Investigate the differences in composition between inspired and expired air using limewater as a test for carbon dioxide
Investigate the differences in composition between inspired and expired air using limewater as a test for carbon dioxide
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To investigate the differences in composition between inspired (inhaled) and expired (exhaled) air, we can utilize limewater as a test for carbon dioxide. Here’s a detailed overview of the differences in air composition and the limewater test procedure.
Differences in Composition
Composition of Inspired vs. Expired Air
| Gas | Inspired Air | Expired Air | Reason for Difference |
|---|---|---|---|
| Oxygen (O₂) | 21% | 16% | Oxygen is absorbed by the blood during respiration. |
| Carbon Dioxide (CO₂) | 0.04% | 4% | CO₂ is produced by cellular respiration and diffuses into the lungs from the blood. |
| Water Vapour | Lower | Higher | Water evaporates from the moist lining of the alveoli into the expired air due to body temperature. |
| Nitrogen (N₂) | 78% | 78% | Nitrogen remains unchanged as it is not used by the body. |
The key differences are that expired air contains significantly more carbon dioxide and water vapor, and less oxygen compared to inspired air.
Limewater Test for Carbon Dioxide
Purpose
The limewater test is a simple and effective method to detect carbon dioxide in gases, such as expired air.
Chemical Reaction
When carbon dioxide is bubbled through limewater (a solution of calcium hydroxide), it reacts to form calcium carbonate, which precipitates out of solution, causing the limewater to turn milky:
Procedure
- Setup: Prepare two containers—one with clear limewater and another with plain water.
- Breathing Test:
- Exhale into the limewater using a straw or tube.
- Observe any changes in the limewater.
- Observation:
- If carbon dioxide is present, the limewater will turn cloudy or milky, indicating a positive result for CO₂.
- The water should remain clear if no CO₂ is present.
