Briefly explain the problem a student might encounter if the following procedura

Question

Briefly explain the problem a student might encounter if the following procedural changes were made while performing this experiment. Instead of using a pencil, the student marked the location of the dye spots with a pen. The student neglected to cover the chamber while the mobile phase solution ascended the plate. The student was late starting the experiment, and allowed the solvent front to move only 20 mm up the 7.5-cm TLC plate. The two components in the mixture, A and B, had R_f s of 0.40 and 0.60 respectively. The student ran out of mobile phase solution after testing the samples but before testing the FD&C; dye standards. Because the isoamyl alcohol bottle was empty, the student made the new mobile phase solution using an 8:1:2 mixture of 95% ethanol, concentrated NH_3 solution, and water.

Explanation / Answer

Q1

1

if you use pen, those have plenty of dyes, therefore they will interfere and interrupt the Rf values of the samples

2

if he did not covered, the mobile phase might evaporate, therefore Rf values are decreased

3

the Rf diffference will not be the same of the Full time experiment vs. the rushed experiment

the Rf ratios are not reliable since they can go furrther more (to the top)

4

note that isoamyl alcohol is not that polar... compared to ethanol

the ethanol, NH3 and water mix are much complex than thte isoamyl, so expect different Rfs vlaues

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