In the carbonate test, what observation indicates a positive result?

In the carbonate test, what observation indicates a positive result?

• A. The limewater turns milky/cloudy due to CO2.
• B. The limewater turns blue.
• C. The solution remains clear.
• D. The gas evolves is hydrogen.

Answer: (A)

When carbonate ions are tested, they react with acid to release carbon dioxide. A positive result is shown by the limewater turning milky or cloudy. This happens because the CO2 dissolves in the limewater (Ca(OH)2) and reacts to form calcium carbonate, which is insoluble and appears as a cloudy suspension: CO2 + Ca(OH)2 → CaCO3 + H2O. The milky appearance is the clear sign that CO2 is being produced and absorbed by the limewater. Other observations, like limewater turning blue, the solution staying clear, or hydrogen gas evolving, do not indicate a carbonate reaction.

When carbonate ions are tested, they react with acid to release carbon dioxide. A positive result is shown by the limewater turning milky or cloudy. This happens because the CO2 dissolves in the limewater (Ca(OH)2) and reacts to form calcium carbonate, which is insoluble and appears as a cloudy suspension: CO2 + Ca(OH)2 → CaCO3 + H2O. The milky appearance is the clear sign that CO2 is being produced and absorbed by the limewater. Other observations, like limewater turning blue, the solution staying clear, or hydrogen gas evolving, do not indicate a carbonate reaction.