chemical analysis of an organic compound found the following composition: 40.0% c, 53.5% o, and 6.7% h. if the molar mass is 180.2 g/mol, how many empirical formula units are there in the molecular formula?



Answer :

Empirical formula units is 2 and the molecular formula is CxHyOz.

Molar mass-The molar mass of a chemical compound is determined by dividing its mass by the quantity of that compound, expressed as the number of moles in the sample, measured in moles. The molar mass of a substance is a bulk attribute rather than a molecular one.Calculate the molar mass of a substance by adding the molar masses of its constituent atoms.

There are 40.0 in 100 g of the unknown.

40.0⋅g/12.011⋅g⋅mol−1C

6.7⋅g/1.00794⋅g⋅mol−1 H and

53.5⋅g/16.00gmol−1  

We divide by to get C : H : O.

=3.33:6.65:3.34

. We get an empirical formula of C H 2 O by dividing each elemental ratio by the LOWEST number, which is close enough to WHOLE numbers.

Now the molecular formula is always a multiple of the empirical formula; i.e.

(EF)n=MF.

So 60.0⋅g.mol−1=n×(12.011+2×1.00794+16.00)g⋅mol−1.

Clearly n=2, and the molecular formula is×(CH2O) =CxHyOz.

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