1. Assume a 100g Sample

* This makes the percentages directly into grams:

* 39.81 g Cu

* 20.06 g S

* (100 - 39.81 - 20.06) = 40.13 g O

2. Convert Grams to Moles

* Divide each element's mass by its molar mass:

* Cu: 39.81 g / 63.55 g/mol = 0.627 mol

* S: 20.06 g / 32.06 g/mol = 0.626 mol

* O: 40.13 g / 16.00 g/mol = 2.51 mol

3. Find the Simplest Mole Ratio

* Divide each mole value by the smallest mole value (0.626 mol):

* Cu: 0.627 mol / 0.626 mol ≈ 1

* S: 0.626 mol / 0.626 mol ≈ 1

* O: 2.51 mol / 0.626 mol ≈ 4

4. Empirical Formula

* The empirical formula represents the simplest whole-number ratio of atoms in the compound. Therefore, the empirical formula is CuSO₄.

Can this be the molecular formula?

* It's possible that the empirical formula is also the molecular formula. However, we need more information to confirm this. To determine the molecular formula, we would need the molar mass of the compound.

Here's why:

* The empirical formula only tells us the simplest ratio of atoms.

* The molecular formula represents the actual number of atoms in a molecule.

Example:

* If the molar mass of the compound is 159.61 g/mol, then the molecular formula is the same as the empirical formula (CuSO₄) because the molar mass of CuSO₄ is 159.61 g/mol.

* However, if the molar mass of the compound is 319.22 g/mol, then the molecular formula would be Cu₂S₂O₈ (twice the empirical formula).