How can you find the molecular formula of a compound when its percentage composition is given?

Answer 1

Yes, if you have some additional information, such as the molecular weight. For instance, the molecules C2H4 and C4H8 have exactly the same percent composition, but they are very different molecules. So you need some other information to tell them apart than the percent composition.

Answer Expanded

This is kind of a trick question. By knowing the percent composition, you would easily be able to determine its empirical formula, but molecular formula is a bit different. The molecular formula is the actual number of atoms in a molecule, so in order to find the specific molecular formula of a substance, you would also need to know how many grams there is of that substance.

(This explains the difference between C2H4 and C4H8)

Answer 2

From the percentage composition only, an empirical formula can be derived, but a proper molecular formula can only be assured by adding some information about the molecular weight of the substance concerned.

Answer 3

You have to find its empirical formula using the percentage composition. When you have done that, work out the relative molecular mass (Mr) of the empirical formula. This should be a multiple of the compound's Mr, so you multiply the amount of each atom in the empirical formula by this number, which gives you the final molecular formula.

Answer 4

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