Investigating the Differences Between Inspired and Expired Air

A simple experiment using limewater can be carried out to compare the levels of carbon dioxide in inhaled (inspired) and exhaled (expired) air.

Apparatus Setup:

• Two boiling tubes are used: Boiling Tube A and Boiling Tube B.
• Both tubes contain limewater (a solution of calcium hydroxide).
• A mouthpiece and tubing allow the subject to breathe in through one tube and breathe out through the other.

Procedure:

1. When inhaling, air is drawn through Boiling Tube A.
2. When exhaling, air is blown into Boiling Tube B.
3. Limewater is naturally clear but turns cloudy or milky when carbon dioxide is present (due to the formation of calcium carbonate).

Observation and Conclusion:

• Boiling Tube A (inhaled air): The limewater remains clear because there is little carbon dioxide in the air we breathe in.
• Boiling Tube B (exhaled air): The limewater turns cloudy, indicating a higher concentration of carbon dioxide in exhaled air.

Conclusion:

This experiment demonstrates that exhaled air contains more carbon dioxide than inhaled air, as a result of respiration in body cells.