Consider the following reaction: 4Al(s) + 3O2(g) → 2Al2O3(s) It takes 15.7 L of pure oxygen gas at STP to react completely with a certain sample of aluminum. What mass of aluminum reacted?

Answer 1

At STP, 1 mole occupies 22.4 L; use this to find moles of O₂ and then do normal stoichiometry:

(15.7 L) * (1 mol gas / 22.4 L) * (4 mol Al / 3 mol O₂) * (26.98g Al / 1 mol Al) = 25.2g Al.