Question

How many hydrogen atoms in a baby aspirin tablet which has 81mg of aspirin? (aspirin is C9H804)

Answer 1

allisante r u in chemistry 1st semester?

Answer 2

yes i am

Answer 3

i started with 81mg aspirin, divided by 1000mg to get grams, then divided by 180.154 grams (the molar mass of aspirin), then multiplied by 8 moles of hydrogen, then multiplied by avogadros number. Im not sure if that is correct though...

Answer 4

allisante

Answer 5

i think the answer is 14590.943505

Answer 6

yep. it's correct.

Answer 7

samsterz, how did you get the answer though?
aaronq, which answer is correct?

Answer 8

how did i get the correct answer? did some math

Answer 9

well thats the whole problem im having. i dont want someone to just hand me the answer. i want to KNOW how to do it so that i can do it myself too. i need to figure out how to set up the equation.

Answer 10

Grab your periodic table and look up the amu for each element.
Add together the weights per mole, for example, the amu for Carbon (C) is 12.011g/mol
\[9(C) + 8(H) + 4(O) = total\frac{g}{mol}\]
convert mg to g to mol to atoms
\[81mg \times \frac{g}{1000mg} \times \frac{mol}{total g} \times \frac{6.022\times10^{23}atoms}{mol}\]

Answer 11

Thank you! so, for the mol/totalg part, i write 8mol/180.154g?

Answer 12

\[9C+8H+4O\]\[9(12.011\frac{g}{mol}) + 8(1.008\frac{g}{mol}) + 4(15.999\frac{g}{mol})\]\[=18.159\frac{g}{mol}\]We're saying here that 18.159g of our molecule is the same mass as 1 mole of our molecule so we can also say\[\frac{1 mol}{18.159g}\]

Answer 13

Here it is in full blown scientific notation, just for practice
\[8.1\times10^{1}mg\times\frac{g}{10^{3}mg}\times\frac{mol}{1.80159\times10^{2}}\times\frac{6.022\times10^{23}atoms}{mol}\]\[8.1\times6.022\div1.80159\]\[=27.075=2.7\times10^{1}\]add up the exponents
\[10^{1+1-3-2+23}=10^{20}\]therefore you have\[2.7\times10^{20}atoms\]to two significant figures because you have two sig.fig. in 81mg

Answer 14

thank you!