First fine the formula weight for CaCO₃ by adding the atomic mass of each atom - Ca (40.078g) + C (12.0107g) + O * 3 (15.9994g * 3) = 100.0869g
Take the mass of each individual atom type, divide by the overall mass (100.0869g) and multiply by 100 to find the percent composition of each atom type.
(40.078g)/(100.0869g) * 100 = 40.042%
(12.0107g)/(100.0869g) * 100 = 12.0003%
(15.9994g * 3)/(100.0869g) * 100 = 47.9565%
