Question

Now if your lab partner determined that there were 1.552 x 1022 atoms of H in an unknown sample of C2H4Cl2, how many milligrams would the unknown sample weigh? 
There was 0.56 moles of H from the first question. 

Answer 1

To determine the mass of the sample in milligrams in this problem, we use the avogadro's number to convert from atoms to moles, relate the moles of element in the sample to the mole present and the molar mass of the sample. We do as follows:

1.552 x 10^22 atoms H ( 1 mol H / 6.022x10^23 atoms H ) ( 1 mol C2H4Cl2 / 4 mol H ) ( 98.96 g C2H4Cl2 / 1 mol C2H4Cl2 ) = 0.625 g C2H4Cl2 = 625 mg C2H4Cl2