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What is molecular formula? The molecular formula of a substance is the exact chemical composition. For example, sucrose is C12H22O11. But given only a combustion reaction for a substance containing only carbon, hydrogen, and oxygen, and given the masses of the products, how could one arrive at the correct formula? Below are the neccessary steps in finding molecular formula. If you ever get stumped, just remember the golden rule: stoichiometry!
Finding Molecular Formula
Step 1
What is in your substance? You will most likely be given either A) a chemical analysis and the mass percents of each, or B) a combustion reaction and the masses of the products. From this information, you can compile a list of all the elements in your substance.
The first is the easiest, as it is only working with percentages and ratios. The latter involves a good amount of thinking and a lot of stoichiometry. However, both are rather easy to do, once you know what is going on.