# chemisty help

• Nov 12th 2012, 04:09 PM
Louisana1
chemisty help
An unknown acid has a molar mass of 60.05 g/mol. Given the following percent composition, what is the molecular formula? 40% C, 6.7% H, 53.3% O

please show me how to work this out
• Nov 12th 2012, 05:00 PM
HallsofIvy
Re: chemisty help
Look up the atomic weights of C, H, and O. If the molecule has n C atoms, m H atoms, and p Oa atoms, then the molecular weight would be nC+ mH+ pO where "C", "H", and "O" are now the atomic weights of those atoms.
• Nov 18th 2012, 06:09 PM
divans
Re: chemisty help
The unknown acid has a mass of 60.05 grams. You need to know the atomic weights of C (12.01) H (1.01) and O (16.00). You know that the molecular formula is 40% Carbon (the percent composition) so multiply 60.05 with .400 (the mass of the acid and the decimal representation of the composition of carbon) and you get 24.02. What this tells you is 24.02 grams of the 60.05 grams are Carbon. In order to find the number of carbon atoms in the acid you have to divide this number with the atomic mass of carbon, and you get 2. So the molecular formula will be C2HxOy, you still need to find x and y. You can find them with a similar method.