Identification of Carbon Dioxide in Exhaled Air

 Gaseous Exchange and Respiration

During respiration, living cells oxidize food substance to produce carbon dioxide. Carbon dioxide is a waste product and must be removed from the body. The blood carries carbon dioxide to the lungs where is it released in exhalation.

Learning Objectives

To identify the presence of carbon dioxide in exhaled air.

Materials

Clear plastic container, plastic straw, lime water*.

Activity Procedure

1.           Put approximately 10 mL of lime water into a clear container.

2.           Blow exhaled air through the straw and into the limewater until a change is observed.

Results and Conclusion

The addition of carbon dioxide turns limewater milky (white). This shows that carbon dioxide is present in exhaled air.

Figure 6.9: Identifying the by product CO2 in respiration

Clean Up Procedure

1.           Unused lime water should be stored in an airtight labeled bottle for future use.

2.           Used lime water contains suspended solids and should be disposed out-side, not down the drain.

Notes

Lime water reacts with carbon dioxide to form white calcium carbonate precipitate.

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