Question

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?

Answer 1

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

Answer 2

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.