Question

Pre

-Laboratory Assignment

1.

Briefly describe or define each of the following terms as they pertain to this experiment.

a) Spotting a plate

b) Developing a plate

c) Visualizing

d) Rf

e) eluent

f) stationary phase

2. List the following solvents in order of increasing polarity: dichloromethane, acetone, toluene and

cyclohexane.

3. Your unknown sample moved a distance of 25 millimeter from its origin while the distance

traveled by the eluent from the origin was 55 millimeters. What is the retention factor of your

unknown?

4. How can you show that two compounds are the same using TLC?

5. What are the two most commonly used adsorbents used in TLC and column chromatography?

6. Draw a chromatogram showing an Rf of 0.75 including its origin, distance traveled by both the

compound and eluent. Include an equation for the calculation.

Answer 1

I'm going to answer number 2, since the first one is more of a research type of question.
The order would be: Ciclohexane < Toluene < Dichloromethane < Acetone
This is due mainly to the structures of each:

As you can see, the ciclohexane has no polarity at all, followed by toluene, which has a CH3 group attached, as well as resonance, that confers it with a bit more polarity. Then follows the dichloromethane, with reactive chlorides attached, that can also increase polarity. And finally, acetone, which is highly polar due to the electrodensity produced by the oxygen and where it is located.

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