Final answer:
Zinc metal reacts with concentrated hydrochloric acid in a single displacement reaction to form zinc chloride and release hydrogen gas as bubbles.
Step-by-step explanation:
When a small piece of zinc metal is dropped into a solution of concentrated hydrochloric acid, a chemical reaction occurs. This reaction is a single displacement reaction where zinc replaces hydrogen in hydrochloric acid forming zinc chloride and hydrogen gas. The bubbles of gas you observe are due to the evolution of hydrogen gas, which is a common observable indication of this reaction taking place.
To describe the reaction step-by-step: First, the zinc metal reacts with the hydrochloric acid. Zinc is more reactive than hydrogen and displaces it from hydrochloric acid. As a result, zinc chloride, a soluble salt, is formed, and hydrogen gas is released as bubbles.
The chemical equation representing this reaction is: Zn(s) + 2HCl(aq) -> ZnCl2(aq) + H2(g)