How to deduce molecular formula from empirical formula?

Question

Solve this questions aswell:
An organic compound contains 12.8% carbon, 2.1% hydrogen and 85.1% bromine, by mass. Its relative molecular mass is 188.

a) Calculate its empirical formula.
b) Deduce its molecular formula
"plz show complete working as possible"

Answer 1

Molecular masses of relative atoms are : C - 12, H - 1, Br - 80
so the atoms are in quantity ratio 1:2:1 (no difficult maths there !)

Empirical formula is CH2Br which has an empirical mass of 94
so molecular formula must be twice this i.e. C2H4Br2 which is Dibromoethane

Answer 2

188 * .128 = Mass of total carbon atoms
188* .021 = Mass of total hydrogen atoms
188 * .851= Mass of total bromine atoms

take total mass of element over its molecular mass.... so for Carbon it would be 24 divided by 12 and that equals 2....so 2 C molecules...do the same for the rest. I believe this gives u molecular formula. For empirical formula just reduce the mol. formula down to the smallest common factor. I dont feel like doin the work 4 u cuz im lazy 2 lol......but im pretty sure this is how u do it. Good luck