Converting compound from mass (g) to # of atoms

Question

Convert 0.20 grams of CaCO3 to number of atoms.

: (molar mass is 100.09 g CaCO3)

Which is correct? # 1 or # 2?

Method # 1

0.20 g CaCO3 x 1 mol CaCO3 / 100.09 g CaCO3 x

6.02 x 10^23 molecules CaCO3 / 1 mol CaCO3 x

5 atoms / 1 molecules CaCO3

ans: 6.01x10^25 atoms of CaCO3

Or Method # 2:

I seen 1 mole = 6.02x10^23 atoms, so others will convert from grams to moles, then to atoms.

(not sure if this only apply to single element only?)

0.20 g CaCO3 x 1 mol CaCO3 / 100.09 g CaCO3 x

6.02 x 10^23 atoms CaCO3 / 1mol CaCO3

ans: 1.02 x 10^25 atoms of CaCO3

Thank you!

Answer 1

Hello Liz,

The first method is correct because you only have one mole of CaCO3. If you multiply it by 5 at the end that would give you the amount of atoms in 5 mols of CaCo3.