Name(s): ___________________________________

TLC Analgesics Lab: Final Report Questions


Answer the following questions and attach to final lab report.

1.     Consider the following silica gel TLC plate of compounds A, B, and C developed in n-hexane:

a) Determine the R f values of compounds A, B, and C run on a silica gel TLC plate using n-hexane as the solvent.

b) Which compound, A, B, or C, is the most polar?

c) What would you expect to happen to the respective  R f values if you used acetone instead of n-hexane as the eluting solvent? Circle one for each compound.

A

Increase or Decrease or Remain about the same

B

Increase or Decrease or Remain about the same

C

Increase or Decrease or Remain about the same

d) How would the R f values change if eluted with n-hexane using an alumina TLC plate?

A

Increase or Decrease or Remain about the same

B

Increase or Decrease or Remain about the same

C

Increase or Decrease or Remain about the same

2.     Consider a sample that is a mixture composed of biphenyl (bip), benzoic acid (bac), and benzyl alcohol (bal). The sample is spotted on a TLC plate and developed in an ethyl acetate solvent mixture. Predict the relative order of the R f values for the three compounds in the sample.

______ > ______ > ____

 


3.     You are trying to determine a TLC solvent system that will separate the compounds X, Y, and Z. You ran the compounds on a silica gel TLC plate using n-hexane/ethyl acetate 95:5 as the eluting solvent and obtained the chromatogram below. Describe how you could you change the system to give better separation of these three compounds?

4.     A student ran a TLC of the reaction mixture of an organic reaction on a TLC plate using acetone 30 minutes after mixing the reactants and obtained the result below. The student was synthesizing an ester and had mixed an alcohol (R f = 0.33) with a carboxylic acid derivative (R f = 0.66). Explain the results and if the reaction is complete or if student should continue to wait longer before working up the reaction. Also, comment on the quality of the chromatogram and how it could be improved. 

5.     A student spots an unknown sample on a TLC plate. After developing in n-hexane/ethyl acetate 50:50, A single spot was observed with an R f of 0.55. Does this indicate that the unknown material is a pure compound? What can be done to verify the purity of the sample?

Plate A, below, represents the TLC chromatogram of a compound run in hexanes. The same compound was then spotted on a large TLC plate and again run in hexanes. Which TLC plate, B, C, or D, correctly represents how far the compound would run on the longer plate?

6.     Find the recommended single adult dose (a.i.) for aspirin, ibuprofen, and acetaminophen. Complete the table below, ranking the analgesics in order of increasing biological activity based on their respective doses.  Calculate the millimoles (mmol) that corresponds to the dose for each analgesic. (Show one example of your calculation below the table.) Enter the mmol values in the table. Rank the analgesics again in order of increasing activity based on mmol of active ingredient per dose.

Analgesic

Dose (mg)

Dose (mmol)

aspirin (ASP)

 

 

acetaminophen (ACE)

 

 

ibuprofen (IBU)

 

 

Rank:

__ < __ < __

__ < __ < __

Calculation (mmol):

 

7.     Calculate how many tablets of “extra strength” Tylenol could be produced from 5.0 kg of active ingredient if each tablet contained 1 dose. Show your calculation.