metal +acid

Hydrochloric acid is the aqueous solution of hydrogen chloride gas. No matter how concentrated is hydrochloric acid, the HCl molecules would ionized in water to give H+(aq) and Cl-(aq) ions. Therefore, lead or more reactive metals would react with H+(aq) in the concentrated hydrochloric acid to give hydrogen gas.

For example, zinc would react with concentrated hydrochloric acid to give hydrogen gas. The equation is:
Zn(s) + HCl(aq) → ZnCl2(aq) + H2(g)
or: Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g)
=