How can you test for carbonate ions in a sample?

How can you test for carbonate ions in a sample?

• A. Add dilute acid; CO2 produced; limewater turns cloudy if CO2 present.
• B. Add base and observe color change.
• C. Add oxidizing agent and heat.
• D. Pass CO2 gas through limewater.

Answer: (A)

Testing for carbonate ions relies on their reaction with acids to release carbon dioxide, which limewater can detect. When you add a dilute acid to a solution containing carbonate ions, the carbonate reacts to form carbon dioxide, water, and a salt. The fizzing you see comes from the CO2 gas being produced. That CO2 then reacts with limewater (calcium hydroxide) to form calcium carbonate, which is insoluble and makes the limewater turn cloudy. This visible milky change gives a clear yes-or-no indication that carbonate ions were present. If carbonate ions aren’t in the sample, no CO2 is produced, so the limewater stays clear. Other options don’t provide this direct link: adding a base won’t give a distinctive signal for carbonate ions, an oxidizing agent with heat doesn’t specifically reveal carbonates, and passing CO2 gas through limewater tests for CO2 in a gas sample rather than carbonate ions in a liquid.

Testing for carbonate ions relies on their reaction with acids to release carbon dioxide, which limewater can detect. When you add a dilute acid to a solution containing carbonate ions, the carbonate reacts to form carbon dioxide, water, and a salt. The fizzing you see comes from the CO2 gas being produced. That CO2 then reacts with limewater (calcium hydroxide) to form calcium carbonate, which is insoluble and makes the limewater turn cloudy. This visible milky change gives a clear yes-or-no indication that carbonate ions were present.

If carbonate ions aren’t in the sample, no CO2 is produced, so the limewater stays clear. Other options don’t provide this direct link: adding a base won’t give a distinctive signal for carbonate ions, an oxidizing agent with heat doesn’t specifically reveal carbonates, and passing CO2 gas through limewater tests for CO2 in a gas sample rather than carbonate ions in a liquid.