Answer: 509.8 g
Step-by-step explanation:
5 moles Al₂O₃
Al: 2 x 26.98 g = 53.96 g
O: 3 x 16.00 g = 48.00 g
Total grams = 101.96 g
1 mole of Al₂O₃ = 101.96 g
5 mol Al₂O₃ x (101.96 g Al₂O₃/1 mol Al₂O₃) = 509.8 g Al₂O₃
Note that moles of Al₂O₃ cancel and you are left with grams, which is what you want.