When calcium carbonate reacts with hydrochloric acid, what is the observable effect?

When calcium carbonate reacts with hydrochloric acid, the observable effect is fizzing, which indicates the production of gas—specifically carbon dioxide. The reaction can be represented by the following chemical equation:

[ \text{CaCO}_3 (s) + 2 \text{HCl} (aq) \rightarrow \text{CaCl}_2 (aq) + \text{H}_2\text{O} (l) + \text{CO}_2 (g) \uparrow ]

In this reaction, calcium carbonate (a solid) reacts with hydrochloric acid to form calcium chloride (a soluble salt), water, and carbon dioxide gas. The fizzing occurs as the carbon dioxide gas escapes from the mixture, which can be observed as bubbles. This gas release is a clear indication of a chemical reaction taking place.

Other options have different processes or outcomes. For instance, changing color may happen in certain reactions, but it does not occur in this particular reaction between calcium carbonate and hydrochloric acid. Solidification is not applicable in this case as the reaction results in soluble products rather than the formation of a solid. While calcium carbonate does dissolve in dilute hydrochloric acid, the primary observable feature during the reaction is indeed the