Question

4) You purify two colorless solids (2 and 3) by recrystallization. Both have a melting point range of 102-104 °C. You forgot to label your work, so you are not sure which solid is 2 and which is 3. You have a small amount of an authentic sample of pure 2 available in your lab. How can you identify the unknowns?

Answer 1

If one has an authentic sample of Pure sample 2 by Thin Layer Chromatography (TLC), one can identify which sample is 2 and which is 3 from a mixture having both 2 and 3 samples.

For this one has to dissolve the little amount of mixture (containing both samples 2 &3) in a suitable solvent. The authentic sample of 2 also should dissolve in a suitable solvent (little amount).

Then one has to spot this two on a TLC plate as two separate spots and has to elute them in a mobile phase in a TLC chamber.

Upon seeing the TLC plate on UV light one can identify which compound is 2 and which is 3 (the mixture having 2 and 3 if they have different R_^f (retardation factor) values one of them will match with the authentic sample of 2).