8, If the reference caffeine solution were made by dissolving caffeine in dichlo

Question

8, If the reference caffeine solution were made by dissolving caffeine in dichloromethane rather than methanol, how would this affect the Rf for caffeine? Explain. 9. Compound X has an Ry of 0.22 with hexane as the eluent. Using ethyl acetate as the eluent, would the Rr of Compound X be expected to be greater than, less than, or equal to 0.22? Why? 10. Predict the order of elution of a mixture of biphenyl and benzoic acid on a TLC plate in a 1:1 ethyl acetate:hexane solution. Would the order be different if the solvent system were changed? 11. Why is it important for the spots on a TLC plate to be above the level of the solvent in the TLC chamber? 12. Humans need some amount of UV light to induce the production of Vitamin D. However, excessive exposure to UV light is known to have harmful health effects. Describe the damage that UV light can cause as a result of both short-term and long-term exposure. What are measures to prevent damage from UV exposure in this lab? 13. List three possible safety risks specific to this experiment. Briefly describe precautions to address these risks.

Explanation / Answer

8. Methanol has a higher polarity than dichloromethane we know that Rf increases with the polarity of the solvent so if you originally are using methanol and now you want to use dichloromethane then you can expect the Rf to decrease

9. Rf will be greater than, because ethyl acetate has a greater polarity than hexane

10. Benzoic acid is a Carboxylic acid therefore it has a higher polarity than biphenyl, so biphenyl will elute first followed by the benzoic acid. This would not change if you change the solvent system

11. if the spots are below the level they will be dissolved

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