Determine the molecular formula of a compound if it is composed of 40.92% carbon, 4.58% hydrogen, and 54.50% oxygen. The molar mass is 176.12 g/mol. A) C3H8O3.
B) CH2O.
C) C2H3O2.
D) C3H4O3.

No correct answer listed. See explanation for defense.

Explanation:

Given

C: 40.92% => 40.92g/100wt => (40.92/12)moles C = 3.41 moles O

H:   4.58% =>   4.58g/100wt =>      (4.58/1)moles H = 4.58 moles H

O: 54.50% => 54.5g/100wt =>     (54.5/16)moles O = 3.41 moles O

Empirical ratio => C : H: O => (3.41/3.41) : (4.58/3.41) : (3.41/3.41) => 1 : 1.34 : 1

=> C : H : O => 3(1 : 1.34 : 1) => 3 : 4 : 3 => Empirical Formula C₃H₄O₃

Molecular Weight = Empirical Formula Wt x N

         176.12          =           88  x  N

N = whole number multiple of empirical formula = 176.12/88 = 2

∴ Molecular Formula => (C₃H₄O₃)₂ => C₆H₈O₆

Note => Only ionic compounds (salts) have subscripts reduced to lowest whole number ratios. Molecular compounds as C₆H₈O₆ are not reduced to lowest whole number ratios. Therefore, there is no correct answer in the answer choice list for the 'Molecular Formula'. Doc :-)

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