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    Please can anyone help me with this?

    I have a weak base and a weak acid, I place a mixture of the acid/base into a separating funnel with an organic solvent and shake. A sample of this is analysed by tlc and shown to contain both the acid and the base.

    Then with the rest of the acid, base and organic solvent I add dilute HCl into the separating funnel and shake. I removed the lower aqueous layer and placed into another separating funnel. (Now here I assumed that the base became protonated because of the HCl and so partitioned into the aqueous layer, is that correct?)

    This aqueous layer HCl solution is then neutralised with dilute NaOH, enough is added make it alkaline. More organic solvent is added and it is shaken and left to separate. The aqueous layer is removed and set to one side, the organic solvent layer is removed and analysed by tlc to show it contains acid.
    That's the part that I am confused about, can anyone explain it to me please?
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    (Original post by jami74)
    Then with the rest of the acid, base and organic solvent I add dilute HCl into the separating funnel and shake. I removed the lower aqueous layer and placed into another separating funnel. (Now here I assumed that the base became protonated because of the HCl and so partitioned into the aqueous layer, is that correct?)
    Yep, the organic base has been protonated and falls into the polar aqueous layer :yep: The organic acid should have been unaffected by the acidification and should remain in the organic layer.

    This aqueous layer HCl solution is then neutralised with dilute NaOH, enough is added make it alkaline. More organic solvent is added and it is shaken and left to separate. The aqueous layer is removed and set to one side, the organic solvent layer is removed and analysed by tlc to show it contains acid.
    That's the part that I am confused about, can anyone explain it to me please?
    What should have happened here, is that the neutralisation with NaOH should have deprotonated the acid conjugate of the organic base you started with. Then extraction with an organic solvent should have resulted in recovery of the base...

    I don't know how/why you ended up with the acid instead based on what you've described :p: Are you sure the solution you were working on was the aqueous layer from the previous step? This is probably a yes since you ended up with a partition!
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    (Original post by EierVonSatan)
    Yep, the organic base has been protonated and falls into the polar aqueous layer :yep: The organic acid should have been unaffected by the acidification and should remain in the organic layer.


    What should have happened here, is that the neutralisation with NaOH should have deprotonated the acid conjugate of the organic base you started with. Then extraction with an organic solvent should have resulted in recovery of the base...

    I don't know how/why you ended up with the acid instead based on what you've described :p: Are you sure the solution you were working on was the aqueous layer from the previous step? This is probably a yes since you ended up with a partition!
    So what I think should have happened should have happened? Hmmm, the reason I am confused is because I got full marks for the lab and I clearly labelled the spot from that sample as being acid.

    Oops, meant to say: Thanks for replying
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    (Original post by jami74)
    So what I think should have happened should have happened? Hmmm, the reason I am confused is because I got full marks for the lab and I clearly labelled the spot from that sample as being acid.

    Oops, meant to say: Thanks for replying
    Did you have pure samples of the acid and base to tlc against to come to the conclusion that you ended up with acid?

    If you were still in the lab and got that result I'd suggest you tlc all of the solutions you had to try and find out what had happened since this isn't making a lot of sense...not that this would be the first time chemistry didn't play fairly :lol:
 
 
 
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