NOTE: IS STUDYING \"TLC AND COLUMN CHROMATOGRAPHY\" IN OCHEM LAB 3. A student sp

Question

NOTE: IS STUDYING "TLC AND COLUMN CHROMATOGRAPHY" IN OCHEM LAB

3. A student spots an unknown sample on a TLC plate and develops it in dichloromethane solvent. Only one spot, for which the Rf value is 0.95, is observed. Does this indicate that the unknown material is a pure compound? What can be done to verify the purity of the sample? Two students were each given an unknown compound. Both samples contained colorless material The students used the same brand of commercially prepared TLC plate and developed the plates using the same solvent. Both students obtained a single spot of R 0.75. Were the two samples necessarily the same substance? How could they prove unambiguously that the samples were identical using TLC? 4.

Explanation / Answer

3. If a single spot observed on TLC with Rf value 0.95, when develop in dichloromthane It may not be necessarily a    pure compound. To verify the purity, TLC should be developed in some nonpolar solvent (or mixture of    solvents). Mixture of ethyl acetate and hexane with different percentage can be used. Compound will be    pure if one spot observed on all the TLC developed in different solvent systems. 4. To check if both the samples are same or different, one should do co-spot (application of both samples at same point) on TLC and develop them in different solvent systems. If both the samples are same, we observe a    single spot on TLC , else two different spots are formed if samples are not same.

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