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Question
Tue June 12, 2012 By:

# Adipic acid is used in the commercial manufacture of Nylon. The composition of the acid is 49.3% C, 6.9% H, and 43.8% O by mass. The molecular weight is 146 amu. What is the molecular formula for Adipic Acid?

Tue June 12, 2012

The composition of adipic acid given is:

C = 49.3%

H = 6.9%

O = 43.8%

Let's assume that we have 100 grams of adipic acid. So, the mass of C, H and O in 100g of adipic acid are:

C = 49.3 g

H = 6.9 g

O = 43.8 g

Now we will find the no. of moles of each:

Number of moles = weight of the element/atomic mass

C = 49.3/12.01 = 4.10 moles

H = 6.9/1.01 = 6.9 moles

O = 43.8/16.0 = 2.73 moles

Now the mole ratios of the following are:

C = 4.10/2.73 = 1.50

H = 6.9/2.73 = 2.52

O = 2.73/2.73 = 1.0

Reduce the fraction to whole numbers by dividing them by 2;

C = 3, H = 5, O = 2

Hence, the empirical formula is C3H3O2

The empirical formula weight = 12.01 X 3 + 1.01 X 5 + 16.0 X 2 = 73.08 g

Molecular weight = (empirical formula weight) X n

So, n = 146/73.08 = 2 (approx)

So, the molecular formula is: (C3H5O2)2 or C6H10O4
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