Which metal will react most readily with hydrochloric acid to release hydrogen gas?

Which metal will react most readily with hydrochloric acid to release hydrogen gas?

• A. Aluminum
• B. Copper
• C. Silver
• D. Gold

Answer: (A)

Metals that are more reactive than hydrogen will push hydrogen out of acids, producing hydrogen gas. Aluminum fits this, so it readily reacts with hydrochloric acid. The reaction can be written as 2 Al + 6 HCl → 2 AlCl3 + 3 H2, showing both the formation of aluminum chloride in solution and the release of H2 gas. The oxide layer on aluminum is quickly dissolved in the acidic environment, allowing the metal to keep reacting. The other metals listed are less reactive than hydrogen, so they don’t drive the reduction of H+ to H2 with hydrochloric acid under ordinary conditions. Copper, silver, and gold will remain largely unreactive with HCl in this context, so no hydrogen gas is produced.

Metals that are more reactive than hydrogen will push hydrogen out of acids, producing hydrogen gas. Aluminum fits this, so it readily reacts with hydrochloric acid. The reaction can be written as 2 Al + 6 HCl → 2 AlCl3 + 3 H2, showing both the formation of aluminum chloride in solution and the release of H2 gas. The oxide layer on aluminum is quickly dissolved in the acidic environment, allowing the metal to keep reacting.

The other metals listed are less reactive than hydrogen, so they don’t drive the reduction of H+ to H2 with hydrochloric acid under ordinary conditions. Copper, silver, and gold will remain largely unreactive with HCl in this context, so no hydrogen gas is produced.