Question

What is the empirical formula of a compound that is 66.6% c, 11.2% h, and 22.2% o by mass?

Answer 1

The empirical formula of a compound is the simplest ratio of components making up the compound.
In 100 g of compound,there's 66.6 g of C, 11.2 g of H and 22.2 g of O
lets calculate for 100 g of compound 
                              C                                 H                             O
mass                     66.6 g                         11.2 g                      22.2 g
number of moles   66.6/12 g/mol           11.2/1 g/mol              22.2/ 16 g/mol
                               = 5.55 mol                =11.2 mol                 =1.3875 mol
 divide by the least number of moles 
                               5.55/1.3875              11.2/1.3875             1.3875/1.3875
                               = 4                             = 8.08                     = 1
round them off to the nearest whole number 
C - 4
H - 8
O - 1
Therefore empirical formula of compound is C₄H₈O