Here's how to calculate the formula mass:
* Nitrogen (N): 2 atoms * 14.01 g/mol = 28.02 g/mol
* Hydrogen (H): 8 atoms * 1.01 g/mol = 8.08 g/mol
* Sulfur (S): 1 atom * 32.07 g/mol = 32.07 g/mol
* Oxygen (O): 4 atoms * 16.00 g/mol = 64.00 g/mol
Total Formula Mass: 28.02 + 8.08 + 32.07 + 64.00 = 132.17 g/mol
Therefore, the formula mass of ammonium sulfate ((NH₄)₂SO₄) is 132.17 g/mol.