2-Post lab questions Thin layer chromatography is routinely used to monitor the

Question

2-Post lab questions Thin layer chromatography is routinely used to monitor the progress of a reaction. The following TLC was performed for a certain reaction. Discuss the progress of the reaction.(SM starting material, P products, RXN reaction mixture) (1 point) 2. The following TLC experiments were not performed properly discuss that (1.5 points 3. A line about 2 cm from the edge of TLC plate must be drawn using a pencil, but not a pen. Why? (1 point) 4. What are the main uses of TLC experiments, discuss each of them (1 point) 5. A student spotted the following three compounds on a TLC plate and developed it. Match each spot with the corresponding compound. Explain your choices. (1.5 point) ??

Explanation / Answer

1.The TLC indicates that the reaction is complete as there is no spot corresponding to unreacted reactants .

2.A) In A the spot has not moved much from the base line or from the point of spooting which means that the mobile phase is not of correct polarity to move the component.

2.B) In B the spots are spread , this can happen either due to too much concentration of the spoting mixture or may be a problem with the mobile pahse.

2.C) In C , the distance travelled by the component and distance travelled by solvent front is too close and this will affect the calculated Rf value as Rf value= Distance travelled by component/Distance travelled by solvent front.

3. Base line should be drawn using a pencil as the ink of the pen may also separate and appear in the TLC plate causing errors.The spot due component of ink may be mistaken as a spot of the component in reaction mixture if they have the same Rf value.

4. Main uses of Thin Layer Chromatgraphy

5. The compounds spotted are that of p-hydroxy benzoic acid , p-methyl benzoic acid and p-isopropyl toluene, among these the spot which has moved longer distance is that of isopropyl toluene as it is least polar , the second one is that of p-methyl benzoic acid and the spot which has travelled least is that of p-hydroxy benzoic acid due its polarity due to intermolecular hydrogen bonding ,it gets more adsorbed on the polar silica(stationary phase) and travels less with the mobile phase.

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