A 20 g mixture of Aluminum and Copper was treated with an excess of hydrochloric acid, releasing 6.72 L of hydrogen gas at STP. What is the mass fraction of Copper in the original mixture?
- 73%
- 27%
- 50%
- 36.5%
📝 Detailed explanation
Only Aluminum reacts: 2Al + 6HCl → 2AlCl₃ + 3H₂.n(H₂) = 6.72 / 22.4 = 0.3 mol.
n(Al) = 0.3 * (2 / 3) = 0.2 mol.
Mass Al = 0.2 * 27 = 5.4 g.
Mass Cu = 20 - 5.4 = 14.6 g.
Mass fraction Cu = 14.6 / 20 = 0.73 or 73%.