We’re being asked to **determine the empirical formula** of an unknown compound given the **mass percent of C, H, and O**.

Recall that the ** empirical formula** is the simplest whole-number ratio formula of a compound.

**Step 1:** Recall that ** mass percent** is given by:

$\overline{){\mathbf{\%}}{\mathbf{}}{\mathbf{mass}}{\mathbf{=}}\frac{\mathbf{mass}\mathbf{}\mathbf{of}\mathbf{}\mathbf{X}}{\mathbf{total}\mathbf{}\mathbf{mass}}{\mathbf{\times}}{\mathbf{100}}}$

The problem states that the compound is **74.97% C, 8.39 % H,** and **16.64% O**. Assuming we have **100 g** of the compound, this means we have **74.97 g C, 8.39 H,** and **16.64 g O**.

Now, we need to get the moles of each element in the compound.

The atomic masses are **12.01 g/mol C, 1.01 g/mol H,** and **16.00 g/mol O**.

An unknown compound was determined to be 74.97% carbon, 8.39% hydrogen, and 16.64% oxygen. Calculate the empirical formula.