Homework Help: science(chem)

Posted by ~christina~ on Tuesday, May 5, 2009 at 7:53pm.

I have a question about compounds that oil out of solvents after drying.

How would I analyze this? Could I make a KBr pellet, or would I just be able to analyze it in UV spec?

I assume that the solvents used to dissolve the compound, would be used as a blank, right?

I tried to dry off the solvent used to dissolve the compound and it wouldn't completely dry off, and this is why I think it was oiling out of solution. I was originally planning on trying extraction after drying off the compound. I had no choice but to try to go and re-dissolve the compound in a solvent (CH2Cl2). It looked like it dissolved, but I'm not sure since the pasteur pipette looked as if it had an oily residue after I pipetted the solution over to another container....

Not sure what to do now,
Thank you

science(chem) - DrBob222, Tuesday, May 5, 2009 at 10:16pm
I have no idea what "oiling out of solution" means. Sure you can make a KBr pellet. AND you can run the sample on a UV. Can it be that part of the unknown dissolved in CH2Cl2 and the "oil part" was another compound? If I thought some had dissolved in CH2Cl2, I would attempt to recover the part that dissolved. That could be a pure component.
science(chem) - ~christina~, Tuesday, May 5, 2009 at 11:25pm
I dried a solution of solvent + unknown compound dissolved in it, and it would not fully evaporate off and leave a residue. What was left over no matter how much I heated the watchglass was stagnant droplets as if I was using dirty glass and I had poured a solution over it. (i.e. diry volumetric flask after pouring solution out, has stagnant droplets of water)

I'm not sure if the oily substance was another compound. Hopefully it is not. I ran a plate and it showed 1 strong spot and 1 weak weak spot and my prof. said that it looks like it is one compound. This is the reason I tried to evaporate off the solvent and see if I could just see one compound or 2 after using this to spot another plate, therefore elminating the chance that it is solvent interaction that is causing the second spot.

I will try to analyze the CH2Cl2 with the unknown in it and see what happens.

Thank you Dr.Bob

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