2 EXPERIMENT 2 3 Pre-Lab Questions 1. The structures of the two main pigments, l

Question

2 EXPERIMENT 2 3 Pre-Lab Questions 1. The structures of the two main pigments, lycopene and -carotene, are shown in the Background section. igments are examples of alkenes. What functional group present in these molecules allows for this classification? d these compounds dissolve in hexane, a nonpolar solvent, or water, a polar solvent? b. Woul Explain your answer. 2. You are asked to mark the chromatography paper with a pencil and not with a flair or ink pen. Why does this make a difference? 3. Why is bromine a good reagent to use in this experiment? 4. What is the "Re value"? How is it determined? 5. This experiment uses two systems of chromatography; name the two systems

Explanation / Answer

1. The pigments lycopene and b-carotene are

a. have polyunsaturated systems. That is have highly conjugated double bonds in it.

b. These compounds are hydrophobioc in nature and thus would dissolve in hexane.

2. ink pen has ink which also moves when comes in contact with mobile solvent. Therefore pencils are used when makring tlc plates as it has graphte which does not dissolve and move like ink.

3. Bromine adds to the double bonds and thus can tell us information about degree of unsaturation. Thus bromine is a good reagent.

4. Rf value is distance travelled by the solute upon distance travelled by the solvent on the tlc plate. It is measured by a scale on the tlc plate and Rf is calculated after tlc is done.

5. The first is thin layer chromatography or tlc and the second is column chromatography.

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