A student attempted to determine the identity of an unknown substance using thin

Question

A student attempted to determine the identity of an unknown substance using thin layer chromatography (TLC). The following data was obtained from several different experiments (all distances are in mm): Substance "A" Distance to the solvent front 69 Distance traveled by Substance "A" 28 Substance "B" Distance to the solvent front 82 Distance traveled by Substance "B" 45 Substance "C" Distance to the solvent front 73 Distance traveled by Substance "C" 48 Unknown Distance to the solvent front 51 Distance traveled by Unknown 27 Is it possible to identify the unknown from the data given? If so, identify it. and explain your reasoning. To be identified, the range of the unknown must overlap the range of one (and only one) of the known substances. For example, if the range of ratios for a comparison substance is 0.38 to 0.44, there is overlap. If the range of the comparison substance is 0.33 to 0.41, there is no overlap. Show your calculations and your reasoning clearly, specifically identifying what your mean by "overlap" or "no overlap".

Explanation / Answer

In TLC, the nature of unknown compound can be known based on their rentension factor (Rf) values

Rf = distance travelled by solute/distance travelled by the solvent front

For substance A , Rf = 28/69 = 0.405

For substance B , Rf = 45/82 = 0.548

For substance C , Rf = 48/73 = 0.657

For unknown substance , Rf = 27/51 = 0.529

From the calculated Rf values it is clear that the unknown compound may be B since their Rf values are very almost equal

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