2- I want you to form a hypothesis regarding the separation of the chemicals. Dr

Question

2- I want you to form a hypothesis regarding the separation of the chemicals. Draw a plate below that outlines what you think the chromatograph will look like for the four single compounds. Look at the provided structures and determine what you think is the relative polarity of the compounds, and place the m on the plate accordingly. Explain why you picked the order of chemicals that you did regarding polarity.

3- You have a chromatogram that have two spots on it, spot 1 moved 15 mm from the origin, and spot 2 moved 35 mm from the origin. The solvent moved a total of 57 mm. What are the Rf values for the two chemicals? Which is more polar?

Explanation / Answer

In order to answer question 2, I need to know the chemical structures of the molecules.

3) Distance travelled by the solvent (solvent front) = 57 mm.

Distance travelled by compound 1 = 15 mm.

Distance travelled by compound 2 = 35 mm.

Retardation factor (or retention time), Rf = (distance travelled by compound)/(solvent front)

For compound 1, Rf = (15 mm)/(57 mm) = 0.263 (ans)

For compound 2, Rf = (35 mm)/(57 mm) = 0614 (ans)

In TLC, the stationary phase is polar (silica or alumina) while the mobile phase is less polar (a combination of a non-polar solvent like hexane with a polar solvent like methanol, etc). Therefore, polar compounds interact more with the polar stationary phase and are strongly retained on the plate while less polar compounds move up more easily. Since compound 1 has a lower Rf value, therefore, 1 is the more polar compound.

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