vitamin C (absorbic acid) contains 40.92% C, 4.58%H , and 54.50 O ?? what is the empirical formula for vitamin C

Question

 vitamin C (absorbic acid) contains 40.92% C, 4.58%H , and 54.50 O ?? what is the empirical formula for vitamin C

Answer 1

When given % composition, and asked for the empirical formula, it is easiest to just assume 100 g of material. Thus,

Mass C = 40.92 g.  Moles C = 40.92 g x 1 mole/12 g = 3.41 moles C

Mass H = 4.58 g.  Moles H = 4.58 g x 1 mole/1.0 g = 4.58 moles H

Mass O = 54.50 g.  Moles O = 54.50 g x 1 mole/16 g = 3.41 moles O

Next, we want to get the moles into whole numbers, so we begin by dividing all by the smallest, i.e. divide all by 3.41.

Moles C = 3.41/3.41 = 1

Moles H = 4.58/3.41 = 1.34

Moles O = 3.41/3.41 = 1

Now, in order to get 1.34 to be a whole number we multiply it (and all others) by 3

Moles C = 1x3 = 3

Moles H = 1.34x3 = 4

Moles O = 1x3 = 3

Empirical Formula = C₃H₄O₃