All you need to get the molecular weight is a periodic table. Take the number of each atom present in the molecule and multiply it by the atomic mass of the atom, which is listed on the periodic table, then add them all up. For example, methane, CH4: 12.011 + 4*1.0079 = 16.0426.
The short cut would be to figure out the percentage of the mass that is hydrogen and then multiply that percentage by the total mass that you have. You would be doing essentially the same thing with the molar conversion, but it's more stepwise.