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April 24, 2014

Homework Help: Chemistry

Posted by Justyna on Wednesday, October 18, 2006 at 5:06pm.

what is the molecular formula of a compound that is 54.5% C, 9.09% H, and 36.4% O. with a molecular weight of 176g/mol.

A)C8H16O4
B)C4H8O2
C)C7H12O5
D)C9H18O3


Assume you have 100 g of the substance, then you have 54.5g of C, etc.

Moles C= 54.5/12=4.54 mol
Moles H=
Moles O=

Then, divide all these moles each by the lowest in the table above. That will give you the empirical formula, example
where the mole mass is 220
Moles C= 3.2
Moles H= 6.4
Moles O= 19
divide by lowest, 3.2
Moles C= 1
Moles H= 2
Moles O= 6
CH2O6 empirical formula, emperical molmass is 12+2+6*16= 110 Divide this into the given mol mass (220/110=2), so multiply the atom ratios by this: mol formula C2H4O12

So finish the problem, if you get stuck, repost


how do u get the empirical molmass ?? nowher in the sample ugave s thre a 12 2 a 6 and why multiply by 16??


The empirial mass is the sum of the atoms atomic mass in the empirical formula

CH2O6 C is 12, H is 1, but there are two of them, and there are 6 O or 6*16. Sum is the empirical mass.

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