Question

The molecular mass of an organic compound is 90 and its %age composition is C- 26.6%; O=71.1%



and H=2.2%. Determine the molecular formula of the compound.

Answer 1

  Assume that you have 100 g of acid. Based on the percentages given above, it would contain 26.7 g of C, 2.2 g of H, and 71.1 g of O. Convert these masses to moles. 

moles C = 26.7 / 12.0 = 2.22 
moles H = 2.2 / 1.0 = 2.2 
moles O = 71.1 / 16.0 = 4.44 

Dividing by the smallest (2.2) we find that the mole ratio of C:H:O = 1:1:2, so the empirical formula is CHO2. 

The formula weight of CH2O = 12.0 + 1.0 + 2(16.0) = 45.0. Since the molecular weight is 90, then there are 2 CH2O units (45 each) in the moleculke. The molecular formula is 2 x CHO2 = C2H2O4.

Answer 2

Answer:C2H2O4

Explanation:

Let the molar mass of compound is 100 g

Number of moles of C in compound = 26.6/12 = 2.216

Number of moles of O in Compound = 71.1/16 = 4.44

Number of moles of H in compound = 2.2/1 = 2.2

Simple whole number ratio of mole of C, O and H is 1 : 2 :1

Empirical Formula = CHO2

​Empirical formula mass = 12 g + 1 g + 32 g = 45 g

Molecular mass of the compound is 90 g

Molecular formula = (empirical formula)n

n = Molar mass/empirical formula mass

n = 90 /45 = 2

So the molecular formula would be (CHO2)2 = C2H2O4

Hope this helps!!