Question

A compound contains 64.27% carbon, 7.19% hydrogen, and 28.54% oxygen. the molar mass is 168.19 g/mol. what is the molecular formula

Answer 1

Empirical formula is the simplest ratio of whole numbers of components in a compound 
calculating for 100 g of compound 
                                             C                             H                             O
mass                                  64.27 g                   7.19 g                     28.54 g
number of moles        64.27 g / 12 g/mol      7.19 g/1 g/mol     28.54 g / 16 g/mol 
                                        = 5.356 mol           = 7.19 mol           = 1.784 mol 
divide by least number of moles  
                                     5.356 / 1.784            7.19 / 1.784         1.784 / 1.784
                                      = 3.002                     4.03                     = 1.000
rounded off to nearest whole number 
 C - 3
 H - 4
 O - 1
empirical formula - C₃H₄O
 
 mass of empirical formula = 12 g/mol  x 3 + 1 g/mol x 4 + 16 g/mol x 1 = 56 g
molecular mass = 168.19 g/mol 
molecular formula is the actual ratio of elements making up the compound 
number of empirical units = molar mass of molecule / empirical mass
      empirical units = 168.19 g/mol  / 56 g = 3.00
there are 3 empirical units making up the molecular formula 
molecular formula = 3 x C₃H₄O

molecular formula = C₉H₁₂O₃