Organic Chemistry Lab - Thin Layer Chromography Question

[WorcesterPHOBoy]

Anyone know what is the answer to this question, I could not find the answer to it:

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

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[eddie13231]

Ok so first question in where are your two compounds after the TLC plate has dried? They are in their original position of 0.25 or RF of .25 or whatever. So if both compounds moved 0.25 during the first TLC then they should move another 0.25 as long as the mobile phase doesn't change during the second(RF of 0.5). I hope this helps and I think this is correct.

 

[sarahjth]

Yep, Eddie hit it right on the nail! 😀

 

[ersoco]

Anyone know what is the answer to this question, I could not find the answer to it:

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

An Rf of .25 (or .26) means that the mobile phase carries the compound (the spot) for 25% (or 26%) of the distance that the mobile phase and the compounds are in contact. So for the second development, the mobile phase and the compound are only in contact for 75% of the TLC plate, so the extra distance moved will be .75*.25 which is .1875, so it will have a total Rf of .25+.1875 or .4375. Likewise .26+(.74*.26) = .4524. So the spots get a little more separated. Hope this helps.
I’m actually an organic lab TA and I work in an organic research lab and have run a few hundred TLC’s the past year.