In a science demonstration, a teacher mixed zinc (Zn) with hydrogen chloride (HCl) in a flask and quickly attached a balloon over the mouth of the flask. Bubbles formed in the solution and the balloon inflated.

Question

What most likely occurred during this demonstration?

The Zn and HCl both retained their identity.
Either Zn or HCl, but not both, retained its identity.
Evaporation of one of the substances occurred.
One or more new substances formed.

Answer 1

In this demonstration, when zinc (Zn) is mixed with hydrogen chloride (HCl), a chemical reaction occurs. Zinc reacts with hydrochloric acid to produce zinc chloride (ZnCl2) and hydrogen gas (H2). The formation of bubbles in the solution indicates that a gas is being released, which is the hydrogen gas produced in the reaction. As the gas is produced, it inflates the balloon attached to the flask.

Since a new gas (hydrogen) is generated from the reaction between zinc and hydrochloric acid, this indicates that one or more new substances formed during the demonstration. Therefore, the correct conclusion is:

One or more new substances formed.