The empirical formula of styrene is ch; its molar mass is 104.1 g/mol. what is the molecular formula of styrene?

a) c2h4
b) c8h8
c) c10h12
d) c6h6
e) none of these

i got c8h8 because i did
mwef=n

but it says the answer should be c2h4

how is that possible?

You got the answer correct. If you would double check
given:C (12 g/mol) H (1 g/mol). 

12(8) + 1(8) = 104 g/mol

and for C2H4
12(2)+1(4) = 28g/mol

Also, chemical formula of styrene is C6H5CH=CH2.

1. Find the molecular formula of styrene 

Molecular formula = n x empirical formula 

n= 104.14/13.02 = 8 where 13.02 is the empirical mass of CH 

Molecular formula = CH x 8 
= C8H8 

2. From step 1, one molecule of styrene contains 8 atoms of hydrogen or one mole of styrene molecules contains 8 moles of hydrogen atoms (remember the formula of styrene is C8H8). 

3. Convert 3.49 g styrene to mole styrene 

mole styrene = 3.49 g/104.14 g/mol = 4.71 x 10^-3 mole 

4. Calculate mole of hydrogens equivalent to 4.71 x 10^-3 mole styrene. Use mole ratio from step 2. 

mole H = 4.71 x 10^-3 mole styrene * 8 moles H/1 mole styrene 

mole H = 0.0377 mole 

5. Find number of H atoms contained in 0.0377 mole of hydrogen atoms. Use Avogadro's number. 

no. of H atoms = 0.0377 mole H * 6.02 x 10^23 atoms H/1mole H 

no. of H atoms = 2.27 x 10^22 atoms H