Determining Empirical formula

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Madelyn Cearlock
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Determining Empirical formula

Postby Madelyn Cearlock » Mon Nov 19, 2018 1:27 pm

Can someone help me start the problem of finding the empirical formula when given molecules instead of atoms. For example, the question asks to find the empirical formula given 1.811 g of CO2 and 0.3172 g of H2O. Thank you!

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Re: Determining Empirical formula

Postby Chem_Mod » Mon Nov 19, 2018 3:07 pm

You must figure out how much Carbon, Hydrogen, and oxygen you have in your original sample using principles of conservation of mass. See UA, TA office hours for detailed help.

Justin Haggard 1E
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Re: Determining Empirical formula

Postby Justin Haggard 1E » Thu Nov 29, 2018 10:50 pm

You would need to find the moles of the entire molecules first, then use mole-to-mole ratios to find the moles of each element.

Start with the molecule:

of moles of

Now calculate moles of Carbon and Oxygen from the moles of :

moles of of Carbon

moles of of Oxygen

Then you would do the same for the molecule, then add the moles of Oxygen together (from the and molecules) to get the total moles of Oxygen.

Then divide all of the moles of the elements by the smallest value to get whole number ratios, which would give you the empirical formula.

Hope this helps.

Jasmine Chow 1F
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Re: Determining Empirical formula

Postby Jasmine Chow 1F » Wed Dec 05, 2018 12:26 pm

You should first convert all your elements into moles. you then divide by the smallest mole value to get your empirical equation values. Last multiply if needed to get whole numbers.

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Re: Determining Empirical formula

Postby uhedlund » Sun Dec 09, 2018 10:16 am

First, you must convert the molecules to moles. Using molar ratios, you can find grams of each of the individual elements. Then convert the masses of the individual elements to moles, and proceed to divide by the smallest number of moles (ex: if H=2, O=4, and H=6 divide all by 2) to find Empirical formula.

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