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Help with my unknown in the second organic chemistry

  1. Oct 17, 2012 #1
    1. The problem statement, all variables and given/known data
    Okay, I just started working on my unknown in Lab and I got stuck with a liquid. First I determined the boiling point, my professor told me to let this step go for 30 minutes and it plateaued at around 147°C. I did this twice the first time I didn't do it as long and got a 140°C reading. Then I did the solubility test in water and found that 3mg of unknown to 1mL of H20(distilled) and it dissolved so it was soluble in water. Is this really uncommon for an unknown to dissolve in water or did i mess up somewhere? I then performed litmus test. Should I be worried.



    2. Relevant equations
    The text book. Not applicable




    3. The attempt at a solution
    I did the solubility test twice. Also performed litmus test twice. The litmus test gave me a neutral reading.
     
  2. jcsd
  3. Oct 18, 2012 #2

    Borek

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    Staff: Mentor

    It is not clear to me what kind of help do you expect. So far you are just collecting data, you don't know enough yet to tell anything.
     
  4. Oct 18, 2012 #3
    Thanks. I was just worried and freaking out that I did something wrong.
     
  5. Oct 18, 2012 #4

    Borek

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    I am not saying you didn't. 3 mg in 1 mL of solvent look rather strange to me, I would expect more like 30 mg per 1mL. But I have no idea what is the procedure you are expected to follow, so whatever I think doesn't matter much at this stage.
     
  6. Oct 18, 2012 #5
    Oooops you're right.lol. That's what i meant. I read the scale at 0.036g. And then at 0.041g. It felt like I hardly put anything in there.
     
  7. Oct 23, 2012 #6
    Hey Borek, thanks for helping. I turned my preliminary in and was right. So it is either a (low MW neutral alkene, alkyne, alchohol, ketone, amide, nitro compound, aldehyde, ester, ether). I have another question though, my professor told me to proof check my boiling point and put a no by it. This is how I determined it: I placed a thermometer about 1 cm above 0.5 mL of the liquid unknown in a test tube. I slowly heated the liquid to boiling. And allowed it to keep going for 30 minutes and obtained my max value and gave it a range of + or - 5 degrees Celsius. I'm confused because this what he told us to do. I thought the boiling point was as soon as it started to bubble, so is he wrong. Or am i just doing something wrong?
     
  8. Oct 23, 2012 #7

    Borek

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    You have boiled the liquid for half an hour without condenser, and it didn't run away? Either I don't understand what you wrote or there is something missing from your description, or you are using approach that I have never heard of.
     
  9. Oct 24, 2012 #8

    chemisttree

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    It's best to determine boiling point above the surface of the liquid just beneath the point where
    condensation occurs.
     
  10. Nov 14, 2012 #9
    Thanks guys, the boiling point was 155°C-165°C which has given me a choice of 6 possible compounds. List compound with respective boiling point in (°C): (+-)-4-Heptanol 156, 1-hexanol 159, cyclohexanol 160, (+-)-2-Heptanol 160, 3-chloro-1-propanol 161, (+-)-cis-2-methylcyclohexanol 165. These have 5 possible derivative we can make. I can only make three due to lack of chemicals in lab(we're poor). Phenylurethane, 4-nitrobenzoate, and 3,5-dinitrobenzoate. My phenylurethane derivative i feel was a disaster because it yield very little product and started to melt at 77, but didn't finish at all, even at 160°C. So i'm guessing that's really impure, which i still don't understand why the melting point is that high for it. The 77°C responds to my 82°C melting point of phenylurethane for cyclohexane. My next derivative 3,5-dinitrobenzoate melted at 103-105°C which i thought was good. This left only one choice because only one of my 6 choice had a melting point higher than that which is the cyclohexanol at 113°C. I tried making the 4-nitrobenzoate derivative today with no result(no filtrate) just went straight through vacuum filtration. I'm going to an extra lab tomorrow for another go at it. From my result do you think it's cyclohexanol or not enough information given. We don't get spectra until we figure out what our unknown is.

    p.s Just to clarify, if my compound melting at 103°c the secret compound can only be higher than that melting point. Is that a good rule of thumb.

    Thank you,
    you guys are amazing
     
  11. Nov 14, 2012 #10
    And my solubility test said it was a low MW and neutral too...
     
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