Ibuprofen, an aspirin substitute, has a mass percent composition of 75.69% C, 8.80% H, and 15.51% O. Calculate its empirical formula.

C₁₃H₁₈O₂

Explanation:

Empirical formula is the simplest ratio in moles of the elements presents in the compound. Assuming a basis of 100g, we need to convert the mass of each element to moles and, find the ratio of each of these:

Moles C:

75.69g * (1mol / 12.01g) = 6.3 moles of C

Moles H:

8.80g * (1mol / 1.01g) = 8.7 moles of H

Moles O:

15.51g * (1mol / 16g) = 0.97 moles of O

The ratio dividing in the moles of O -Because is the element with the lower amount of moles-:

C = 6.3mol / 0.97mol = 6.5

H = 8.7mol / 0.97mol = 9

O = 0.97mol / 0.97mol = 1

As the ratio must be in whole-numbers, multiplying in 2:

C = 13;

H = 18

O = 2

And empirical formula is:

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