Question

Butyric acid contains only C,H,O. A 4.24mg sample of butyric acid is completely burnt. It gives 8.45mg of CO2 and 3.46mg of H2O. What is the mass percentage of each element in butyric acid? The molecular mass of butyric acid was determined by experiment to be 88 a.m.u. What is the molecular formula?

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Answer 1

In CO2 the no of C atom is 1.
it means 44 mg of CO2 = 12 mg C
and 8.45 mg = 12 X 8.45 / 44
=2.30mg
% of C = 2.30 X 100 / 4.24
= 54.3 %
Similarly in H2O = 2H
in 3.46mg of H2O H = 2 X 3.46 /18
= 0.384mg
% of H = 0.348 x100 / 4.24 =9 %
% of O = 100 - 63.3
= 36.7%
By calculation we get the simple whole no ratio = 2:4:1
so empirical formula is C2H4O
and the value of n= 88 /44 =2
so molecular formula = c4 H8 O2