What is the percentage by mass of oxygen in Al2(SO4)3. 2H2O? [Al = 27, S = 32, H = 1, O = 16]

To calculate the percentage by mass of oxygen in Al2(SO4)3.2H2O, we need to find the total mass of the compound and the mass of oxygen in the compound. First, let's calculate the total mass of the compound: 2 atoms of Al x 27 g/mol = 54 g/mol 3 atoms of S x 32 g/mol = 96 g/mol 14 atoms of O x 16 g/mol = 224 g/mol 4 atoms of H x 1 g/mol = 4 g/mol Total mass = 54 + 96 + 224 + 4 = 378 g/mol Next, let's calculate the mass of oxygen in the compound: 14 atoms of O x 16 g/mol = 224 g/mol Now we can calculate the percentage by mass of oxygen in the compound: (Mass of oxygen / Total mass) x 100% = (224 g/mol / 378 g/mol) x 100% = 59.25% Therefore, the answer is 59.25%.