Name:

Section:

1. The experiment.
2. The appropriate or assigned sections of your textbook.

1. A TLC experiment is performed. When the solvent advances up the plate by a distance of 4.20 cm, it is found that substance X moves up the TLC plate a distance of 2.62 cm. What is the R_f value for substance X?
2. In most cases the solid substance on the TLC plate (called the "stationary phase") is quite polar. Often it is SiO₂, called silica gel, which is actually very clean and finely ground sand. Polar substances tend to interact quite strongly with the polar stationary phase and so can be moved up the plate only by using a very polar solvent. Nonpolar substances interact weakly with the silica gel and move up the plate readily with nonpolar solvents. Suppose you have a mixture of the following solids: iodine (I₂), benzophenone (H₅C₆-C(=O)-C₆H₅), benzoic acid (C₆H₅-C(=O)-OH), and oxalic acid (HOOC-COOH). Click for structures. You dissolve a small quantity of the solid mixture in ethanol and spot the solution on a TLC plate. You develop the plate using carbon tetrachloride, CCl₄. Which of the 4 substances should have the largest R_f value? Which the smallest?
3. A mixture thought to contain some or all of compounds A, B, C, and D gives the following TLC on silica gel developed with ethanol:
   
   

   Expected R_f values for A, B, C, and D are 0.13, 0.27, 0.46, and 0.77 respectively. What can you conclude about the mixture based on its TLC? Which compounds may be present?
   Hint: Calculate R_f values of the spots on the developed TLC plate provided.