Tetrodotoxin is a toxic chemical found in the fugu puffer fish, a popular but ra

Question

Tetrodotoxin is a toxic chemical found in the fugu puffer fish, a popular but rare delicacy in Japan. This compound has an LD50 (the amount of substance that is lethal to 50% of the population) of 1×10 1ug per kg of body mass. Tetrodotoxin is 41.38% C, 13.16% N, and 5.37% H, with the remaining amount consisting of oxygen.

a. what is the empirical formula of tetrodotoxin?

b. using the mass spectrometer, the molecular mass of the tetrodotoxin was measured as 320.0g/mol. what is the molecular formula of this compound?

c. what is the weight, in grams, of a LD50 dosage of tetrodotoxin for a person weighing 165 pounds?

Explanation / Answer

A. To find the empirical formula:
take the percentages of each and convert them to grams. then divide by molar mass
41.38 g C / 12.01 g/mol = 3.45 mol C
13.16 g N / 14.01 g/mol = 0.939 mol N
5.37 g H / 1.01 g/mol = 5.32 mol H
40.09 g O / 16 g/mol = 2.51 mol O
now divide each element by the one with the least moles
3.45 mol C/ 0.939 = 3.67
0.939 mol N / 0.939 = 1
5.32 mol H / 0.939 = 5.66
2.51 mol O/0.939 = 2.67
since these aren't whole numbers you must multiply by the common denominator, which in this case is 3
C = 11
N = 3
H = 17
O = 8
the empirical formula is C11N3H17O8

B. The molar mass is 319.31 g/ mol
since this number is equal to molecular mass measured as 320.0g/mol, the empirical formula is the same as the molecular formula .

C.You'd need 1650 micrograms of the compound
= 1.65 * 10-3 grams

1.65 * 10-3 / (319.31 g/mol) * (6.022 *1023 molecules / mol) =

3.11 * 1018 molecules.

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