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Empirical Formula For Tetrodotoxin

  1. Oct 14, 2013 #1
    1. The Question: The pufferfish is an Asian delicacy, but also contains a deadly toxin, tetrodotoxin. The LD50 (lethal dose to kill 50% of the population) is 10 micrograms/kg. An analysis of 18.34 mg of tetrodoxin produced 27.82 mg of carbon dioxide, 13.2 mg of nitrogen dioxide, and 8.83 mg water in a combustion reaction.

    a) Determine the empirical formula for tetrodotoxin. b) What mass of tetrodotoxin is the LD50 for a 70kg person?


    2. The answer is C11H17N3O8, but I'm not getting it.

    After converting to mass, and then back to moles, then dividing by the smallest # of moles, and then multiplying by the factor ("common denominator") that gives all integer values....I'm not getting what I'm supposed to be getting. I've also checked 5 times to make sure I'm not punching something wrong in the calculator.


    3. I'm not gonna type out the WHOLE thing of how I arrived to my answer, cause it took about one page of writing to arrive at the answer. But I'm not getting C11H17N3O8 for the empirical formula, I keep getting C11H17N5O6 which is WRONG. Not sure what I'm doing wrong, but if someone could help me, that would be great. Thanks! (I've attempted this question 5-6 times already, and keep getting the same WRONG answer.)
     
  2. jcsd
  3. Oct 14, 2013 #2

    SteamKing

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    You could show the reaction which results from the combustion of TD. There may be a mistake there. If you don't show something, you can't expect help.
     
  4. Oct 14, 2013 #3

    DrDu

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    Your calculation seems to be right. Maybe your teacher misread a 5 for a 3 when setting up the exercise.
     
  5. Oct 14, 2013 #4

    Borek

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    I got N5 as well.
     
  6. Oct 17, 2013 #5
    Thanks everyone. It turns out that the teacher made an error in 1 of the masses. So the empirical formula (re-calculated) IS still C11H17N3O8. But now I'm stuck on Part b. I calculated the molar mass of tetrodotoxin which is 319g/mol. Does Avogradro's # play a role here in the calculation? I'm clueless again.
     
  7. Oct 17, 2013 #6

    SteamKing

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    There's 1 Avogadro's number of molecules in a mole, if that's what you are asking. That works for any substance.

    For part b, you are given the LD50 dosage (10 micrograms/kg body weight) How much toxin is required for the LD50 dosage if a person has a mass of 70 kg (This can be solved by looking at the units)
     
  8. Oct 17, 2013 #7
    700 micrograms? I don't know....
     
  9. Oct 17, 2013 #8

    SteamKing

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    Fine. Give him a whole gram. He'll be deader than last week's news.

    The point about deadly toxins is, it doesn't take a whole lot of it to kill someone.
     
  10. Oct 17, 2013 #9

    Borek

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    700 μg it is.
     
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