two-component mixture containing 1-octene and 1,4-dimethylbenzene gave only one spot with an Rt value of 0.95. The solvent used was acetone. A two-component mixture containing a dicarboxylic acid and a tricarboxylic acid gave only one spot with an Re value of 0.05. The solvent used was hexane. When a TLC plate was developed, the solvent front ran off the top of the plate. b. c. 4. Calculate the Rr value of a spot that travels 5.7 cm, with a solvent front that travels 13 cm NAL NOTESExplanation / Answer
3)
a) In this two-component system, both compounds 1-octene and 1,4-dimethylbenzene are relatively least polar molecules.
Hence, if we want to separate this mixture, we need to use least polar solvent (not more polar solvent) and slowly
need to increase the solvent polarity to get the good separation of these compounds.
Hence, Hexane would be a good choice to start with and slowly increase its polarity by ethylacetate to get a good separation
of the above mixture.
In this case, the mistake is to choose the more polar solvent like acetone.
b) In this case, the mixture is not separated and not moved on the TLC. That means the solvent polarity is not enough to
move the mixture. Since the Rf value is only 0.05 (5%) using Hexane, it would be recommended to use 10% ethylacetate and 90%
hexane solution to run the TLC again. If it is an improvement in Rf value (~0.5), then is good. If not, you can still increase the
solvent mixture by 20% ethylacetate and 80% hexane and so on until you get a good separation.
C) If the solvent front is moved over the TLC plate, it is not a recommended to use it. Because it is difficult to make a conclusion
from this TLC. Sometimes, the spots are smeared or diffused and consequences would be inaccurate Rf values.
So, it is recommended to move solvent front up to 90% of the TLC plate hight.
4) Rf = The distance traveled by a given component /Distance traveled by solvent front
= 5.7 cm/13cm
Rf = 0.438
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