Question

In a laboratory, Selima added five drops of hydrochloric acid to a container with sodium bicarbonate. Which observation helps her determine whether a chemical change has taken place?

a) Bubbles and fizzing occur.
b) The mixture changes color.
c) The temperature decreases.
d) The mixture becomes denser.

Answer 1

Bubbles and fizzing occurring when hydrochloric acid is added to sodium bicarbonate is a key indicator of a chemical change, as it signifies the release of carbon dioxide gas from the reaction between an acid and a bicarbonate.

Step-by-step explanation:

When Selima added hydrochloric acid to sodium bicarbonate, the observation that would help her determine whether a chemical change has taken place is a) Bubbles and fizzing occur. This is a classic reaction between an acid and a bicarbonate, where the release of carbon dioxide gas produces the fizzing and bubbling effect, indicating a chemical change. Other observations that might indicate a chemical reaction include temperature changes, light emission, and unexpected color changes. However, in this particular scenario of mixing hydrochloric acid with sodium bicarbonate, the formation of a gas as evidenced by bubbling is the primary indicator of a chemical change.