Determining Empirical and Molecular Formulas

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Kate_Santoso_4F
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Determining Empirical and Molecular Formulas

Postby Kate_Santoso_4F » Mon Oct 08, 2018 9:39 pm

We are asked to solve for the empirical or molecular formula of a more complex compound such as caffeine and given the molar mass and the amounts of each of its atoms in grams. After we finally solve for the molar ratios of each of the atoms for caffeine, how do we know what order in which the atoms go in the final molecular formula?

yea-lyn pak_1G
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Joined: Fri Sep 28, 2018 12:18 am

Re: Determining Empirical and Molecular Formulas

Postby yea-lyn pak_1G » Mon Oct 08, 2018 10:33 pm

Not a hundred percent sure on this, but I think the general rule is that carbon is first, followed by hydrogen, and everything else remaining is placed alphabetically afterwards. So for example, if you have carbon, nitrogen, hydrogen, and oxygen, it would be: CHNO.
I don't know if points are taken off for placing the atoms in an incorrect order, though.

Hope this helps!

Matthew Mar 1J
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Re: Determining Empirical and Molecular Formulas

Postby Matthew Mar 1J » Thu Oct 11, 2018 3:21 pm

I think that's the right ordering most of the time, but you have to be careful with ionic compounds since there could be polyatomic ions which don't always follow that kind of ordering (e.g. things like sulfates (SO4) where the oxygen goes at the end or hydroxide (OH) with oxygen before hydrogen).


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