Given that the surface of a silica coated TLC plate (the type we use) can be represented by the structure below, would 9-fluorenone or benzoic acid be more attracted to the TLC plate surface?
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Part 1: Choosing the best developing solvent for TLC 1. Draw the bond-line structures of the two solids you separated, 9-fluorenone and benzoic acid. Which is more polar? 2. Given that the surface of a silica coated TLC plate (the type we use) can be represented by the structure below, would 9-fluorenone or benzoic acid be more attracted to the TLC plate surface? 3. In our Ochem labs, two solvents are often used for developing TLC plates: ethyl acetate and hexanes. Draw the bond-line structures for these two solvents. (Just draw one isomer of hexane). Which of these solvents is polar and which is nonpolar? 4. As you learned in the tutorial video, "TLC Theory", how fast a compound moves up a plate is determined by its solubility in the mobile phase (developing solvent) vs its attraction to the stationary phase (silica). If a nonpolar solvent is used, would you predict 9-fluorenone or benzoic acid moves up the TLC faster? If a moderately polar solvent is used, would you predict 9-fluorenone or benzoic acid moves up the TLC faster? Explain your answers using the relative polarity of silica, developing solvent, 9-fluorenone and benzoic acid. 5. Consider the photo below showing TLC plates from a different experiment. Which plate shows the best separation for the four different compounds that were spotted? Explain.
Sri K.
2. The material (solid phase) of the TLC plate is a silica gel, which is a polymer of SiO2 units. a. What intermolecular forces does the silica gel participate in? b. What three functional groups would be attracted to it? c. Would you expect the solid phase to be attracted to our two compounds (Fluorene and Fluorenone), why? 3. In the second half of the lab, we will be comparing analgesic tablets. Write the active ingredients for the following tablets: Tylenol, Advil, Excedrin, and Midol. b. For the active ingredients, write the ingredients from most polar to least polar.
Adi S.
Given the structures of benzophenone and biphenyl (shown below), answer the following questions: 1. Which of the two structures is more polar and explain why? 2. Which structure would be expected to have a higher Rf value on a polar TLC plate (ex: silica, alumina) and why? 3. Why is it recommended to spot the analyte on the TLC plate in a position that it will not be immersed in eluent solvent (Figure A)? What is wrong with figure B?
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