eading edge (top) or the spot_-not rrom its center, as is customary in 1. A stud

Question

eading edge (top) or the spot_-not rrom its center, as is customary in 1. A student spots an unknown sample on a TLC plate and develops it in dichlo- romethane solvent. Only one spot, for which the R, 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? 2. You and another student were each given an unknown compound. Both sam- les contained colorless material. You each used the same brand of commer- cially prepared TLC plate and developed the plates using the same solvent. not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

Explanation / Answer

Part 1 and 2- Having one spot does not indicate a pure compound because we can easily have two compounds that have identical or indifferentiable retention factors in the solvent system of our TLC; regioisomers and diastereomers commonly fit into this category. We can also have two or more spots on top of one another that only looks like one spot.

One can try changing the solvent system to see if there is any distinct spot developed. For example, rf for two different compounds can be different in water and methanol.

Some spots will be visible only in UV light.

Part 4- Rf value is the ratio of distance traveled by the compound to distance traveled by the solvent.

Hence Rf = 5.7/13 = 0.438  

Part 6- To visualize Alkyl halide spot, AgNO3 can be used as a spray reagent

DNP (Dinitrophenylhydrazine) can be used for ketone as well as aldehyde

Ninhydrin for amino acid

and phenylhydrazine for sugar

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