What are two observations made when a metal reacts with an acid?

When a metal reacts with an acid, one of the key observations is the production of bubbles, indicating the release of hydrogen gas as a byproduct of the reaction. This effervescence is a clear, visual sign of the chemical change occurring. Additionally, the metal will typically start to dissolve, effectively "disappearing" as it reacts with the acid to form a salt and hydrogen gas.

This combination of bubbling and the disappearing metal is a classic indication of a metal-acid reaction; it directly correlates to the formation of new substances. In contrast, other observations like color change, heat emission, or the formation of a solid (precipitate) may occur in different contexts or reactions but are not universally applicable to all metal-acid reactions. Thus, the observation of bubbles and the disappearance of the metal effectively capture the essence of the reaction taking place.