Molecular Formula

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Step 2

The second step can be the trickiest and most involved step, or the easiest and fastest step. The question will either give you the masses (usually in grams) of each of the elements in the substance (easiest!), or it will give the masses (usually in grams) of the products (hardest!). If you encounter the second, you will have to find the mass percentages of each product, and plug in the totals to the unknown substance. Because the first scenario requires no mathematical work, and example of the second scenario will be given.

Continuing the example!

<example still pending>

What is molecular formula? Molecular formula is very similar to EmpiricalFormula. However, the molecular formula of a substance is the exact chemical composition, while the empirical formula is the simplified formula. For example, the chemical formula of glucose is C₆H₁₂O₆, but the EmpiricalFormula is CH₂O. 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 either of the correct formulas? 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.
Here`s an example!
<example pending>

Step 2

The second step can be the trickiest and most involved step, or the easiest and fastest step. The question will either give you the masses (usually in grams) of each of the elements in the substance (easiest!), or it will give the masses (usually in grams) of the products (hardest!). If you encounter the second, you will have to find the mass percentages of each product, and plug in the totals to the unknown substance. Because the first scenario requires no mathematical work, and example of the second scenario will be given.
Continuing the example!
<example still pending>