1. Convert grams to moles

* Copper (Cu): Divide the mass of copper by its molar mass (63.55 g/mol):

5.687 g Cu / 63.55 g/mol = 0.0895 mol Cu

* Oxygen (O): Divide the mass of oxygen by its molar mass (16.00 g/mol):

1.305 g O / 16.00 g/mol = 0.0816 mol O

2. Find the mole ratio

* Divide the number of moles of each element by the smallest number of moles:

* Cu: 0.0895 mol / 0.0816 mol = 1.095 ≈ 1.1

* O: 0.0816 mol / 0.0816 mol = 1

3. Simplify the ratio (if necessary)

* Since we have a ratio of approximately 1.1:1 for Cu:O, multiply both sides of the ratio by 10 to get whole numbers:

* Cu: 1.1 x 10 = 11

* O: 1 x 10 = 10

4. Write the empirical formula

* The empirical formula is Cu₁₁O₁₀.

Important Note: The empirical formula represents the simplest whole-number ratio of atoms in a compound. It's possible the actual molecular formula is a multiple of this empirical formula.