(5) Discuss the purity of your crude and recrystallized aspirin based on the TLC
ID: 847515 • Letter: #
Question
(5) Discuss the purity of your crude and recrystallized aspirin based on the TLC data. Suppose that you were concerned that an additional spot in the TLC of your purified aspirin might be salicylic acid. Discuss how you could use TLC to determine whether the additional spot was salicylic acid. (6) Did the Rf value for commercial aspirin match any spots on your TLC? How could Rf be used to identify a compound? (7) Analyze the HPLC of your aspirin for information regarding its purity. Do you see impurities that are not observed by TLC? If you worked for a company that sold aspirin commercially, would HPLC or TLC be the best way to analyze the purity of the aspirin that was being synthesized? Briefly explain your answer.Explanation / Answer
a) You could calculate the Rf for the spot. The Rf is calculated by dividing the distance the spot traveled from the origin, divided by the distance traveled for the solute. You'll need to find the Rf for the particular solvent you're using, usually something like NaOH. Rf values are reference values that are universal for the solutes, so it's something you could compare to known data. You could also conduct the same experiment for with salicylic acid and compare the Rf values if you have the resources.
b) Rf values will match another repeated experiment if all the variables are the same, like if you're using the same mobile phase and the same thin layer material. It's an easy way to identify a compound. If the Rf you get matches one for something you believe could be in the compound you're testing, it can give you a good idea if it is present or not.
c) HPLC is a LOT better at seeing things that are there minimally, and would be much more ideal if you have access to it. Thin layer chromatography is used if there's a decent amount of all the compounds. If there's not enough of one of the compounds, there's a pretty good chance you won't be able to see it, especially if you aren't able to stain the compound.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.