Question

3. TLC analysis of an unknown sample using pure ethyl acetate as a developing solvent gives a single spot with an Rf value of 0.08 1 points A. Explain why this result does not guarantee that the sample is a pure compound. B. Suggest two changes that could be made to the experiment to improve the analysis of the unknown sample. 2 points Change 1 Change 2

Answer 1

solution: The given condition is that the unknown sample run in pure ethyl acetate as a solvent for TLC system to give Rf - 0.08 This result does not guarante that the sample is a pure comp- because in ppure ethyl acetate the spot lift only 0.08 Rt It the unknown sample contain polar impurity then that polar impunts st be at bottom in ethyl acetate solvent system. It will in ethyl acetate. For that you have to change solvent system from ethyl acetate to more polar solvent system. spot lift only 0.08 Rf value- not lift in ethyl acetate. For ® For to improve the analysis of unkown sample to change ② Use polar solvent system se 5%. Me oll: Dcm, 57. Meohich cz product Rf value 10%. Me oltiDcm, 10%. Meolti chelz. If still the bot Is less than 1 then add 2-3 drop of triethyl amine on aqueous ammonia into solvent system For analysis of unkown sample the Rf value of unknown sample on The should be a 4-5 so that you can see on TLE is there any polar impunities. 2 Once the The is well develop by using appropriate solvent system, then use different staining reagent ne Iodine, kmnou, 2.4 DNP, Anisole, etc. If the unknown sample is uv active but by using different staining reagent you will get tv information of uw inachi impurities. If unknow sample is ur inactive then must use staining reagent.