how do i work out the molecular formulae of a compound when ive been given the mass of each element as a %?

Question

I know how to work out the emperical formulae, but how do I get the exact amount of atoms for each element (molecular formulae)

Thanks

Answer 1

I'm also depending on memory, but if you can calculate the relative amounts of each atom in a molecule you still need to know how these atoms are arranged to get the molecular formula. Molecules made up of the same atoms but with different structures are isomers.

Answer 2

OK - I'm making this up a bit from memory and I expect you will get a recent student or teacher confirming or telling me it is rubbish......

Divide the percentage number for each element by the atomic weight of that element (e.g. if carbon is 36 percent you get 36/12 = 3). Take the smallest number and divide it into all the others so you have a ratio of atoms of each element in the molecule. It wouldn't help you know the difference between C2H6 and C4H12 but you would get the ratios right.

Answer 3

You did the hard part if you can get the empirical formula from the mass percentages. To get the molecular formula, you need to know the molecular weight.

Answer 4

xy2(x=y2xx2-y3)