chromatogaphy Post lab questions 1. You are trying to determine a TLC solvent sy
ID: 543499 • Letter: C
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chromatogaphy Post lab questions 1. You are trying to determine a TLC solvent systemm that will separate the compounds A, B, and C. You ran the compounds on a TLC plate using hexanes/ethyl acetate 1:1 as the eluting solvent and obtained the chromatogram to the right. How could you change the solvent system to give better separation of these three compounds? 2. Consider a sample that is a mixture composed of biphenyl, ethyl benzoate, and benzyl alcohol. The sample is spotted on a TLC plate and developed in a hexanes/ethyl acetate solvent mixture. Predict the relative R f values for the three compounds in the sample. 3. If you are trying to separate a mixture of three compounds and all of the spots on a TLC plate are near the solvent front, would this be a good solvent to use for separation? What could you do to the mobile that would allow for a better separation? 4. What would happen to your column if you let the solvent drop below the top layer of sand? Explain.Explanation / Answer
1) As the chromatogram is shifted to the right side ,the retention time of the compounds in te eluting solvent must be higher,due to low solubility.
hexane(non-polar)+ethyl acetate(polar) are in 1:1 in the solvent, so does not dissolves polar compounds to greater extent.So, taking a slight polar solvent(like alcohol in place of ethyl acetate) would increase the solubility of polar compounds A,B,C.Or increase the amount of polar ethyl acetate so that hexane :ethyl acetate is 1:2 or higher.
This will decrease the retention time of the compounds and let them separate from the eluting solvent.
2) Most polar benzoic acid will be least soluble in non-polar eluting solvent system ,so move least distance up the chromatogram, so least Rf value.
Next benzyl alcohol of intermediate polarity will have intermediate Rf,and non-polar Biphenyl will have the highest Rf value.
Rf=distance travelled by compound/distance travelled by eluting solvent
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