[kcchan128]

Hi,

I have done an experiment about the extraction of adipic acid in ethyl acetate to calculate the distribution coefficient, KD, after first and second extractions. We took the KD in the ratio of Ether:Water.

There's 3 parts,
First part,
is just the 1% aqueous solution of adipic acid, titrate it with NaOH

Second part, (only 1 extraction)
Ethyl acetate was added to the adipic acid. Separate the aqueous layer and titrate it with NaOH.

Third part, (2 extractions)
Ethyl acetate was added to the acid twice. Repeat the titration steps.

Based on what I understand from this experiment is that when the ethyl acetate is added to the Adipic acid,
some of the adipic acids are  extracted with the ethyl acetate(move to the organic layer) and some are remain in the water.
As more extractions being carried out, it should be less adipic acid remains in the water.
This would make KD value getting larger.

Is that the right way to look at the problems?

We were asked to calculate the concentration and the millimoles of adipic acid in ethyl acetate layer and in aqueous layer after 1 extraction and after 2 extractions. All these values should be used to calculate the KD.
Using the concentration value, we should be able to calculate KD, but why they want us to calculate the millimoles as well?

Thanks

[matt314]

From what I understand, the Kd represents the ration of the concentration of acid in the aqueous layer vs the concentration of acid in the organic layer. If you do one extraction you simply calculate by taking the the concentration of acid in the water (obtained from the titration) and the concentration of the acid in the organic phase (found by doing the original amount of acid in water found in the first part of the experiment minus the amount in the new aqueous phase).

If you do two extractions you need to find the amount in the second organic phase (Amount in original aq. phase minus amount in new aq phase minus amount in organic phase after 1 extraction) and the second aqueous phase to do the ratio. This ratio should theoretically be the same since you are simply calculating the fraction of the amount that went to the organic phase vs. the amount that went to the aq phase.

I assume you simple calculate mmol to give you practice or to make you results more complete. They could be used to calculate Kd using (W1/V1) / (W2/V2) but you can just use the C1/C2 formula.

P.S Your a uOttawa student aren't you :p I had to dig through my old labs to find you answer!

[vittoria]

Hi,

I am also an Ottawa U student, and have the same lab report to work on
Thanks, matt314, your answer has helped me. I have other questions, though, if anyone could help me it would really be appreciated!

I've been asked to find the number of millimoles of adipic acid in ethyl acetate after 2 extractions and the number of millimoles of adipic acid in the organic phase after 2 extractions. Shouldn't the values of both these answers be identical, since (if I'm not mistaken) ethyl acetate is the organic phase anyway? I have no idea of how to calculate this  I used your answer to find the number of millimols of acid in organic phase, yes, but during the second extraction. Should I have not done this, did I confuse data?

Also, correct me if I'm wrong, but if I find the concentration of adipic acid in the organic phase, I can multiply it by the volume of the organic phase obtained to cancel the litre units, then convert it into millimoles?

Finally (I'm sorry if this is a long post), to find the total number of millimoles of acid extracted by both extractions with ethyl acetate, would adding the number of millimoles in organic phase after the first extraction with the number of millimoles obtained in the organic phase during the second extraction do the trick? Or should it be with the number of millimoles of acid in organic phase AFTER the second extraction?

Thanks ahead!
P.S. I bolded certain words because what T.A.'s ask is very similar and varies only by one word.