The elemental mass percent composition of ibuprofen (a nonsteroidal anti-inflammatory drug [NSAID]) is 75.69% C, 8.80% H, and 15.51% O. Determine the empirical formula of ibuprofen.

C13H18O2

Explanation:

We can then divide these masses by the molar masses of the elements to determine the number of moles of each element present in the 100 - g sample:

mol C = 75.69 (g/C) / 12.01 (g/mol) = 6.302 mol C

mol H = 8.8g (g/H) / 1.008 (g/mol) = 8.7 mol H

mol O = 15.51 (g/O) / 16.00 (g/mol) = 0.969 mol O

The smallest mole quantity is then divided into itself and the others to give rise to a crude empirical formula:

6.302/0.969 = 6.5 C

8.7/0.969 = 9.0 H

0.969/0.969 = 1.0 O

so the crude empirical formula = C6.5H9O, Although this formula does contain the proper ratio, it does not contain only whole numbers. Because of this, we multiply each term by a common factor that will make all the numbers whole. In this case the only fractional subscript is 6.5 on carbon, so the lowest factor we can multiply to get 6.5 to a whole number is 2. The answer is C13H18O2

Answer: C7 H9 O

Explanation:

Lets assume that the total mass is 100 grams so that

the mass of each element = the percent given

Given that; C = 75.69g, H = 8.8g and O = 15.51g

Convert the mass of each element to moles using the molar mass

75.69g C * 1 mol C : 12g C = 6.3075 mol C

8.8g H * 1 mol H : 1.01g H = 8.8 mol H

15.51g O * 1 mol O : 16g O = 0.969375 mol O

Divide each mole value by the smallest number of moles calculated. Round to the nearest whole number.

6.3075 : 0.969375 mol C = 6.506 ≈ 7

8.8 : 0.969375 mol H = 9.0

0.969375 : 0.969375 mol O = 1

∴ The empirical formula for Ibuprofen is C7 H9 O (the numbers which are the mole ratio are in subscripts).