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:

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

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**.

Ibuprofen has the following mass percent composition. What is the empirical formula of ibuprofen?

C: 75.69%

H: 8.80%

O: 15.51%

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