Question

question 8 12.5 pts why is an acid - base indicator used in the experiment? it provides evidence that the sodium bicarbonate has finished decomposing. it provides evidence that carbon dioxide and water is produced. it provides evidence that protonated water is being produced. it provides evidence that sodium oxide is produced.

Explanation:

To determine the answer, we analyze the role of an acid - base indicator. An acid - base indicator shows changes (like color change) based on the presence of $H^+$ (protonated species) or $OH^-$ ions. When a reaction involves protonation/deprotonation of water (e.g., in reactions where water acts as a base or acid), the indicator can detect the change in protonated water concentration.

• Option 1: Acid - base indicators don't directly show if sodium bicarbonate has finished decomposing. Decomposition of $NaHCO_3$ is a thermal decomposition (e.g., $2NaHCO_3\xrightarrow{\Delta}Na_2CO_3 + CO_2 + H_2O$), and an acid - base indicator isn't used to detect the completion of this decomposition in the typical sense.
• Option 2: Detecting $CO_2$ and $H_2O$ production from $NaHCO_3$ decomposition is not the role of an acid - base indicator. $CO_2$ is a gas and $H_2O$ is a liquid, and acid - base indicators respond to $H^+$ or $OH^-$ concentration, not directly to the presence of these substances.
• Option 3: In reactions where water is protonated (e.g., in acid - base reactions where water acts as a base and accepts a proton to form $H_3O^+$), the acid - base indicator can show the change in the concentration of protonated water (hydronium ions) by changing color. This is the correct role of an acid - base indicator.
• Option 4: Sodium oxide production is not related to the function of an acid - base indicator. Acid - base indicators deal with $H^+$ and $OH^-$ ions, not the formation of metal oxides.

Answer:

The correct option is the one stating "It provides evidence that protonated water is being produced." (The option with the text "It provides evidence that protonated water is being produced.")