[r4bbit_]

lol my time is running out 
I did some more reading on that site, it seems like most of the carbonyl reactions require an acid catalysts though.

[azmanam]

If you're in a time crunch, I'm going to humbly suggest you submit your best guess and explain why your acid is essentially un-determinable given the data you have and the limitations therein.  We just needed more data.

Most carbonyl reactions can be run catalytic in acid or base, usually to give the same result (but not always).

After you turn it in and perhaps discuss with your instructor, come back and I'll give you more suggestive hints (like results of tests you couldn't run) and we'll get to the answer, I promise.

Make sure you talk about what you've learned here.  What experiments you can run next time to help with analysis.  Which tests gave poor results and why.  imho (and I'm not grading you) I think the critical thinking skills you've worked through here are much more valuable than guessing the right acid.  You may not get full credit (b/c you may not guess the technical correct answer) but knowing why it's better than wildly guessing and happening to guess correctly.

[Borek]

You know the compound is a monoprotic acid.

Could be I am missing something, but so far I have not seen any proof. Titration curve shape is not decisive.

[azmanam]

I suppose that's true.  We did have to throw everything else out from that experiment, didn't we.

[Arkcon]

You know the compound is a monoprotic acid.

Could be I am missing something, but so far I have not seen any proof. Titration curve shape is not decisive.

This may well be the biggest problem with this analysis.  I've seen the three plateau curve in textbooks too, but like Borek showed, when you try to do them in real life, you may not get the curve, I know I didn't for a diprotic amino acid in my analytical chemistry class.  The big problem is that it colors all our other perceptions about the other analyses.

[r4bbit_]

Yay, finished it!!! I still couldn't get what you were talking about, but for mine I said that not enough analyses could be conducted, and ...
I mentioned 2 cases:

case 1 - pka value wrong, acid in fact diprotic, hence making malic acid the unknown acid.

case 2 - 2 reactions goin on at the same time, likely to be a halogen group or a carbonyl group that reacts with NaOH at the side ( although i couldn't figure why).

And thanks to Borek for the citric acid example, it worked nicely in my explanation for case 1. Thanks for all your help, I made sure i included all of the things we've discussed and I also listed some tests that should be conducted to see presence of carbonyl (Fehling's test or Tollen's reagent etc).

If you have time before next Wednesday to tell me what your guess was, please do so, I would be glad to hear it  . My instructor is going to tell me my acid about next wednesday when he marks it.

[azmanam]

Maleic acid wasn't my guess, but I can't be totally for sure my guess was right

Here was my thought process:  NaOH acted as a base to remove the proton from your (in my guess) monoprotic acid.  It also acted as a nucleophile and saponified an ester (the second carbonyl) you have in your acid.  This created acetic acid as a byproduct, which could then continue to be titrated to a phenolphthalein endpoint.

This acid also reacts with 2 moles of ethanol in acid to produce the ethyl ester of the original carboxylic acid and ethyl acetate (in the same mechanism as the saponification, but this time it's a trans-esterification).  This is the origin of your nail polish remover smell.

Your guess has mp = 138, bp = 135 (decomp).  My guess has mp = 138-140, bp = 140 - so that's a wash.

Another test I would have run is a bromine test for alkenes - maleic acid would yield a positive result, my guess would have failed a bromine test.

Both of our guesses would fail a Jones test.

Both of our guesses would fail a Tollens test, as well as Fehling's test

Your compound would pass a KMnO4 test, mine would not.

Both of ours would fail an ferric chloride test (but if you retested my guess AFTER the phenolphthalein titration, it would give a positive result!)

Both of our guesses would fail a 2,4-DNP test.

[Borek]

The problem was giving me a headache - till I found what azmanam mean

[azmanam]

I was wondering who'd catch on first

[Borek]

I have browsed melting points table about 8 hours ago

[r4bbit_]

Saponification? I have never learned about it  My instructor never taught us =(
Is it possible that someone can perhaps include an electron transfer diagram of the mechanism?
I read briefly on wikipedia but the mechanism seems pretty crude.

[azmanam]

Start here:

http://www.cem.msu.edu/~reusch/VirtTxtJml/crbacid2.htm#react1
http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch20/ch20-3-3-1.html

If you're interested haystacks, (my guess of) your compound is buried within the MSU page - but not in the section I linked to.

[r4bbit_]

=( couldn't find it. Tell me IUPAC  .
But somehow, I feel it's an ester, because from what you said, if it saponifies, then sounds awfully like an ester.