virtual lab: chromatography [35 points; 5 points / question in purple]


introduction / prelab

This virtual laboratory activity is based on investigation 5 in your AP chemistry lab manual and the handout of the in-person lab. While Investigation 5 refers to paper chromatography, this lab will use column chromatography; the basis / rationale of both chromatography techniques are based on an understanding of intermolecular forces. questions:

1. what is a simplistic basis of adsorption chromatography, where you ignore the role of the solvent molecules in the mobile phase; include / define the terms, stationary phase, and mobile phase in your response. exploring the simulation may provide an insight into the process.   hint: see an  animation of  the chromatography process on a molecular level.

2. describe isocratic versus gradient eluation. ?

3. MSDS data on isopropyl alcohol

questions regarding the column chromatography laboratory results shown in the video (~ 14" duration). record your observations.

4. based on concepts involving IMF, rationalize the basis of the successful separation of the red / blue dyes. specifically, rationalize why both dyes were not eluated from the column using a low concentration of alcohol, while the second dye was eluated with a higher concentration of alcohol. hints:  the rationale is more complicated than your response to questions 1; you'll have to evoke the role of the alcohol molecules in the process; e.g. alcohol is like a competitive inhibitor. additional hints: read about reverse phase chromatography and analyze the chemical structures of the various chemicals used in the lab.

supplemental questions: see pp. 46 - 47 in the AP chemistry lab manual (investigation 5) in regards to Rf  , which is shown in a video (~ 9:30 duration) of a paper chromatography lab.

5. what is Rf ? include a drawing / sketch to clarify your answer; hint: video (view ~ 6 - 6:30)

6.  If you did the in-person lab, you would observe:

     a.  5 % isoproply alcohol would eluate only the red dye

     b.  15 % isoproply alchol would eluate the red dye, then the blue dye

     c.  70 % isoproply alcohol would simulataneously eluate the red and blue dyes 

justify / rationalize your response using concepts of IMF and clearly identify the molecules (red dye, blue dye, alcohol molecules, and stationary phase molecules) involved in the IMF.  hint:  see your response to question # 4

7. what would be the relative value of Rf for the red and blue dye (provide approximate numeric values) using a reverse phase stationary phase and ___ isoproply alcohol mobile phase in a paper chromatography lab ?  hint:  see your response to question # 6.   

a.   5%

b.  15 %

c.   70 %