Empirical Formula For Tetrodotoxin

[Astronomer1]

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 going to 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.)

 

[SteamKing]

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.

 

[DrDu]

Your calculation seems to be right. Maybe your teacher misread a 5 for a 3 when setting up the exercise.

 

[Borek]

I got N₅ as well.

 

[Astronomer1]

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.

 

[SteamKing]

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)

 

[Astronomer1]

700 micrograms? I don't know...

 

[SteamKing]

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.

 

[Borek]

700 μg it is.