Which metal will release H2 gas when it reacts with hydrochloric acid?

Which metal will release H2 gas when it reacts with hydrochloric acid?

• A. Au
• B. Zn
• C. Hg
• D. Ag

Answer: (B)

Metals that are more reactive than hydrogen will push hydrogen out of acids, producing hydrogen gas. In hydrochloric acid, zinc can donate electrons to reduce H+ to H2, so it undergoes oxidation to Zn2+ while the hydrogen gas is released. The overall reaction is Zn + 2HCl → ZnCl2 + H2. Gold and silver are much less reactive than hydrogen, so they don’t displace hydrogen from HCl and no H2 is produced under normal conditions. Mercury doesn’t react with dilute hydrochloric acid to liberate hydrogen gas either, though it can react with stronger oxidizing acids. So zinc is the metal that releases hydrogen gas with hydrochloric acid.

Metals that are more reactive than hydrogen will push hydrogen out of acids, producing hydrogen gas. In hydrochloric acid, zinc can donate electrons to reduce H+ to H2, so it undergoes oxidation to Zn2+ while the hydrogen gas is released. The overall reaction is Zn + 2HCl → ZnCl2 + H2.

Gold and silver are much less reactive than hydrogen, so they don’t displace hydrogen from HCl and no H2 is produced under normal conditions. Mercury doesn’t react with dilute hydrochloric acid to liberate hydrogen gas either, though it can react with stronger oxidizing acids. So zinc is the metal that releases hydrogen gas with hydrochloric acid.