Problem: Ibuprofen has the following mass percent composition. What is the empirical formula of ibuprofen?C: 75.69%H: 8.80%O: 15.51%

We’re being asked to determine the empirical formula of ibuprofen, a compound composed of C, H, and O given the mass percent of C, H, and O. This means we need to do the following steps:

Step 1: Calculate the mass and moles of C, H, and O in the compound.

Step 2: Determine the lowest whole number ratio of C, H, and O to get the empirical formula.

Step 1: The compound is composed of C, H, O we’re given the mass percent of C (75.69% C), H (8.80% H) and O (15.51 % O). 

Recall that mass percent is given by:

$\boxed{\mathbf{M}\mathbf{a}\mathbf{s}\mathbf{s}\mathbf{ }\mathbf{\%}\mathbf{ }\mathbf{=}\mathbf{ }\frac{\mathbf{m}\mathbf{a}\mathbf{s}\mathbf{s}\mathbf{ }\mathbf{o}\mathbf{f}\mathbf{ }\mathbf{e}\mathbf{l}\mathbf{e}\mathbf{m}\mathbf{e}\mathbf{n}\mathbf{t}}{\mathbf{t}\mathbf{o}\mathbf{t}\mathbf{a}\mathbf{l}\mathbf{ }\mathbf{m}\mathbf{a}\mathbf{s}\mathbf{s}\mathbf{ }\mathbf{o}\mathbf{f}\mathbf{ }\mathbf{c}\mathbf{o}\mathbf{m}\mathbf{p}\mathbf{o}\mathbf{u}\mathbf{n}\mathbf{d}}\mathbf{\times }\mathbf{100}\mathbf{\%}}$

Assuming we have 100 g of the compound, this means we have 75.69 g C, 8.80 g H, and 15.51 g O.