Polar..Non-polar...caffeine...aspirin..

[nacho]

Hi, I have a question:

Which is more polar; caffeine, aspirin or paracetamol?
In TLC, caffeine has the lowest Rf value when the stationary phase is silica and CaSO4, and the mobile phase is Butyl Ethanoate and Trichloroethane.
I'm struggling to work out which ones are polar and which are non-polar, and why they adsorb and desorb the way they do.

also, a follow up qeuestion:
Why would water be an unsuitable mobile phase for this experiment?

it's all so damn confusing...so damn confusing

[jane1234]

I think that the caffiene would be the most polar, as it is more attracted to the stationary phase (which is also polar) and not so much the mobile phase (which is non-polar). As it has the lowest Rf value, it moves the least which means the caffiene was the one most attracted to the polar stationary phase (more than the others). Given the "like dissolves like rule" ... a more polar substance will be attracted to the polar solvent more than a less polar substance.
Hope that made some kind of sense... anyone please correct me if I'm wrong...

[nacho]

would you think i would score marks if i commented on the crystalline structure of caffeine, and that it had the lowest Rf because of it's strong intramolecular forces (which disallowed it to form many from the solvent)?
I also thought all three substances were to an extent, polar?

[Water]

Caffeine would be the most polar correct, because it is the most strongly adsorbed to the stationary phase


I"m guessing Water can't be used because it won't offer any different colourings  so you wouldn't be able to detect the seperations.

[jane1234]

Or else because water is polar as well ... and the caffeine would be attracted to the mobile phase AND the stationary phase?? Therefore it probably wouldn't indicate the most polar substance.
Or maybe just what Water said as well...

[jane1234]

would you think i would score marks if i commented on the crystalline structure of caffeine, and that it had the lowest Rf because of it's strong intramolecular forces (which disallowed it to form many from the solvent)?
I also thought all three substances were to an extent, polar?

They are... it's asking for the MOST polar.
And I think you might get some credit for that ... as long as you mentioned the polarity of the stationary and mobile phases.

[Water]

Which is more polar; caffeine, aspirin or paracetamol?
In TLC, caffeine has the lowest Rf value when the stationary phase is silica and CaSO4, and the mobile phase is Butyl Ethanoate and Trichloroethane.
I'm struggling to work out which ones are polar and which are non-polar, and why they adsorb and desorb the way they do.



WAIT A MINUTE,


COFFEE would be the least polar,


If the sample is polar, and the mobile phase is polar, then it'd have the highest RF Value as it will desorb more often than adsorb to the stationary phase.





So it'd leave aspirin and Paracetamol. Sorry , I"m really busy atm, but thats just my 2 cents atm!



My guess is aspirin though.

[jane1234]

Which is more polar; caffeine, aspirin or paracetamol?
In TLC, caffeine has the lowest Rf value when the stationary phase is silica and CaSO4, and the mobile phase is Butyl Ethanoate and Trichloroethane.
I'm struggling to work out which ones are polar and which are non-polar, and why they adsorb and desorb the way they do.



WAIT A MINUTE,


COFFEE would be the least polar,


If the sample is polar, and the mobile phase is polar, then it'd have the highest RF Value as it will desorb more often than adsorb to the stationary phase.





So it'd leave aspirin and Paracetamol. Sorry , I"m really busy atm, but thats just my 2 cents atm!



My guess is aspirin though.

Trichloroethane is non-polar, and I think the other one is (as it is an ester)
So the mobile phase is non-polar.

And the stationary phase is polar because silica is polar.

I think that's right ... not 100% sure...

[Water]

Ahh sorry my mistake  :buck2: