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Compare the Contents of Inhaled and Exhaled air

In this worksheet, students will explain the main differences between inhaled and exhaled air.

Worksheet Overview





Everyone knows that we breathe in oxygen and breathe out carbon dioxide. But that's not technically true. The truth is we breathe in air and breathe out air... so what's the difference?


Inhaled Air


So, we need oxygen to live, but do you know how much of the air is made up of oxygen? 80%? 75%? ....it actually only makes up about 21% of the air.  


So what else is in there?


The air that is all around us is made up of mostly nitrogen, about 78% nitrogen in fact. So what about the other 1%? ...The other 1% is made up of 0.04% carbon dioxide, some water vapour and other gases such as argon, helium and neon.  


Pie chart of gases of the air


Exhaled Air

The reason we breathe is to get oxygen into our bodies to allow for respiration, so you would think that the air we breathe out would have a lot less oxygen right? Well, there is less oxygen in exhaled air but probably a bit more than you would expect. Exhaled air actually contains around 16% oxygen which means we only use about 5% of the oxygen available!


The percentage of nitrogen stays at nearly 78% (as we do not have any use for nitrogen) but the main difference is the increase in carbon dioxide. The carbon dioxide in exhaled air is more-or-less 4% and the percentage of water vapour is also higher than in inhaled air.  


 Pie chart of gases of the air


Experiment Time

There is a very simple experiment that we can do to prove that exhaled air contains more carbon dioxide than inhaled air.

Carbon dioxide will turn colourless limewater milky/cloudy.  


Blowing into limewater


The carbon dioxide percentage in inhaled air is so small that it doesn't have an effect on the limewater, however bubble some exhaled air through it and it will turn milky/cloudy. 


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