30 1. The limewater given initially in the test tubes was clear and transparent. When you blew on this limewater, it turned milky. Limewater turns milky when there is more carbon dioxide than is normal in the air around us. The limewater in the test tube turned milky when you blew on it. This indicates that the air we exhale has more carbon dioxide than the air we inhale. 2. When we left the test tube alone for some time, its milky nature disappeared. This is because there is a lower level of carbon dioxide in the air around us. Limewater turns clear when it is placed in lower levels of carbon dioxide. 3. When we blow on the mirror, we see that the mirror becomes cloudy and moist. 4. When we blow into our hands, the air feels warm and wet. Both these observations indicate that there is a higher level of moisture in the air that we exhale than in the air around us. Also, the air that we breathe out is at a higher temperature than inhaled air. 5. Since the exhaled air is warm and moist, some people blow on their glasses to clean them. The small amount of hot water in our exhaled breath helps to clean the glasses better. We have seen that the air we breathe in is changed in our bodies. The air that we breathe out has more carbon dioxide and moisture and is at a higher temperature than inhaled air. 6. Air is a mixture of gases – mainly nitrogen, oxygen, carbon dioxide and water vapour. The largest component of air is the inert gas, Nitrogen. From the chart showing the composition of inhaled and exhaled air, we can see that exhaled air is clearly different from inhaled air. While inhaled air has 20 to 20% of oxygen in it, exhaled air has only 15 to 16% of oxygen. This shows that around 25% of inhaled oxygen is used up by our body. The percentage of carbon dioxide in air is very low. However, this percentage increases by nearly 100 times in exhaled air (4%) in comparison with inhaled air (0.03 to 0.04%). Water vapour content in the atmosphere constantly changes, and so no numbers are given for it in the chart. However, the air that we breathe out has more water vapour and is warmer than the air around us.
KEY MESSAGES
The air we exhale is different from the air we inhale, because it is changed within our bodies. Exhaled air has less oxygen, more carbon dioxide and moisture and higher temperature than inhaled air. The relatively high level of carbon dioxide in exhaled air can be verified by the lime test.
LEARNING CHECK Why did milky limewater turn clear when kept in air? (Ans: Air has a lower level of carbon dioxide than our exhaled breath. Since limewater remains milky only at high levels of carbon dioxide, it become clear when kept in air.)
TRY IT YOURSELF You can improve your lung capacity by doing breathing exercises and exercise. Exercise regularly and see whether you feel less breathless with time. Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies or mistakes to handbooks.agastya@gmail.com