Question

The diagram above shows a thin-layer chromatogram of a mixture of products from a chemical reaction. The separation was performed using 50% ethyl acetate in hexane as the solvent (mobile phase) and silica gel as the polar stationary phase. On the basis of the chromatogram and the information about solvents in the table above, which of the following would be the best way to decrease the distance that the products travel up the plate? OA Use pentane instead of hexane in the solvent. B Decrease the percentage of ethyl acetate in the solvent. C Increase the percentage of ethyl acetate in the solvent. D Add up to 5% methanol to the solvent.

Answer 1

the correct answer is B. Decrease the percentage of ethyl acetate in the solvent. Ethyl acetate is a polar solvent with a dielectric constant of 6.02, while hexane is a non-polar solvent with a dielectric constant of 1.9. By decreasing the percentage of ethyl acetate, the polarity of the mobile phase will decrease, and the products will travel less up the plate.

Answer 2

To decrease the distance products travel up a TLC plate, decreasing the percentage of ethyl acetate in the solvent is the best choice as it reduces the solutes' affinity for the polar mobile phase, which consists of 50% ethyl acetate in hexane, and increases interaction with the polar silica gel stationary phase.

Step-by-step explanation:

The chromatogram in question was generated using a thin-layer chromatography (TLC) method with a silica gel stationary phase and a 50% ethyl acetate in hexane solvent system. To decrease the distance that the products travel up the plate, one needs to alter the solvent system to decrease the solutes' affinity for the mobile phase and increase their interaction with the stationary phase.

Option B, which suggests decreasing the percentage of ethyl acetate in the solvent, would be the best way to achieve this. Since ethyl acetate is a polar solvent and silica gel is a polar stationary phase, reducing ethyl acetate's concentration will decrease the solutes' mobility, thereby decreasing the distance they travel up the TLC plate. In contrast, Option A (using pentane) would likely not affect or might even increase the distance traveled, as pentane is less polar than hexane and would not significantly change the solutes' affinity for the mobile phase. Option C would actually increase the polarity of the mobile phase, leading to a greater distance traveled. Option D (adding up to 5% methanol) would increase the solvent's polarity too much, causing stronger solute-mobile phase interactions and greater travel distances.