What is the mass in grams of 6.5*10^20 molecules of aspirin (C9H8O4) ?

We have a couple of steps to do:

1. Figure out the number of moles of Aspirin using Avogadro's Number

2. find the molar mass of Aspirin

3. Calculate the mass in grams

[1]. 6.5 x 10^20 molecules x (1 mole / 6.022 x 10^23 molecules) = 1.08 x 10^-3 moles Aspirin

[2]. Using the atomic masses from the periodic table for each element C, H, and O, find the molar mass of Aspirin (9 x 12.011) + (8 x 1.008) + (4 x 15.999) = 108.099+8.064+63.996 = 180.159 grams/mole

[3]. multiply to find the answer:

1.08 x 10^-3 moles x (180.159 grams/mole) = 0.195 grams (moles cancel out)

Since the given answer only has two significant figures, the answer should only express in 2 sig figs, too:

2.0 x 10^-1 grams Aspirin