chemistry
posted by jaz .
Determining a Molecular Formula from an Empirical Formula
1. A compund has an experimental molar mass of 78g/mol. Its empirical formula is CH. What is its molecular formula?

The idea here is to see how many CH groups you have or put another way (CH)_{x} where you want to determine x.
So if x is 1, what would the molar mass be? It would be 12 for C + 1 for H = 13 for the CH. If x = 2, then the molar mass would be 26. If x = 3, the molar mass would be 3 x 13 = 39. So what time 13 = 78 (or close to it). 
13 times 6 =78

CH=78g/mol
but the relative atomic mass of C=12 and H=1
therefore the molecular mass would be
(12+1)n=78 g/mol
13n = 78 g/mol
n=6
the molecular formula is C6H6 .