[Benzoic Acid]

   A TLC plate showed two spots of Rf 0.25 and 0.26. The plate was removed from the developing chamber, dried carefully, and returnted to the developing chamber. What would you expect to see after the second development was complete?

-Would the Rf values double if it were placed into a developing chamber twice? The only bad thing that I'm aware of, which comes from exposing the plate to air, is the evaporation of the solvent...

Why might it be very difficult to visualize the separation of cis- and trans- 2-butene by thin-layer chromatography?

I have no idea on this one, I seached my lab book twice and it doesn't even mention steroisomers, or isomers of any kind with regards to TLC.

thanks  

[hereafter]

Trans and cis is really hard to seperate. I have the same problem to deal with. Now I am thinking florisil column. Does anybody know what's the difference between florisil and silicon gel about purification?

[movies]

Florisil is less polar than silica gel.  Alumina is another alternative solid phase: it is more polar than florisil, but less polar than silica gel.

A nifty trick for separating olefin isomers is to use silver impregnated silica gel.  A couple of people in my lab have used that and had great results.