Demonstration through experiment of breathing out air into limewater that carbon dioxide is exhaled during respiration

 

Abstract:

This experiment demonstrates the presence of carbon dioxide exhaled during respiration by bubbling exhaled air into limewater, resulting in the formation of a precipitate of calcium carbonate.

Introduction:

Respiration is the process through which organisms release energy from food molecules. During respiration, carbon dioxide is produced as a waste product. This experiment aims to demonstrate the presence of carbon dioxide in exhaled air by bubbling it into limewater, a solution of calcium hydroxide. When carbon dioxide reacts with limewater, it forms calcium carbonate, which is insoluble and appears as a white precipitate.

Materials:

• Limewater (calcium hydroxide solution)
• Straw or glass tubing
• Funnel
• Test tube
• Breath collection bag

Procedure:

1. Prepare a solution of limewater by dissolving calcium hydroxide in water.
2. Collect exhaled air into a breath collection bag by exhaling into it.
3. Insert one end of a straw or glass tubing into the breath collection bag and the other end into a funnel attached to a test tube containing limewater.
4. Bubble the exhaled air through the limewater for a few minutes.
5. Observe any changes in the limewater.

Observations:

Initially, the limewater is clear. As exhaled air containing carbon dioxide is bubbled through the limewater, it turns milky due to the formation of calcium carbonate precipitate.

Calculation:

No specific calculations are required for this experiment.

Precautions:

• Handle limewater with care as it is a corrosive substance.
• Avoid inhaling directly from the limewater to prevent exposure to harmful gases.
• Ensure the test tube is securely attached to the funnel to prevent spills.

Results:

Experiment Trial	Observations
1	Limewater turned milky after bubbling exhaled air
2	Similar observation as trial 1

Short Questions and Answers

1. What is the purpose of the experiment?

   The purpose is to demonstrate the presence of carbon dioxide exhaled during respiration.

2. What is limewater?

   Limewater is a solution of calcium hydroxide in water.

3. What happens when carbon dioxide is bubbled through limewater?

   It forms a white precipitate of calcium carbonate.

4. How is exhaled air collected?

   Exhaled air is collected into a breath collection bag by exhaling into it.

5. What material is used to bubble exhaled air into limewater?

   A straw or glass tubing is used.

6. Why is limewater initially clear?

   Limewater is initially clear because it does not contain any precipitate.

7. What is the chemical formula of limewater?

   The chemical formula is Ca(OH)₂.

8. What safety precaution should be taken while handling limewater?

   Limewater should be handled with care as it is a corrosive substance.

9. Why is a funnel attached to the test tube?

   A funnel is attached to facilitate the bubbling of exhaled air into the limewater and to prevent spills.

10. What is the appearance of the precipitate formed?

    The precipitate appears as a white, milky substance.

11. How can the presence of carbon dioxide be confirmed?

    The presence of carbon dioxide can be confirmed by observing the formation of the white precipitate in the limewater.

12. What is the role of calcium hydroxide in the experiment?

    Calcium hydroxide reacts with carbon dioxide to form calcium carbonate.

13. What change is observed in the limewater after bubbling exhaled air?

    The limewater turns milky.

14. What is the chemical name of the precipitate formed?

    The precipitate formed is calcium carbonate.

15. Why should one avoid inhaling directly from the limewater?

    To prevent exposure to harmful gases that may be present in the limewater.

16. How is the test tube secured during the experiment?

    The test tube is securely attached to the funnel.

17. What is the consistency of the precipitate formed?

    The precipitate is insoluble in water and appears as a solid.

18. What should be done if limewater spills?

    Limewater spills should be cleaned immediately with water.

19. What is the purpose of recording observations?

    Recording observations helps in documenting the results of the experiment.

20. What is the significance of this experiment?

    This experiment demonstrates a biological process (respiration) and its chemical outcome (formation of calcium carbonate), illustrating the interconnectedness of biology and chemistry.

Multiple Choice Questions

1. What is the purpose of bubbling exhaled air into limewater in this experiment?
   A. To produce oxygen
   B. To demonstrate the presence of carbon dioxide
   C. To measure the rate of respiration
   D. To increase the pH of limewater
   Answer: B. To demonstrate the presence of carbon dioxide
2. Which substance is bubbled into limewater during the experiment?
   A. Nitrogen
   B. Oxygen
   C. Carbon dioxide
   D. Hydrogen
   Answer: C. Carbon dioxide
3. What change is observed in the limewater after bubbling exhaled air?
   A. It turns green
   B. It remains clear
   C. It turns milky
   D. It becomes yellow
   Answer: C. It turns milky
4. What is the chemical formula of the precipitate formed in the limewater?
   A. CaCO₂
   B. Ca(OH)₂
   C. CO₂
   D. CaCO₃
   Answer: D. CaCO₃
5. What precaution should be taken while handling limewater?
   A. Wear gloves
   B. Avoid contact with skin
   C. Dispose of it in the sink
   D. Heat it to a high temperature
   Answer: B. Avoid contact with skin