What am I doing wrong... "If a sample of pure benzoic acid, HC7H5O2, contains 3.96×1018 molecules, the sample

Question

I keep getting the answer "4.8360954e14" and it is wrong. I'm multiplying the weight of benzoic acid (122.12926) with 3.96e18 and then converting into mircograms (1e-6 micrograms=1 gram). am i doing all of this right?

the full question is: If a sample of pure benzoic acid, HC7H5O2, contains 3.96×1018 molecules, the sample contains _____ micrograms of benzoic acid.

I just tried that. i got 8.03375e-7. and it's wrong. please help.. again?

Answer 1

you have to multiply weight of benzoic acid by 3.96 x 10 (is that 1018 or 10^18?) and then devide by Avogadro's # to get the weight of Benzoic Acid in the sample in grams and then convert it to microgram.

Molar weight of BA = a
1mole of BA weighs a, that means:
6.0221415 × 10^23 molecules of BA weigh "a" grams, How much does 3.96 x 10^18 molecules of BA weighs in grams?

a x (3.96 x10^18)/(6.0221415 x 10^23) = weight of BA (in grams) in your sample.

Now you have to converts grams to micrograms.

Answer 2

Divide the number of molecules of BA first by Avogadro's number to get moles of BA. Then multiply by the molecular weight and then convert that number of grams to micrograms.

1 microgram = 10^-6 grams