Adding acid produces a gas that turns limewater milky. Which ion is present?

Adding acid produces a gas that turns limewater milky. Which ion is present?

• A. Carbonate (CO3 2-)
• B. Sulfite (SO3 2-)
• C. Nitrate (NO3-)
• D. Chloride (Cl-)

Answer: (A)

Gas produced when an acid reacts with a carbonate is carbon dioxide. The CO2 turns limewater cloudy because it reacts with calcium hydroxide to form calcium carbonate, a white insoluble solid. So seeing a gas that makes limewater milky indicates carbonate ions are present: CO3^2−. If the ion were sulfite, acid would release sulfur dioxide, not CO2, and wouldn’t produce the characteristic milky limewater. Nitrate and chloride ions don’t release a gas on acidification in this test, so they wouldn’t cause the limewater to turn cloudy.

Gas produced when an acid reacts with a carbonate is carbon dioxide. The CO2 turns limewater cloudy because it reacts with calcium hydroxide to form calcium carbonate, a white insoluble solid. So seeing a gas that makes limewater milky indicates carbonate ions are present: CO3^2−.

If the ion were sulfite, acid would release sulfur dioxide, not CO2, and wouldn’t produce the characteristic milky limewater. Nitrate and chloride ions don’t release a gas on acidification in this test, so they wouldn’t cause the limewater to turn cloudy.