======Carbon Dioxide in Breath======


<WRAP right box>
**Materials: **{{$demo.materials_description}}\\
**Difficulty: **{{$demo.difficulty_description}}\\
**Safety: **{{$demo.safety_description}}\\
\\
**Categories:** {{$demo.categories}}
\\


**Alternative titles:** Comparing Carbon Dioxide in Inhaled and Exhaled Air
</WRAP>

====Summary====                   
{{$demo.summary}}



====Procedure====  
  -Set up two boiling tubes, each containing an equal amount of limewater.  
  -Insert a delivery tube into each boiling tube so the ends dip below the liquid surface.  
  -Connect both tubes to a T-piece mouthpiece so one tube is for inhaling and the other for exhaling.  
  -Check that all bungs are secure and the delivery tubes are at the same depth in the liquid.  
  -Breathe in gently through the apparatus, drawing air through one tube.  
  -Without removing the mouthpiece, breathe out through the other tube, bubbling air through the second liquid.  
  -Repeat inhaling and exhaling so that equal amounts of air pass through each liquid.  
  -Observe and record color or turbidity changes in the two tubes.



====Links==== 
Carbon dioxide content of inhaled and exhaled air - Caroline Osborne: 
{{youtube>1DWO-K75r_w?}}\\

To Investigate the Carbon Dioxide Levels of Inhaled and Exhaled Air - Limewater Test - 
Simple Science and Maths: 
{{youtube>O1d9dmNnnks?}}\\

📄 Experiments to compare carbon dioxide content of  inhaled and exhaled air - Bio Topics: [[https://www.biotopics.co.uk/humans/inhaledexhaled.html]]\\

====Variations====
  *Collect exhaled air in a bag and pass it into the liquid instead of breathing directly.  
  *Compare results for resting breathing versus after exercise.  




====Safety Precautions====
  *Do not inhale directly from containers with chemicals—only breathe through the mouthpiece setup.  
  *Use fresh, clean mouthpieces for each participant to avoid sharing germs.  
  *Limewater (calcium hydroxide solution) can irritate skin and eyes—handle carefully and wash spills immediately.




====Questions to Consider====
  *What changes are observed in limewater with exhaled air? (It turns cloudy, showing CO2 is present.)  
  *Why must the same volume of air pass through each tube? (For a fair comparison of CO2 levels in inhaled vs. exhaled air.)  
  *What is the approximate CO2 content of inhaled vs. exhaled air? (Inhaled air ~0.04%, exhaled air ~4%.)  
  *How does this experiment demonstrate the role of respiration in humans? (It shows oxygen is taken in and carbon dioxide is released during breathing.)