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PET depolymerization

  1. Feb 5, 2012 #1
    1. The problem statement, all variables and given/known data

    Hi, I recently did a lab where PET plastic was depolymerized into terephthalic acid and ethylene glycol. I was wondering how to figure out the moles of terephthalic acid (in mol) that was reacted. I'm not really sure how to calculate this since terephthalic acid isn't a reactant itself and is just mostly present in the form of a copolymer.
    PET reacted = 2.482g or 0.01291605 mol
    Mass of the copolymer unit = 192.164 g/mol
    Mass of terephthalic acid = 166.128 g/mol
    Mass of ethylene glycol = 62.068 g/mol

    3. The attempt at a solution
    If terephathalic acid was a reactant I would think it would mean that since 0.01291605 mol of PET reacted, 0.01291605 mol of terephathalic acid reacted, but don't know if this is correct.

    Thanks!
     
  2. jcsd
  3. Feb 6, 2012 #2

    Borek

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    Staff: Mentor

    You are doing some strange things. How do you know number of moles of PET? And what do you mean by "acid that reacted" - acid that was produced?
     
  4. Feb 6, 2012 #3
    In the experiment we used 3g of PET plastic and after it had been in the reflux condenser I weighed out how much PET plastic hadn't reacted, which when subtracted from the 3g, gave me the mass (2.482g). I converted that into the amount of moles of PET that reacted with this equation : (1 mol PET copolymer unit/192.164g)*2.482g = 0.01291605 mol.

    What's meant about the amount of acid reacted is the theoretical yield as I need to do % yield calculations. It's definitely not the amount of acid produced though, as that was weighed out at the end.
     
  5. Feb 6, 2012 #4

    Borek

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    Staff: Mentor

    So when you state "moles of PET" you really mean "moles of copolymer unit". That's not exactly how a mole is understood in polymer chemistry.

    But I agree - seems like 1 mole of acid is produced per 1 mole of copolymer units.
     
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