How to test carbon dioxide?

The primary method to test for the presence of carbon dioxide involves using limewater.

Testing for Carbon Dioxide with Limewater

Limewater, a solution of calcium hydroxide, provides a simple and effective way to detect carbon dioxide. The key observation is a color change in the limewater when carbon dioxide is introduced.

Here's how the test works:

1. Prepare Limewater: Ensure you have a clear solution of limewater.
2. Introduce the Gas: Bubble the gas you suspect contains carbon dioxide through the limewater. This can be done using a delivery tube.
3. Observe the Change: Watch carefully for any changes in the appearance of the limewater.

Expected Result

• Positive Result: If carbon dioxide is present, the limewater will turn milky or cloudy white. This cloudiness is due to the formation of insoluble calcium carbonate.

• Negative Result: If the limewater remains clear, carbon dioxide is likely absent.

Chemical Reaction

The reaction that occurs is as follows:

Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)

Calcium hydroxide (limewater) + Carbon dioxide → Calcium carbonate (milky precipitate) + Water

Summary Table

Test	Reagent	Observation	Conclusion
Carbon Dioxide	Limewater	Limewater turns milky/cloudy	Carbon dioxide is present
		Limewater remains clear	Carbon dioxide is likely absent