Question

Molecular Formula Question: Vanillin is the compound containing carbon, hydrogen, and oxygen that gives vanilla beans their distinctive flavor. The combustion of 30.4 mg of vanillin produces 70.4 mg of CO2 and 14.4 mg of H2O. The mass spectrum of vanillin shows a molecular-ion peak at 152 amu. Use this information to determine the molecular formula of vanillin.

Answer 1

.0704 g CO2 --> 27.3% C, 72.7% O --> .0512 g O, .0192 g C --> .0032 mol O, .0016 mol C

.0144 g H2O --> 11.2% H, 88.8% O --> .0128 g O, .0016 g H --> .0008 mol O, .0016 mol H

so, in the .0304 g of vanillin, there are 0.004 mol O, 0.0016 mol C, and 0.0016 mol H.
The empirical formula is therefore H2C2O5.
This would have a molecular mass of 106.4 amu.
I'm not sure how this will work out, since 106.4 doesn't divide evenly into 152. Then again, I didn't really learn about the mass spectrum or molecular-ion peaks. Can you do it from here?