Nothing to Sniff At
You and Your Students!
Vicki Cobb, Education World Science Editor
Two amazing experiments teach students about breathing.
Setting the Scene (Background)
I love to challenge students to take a closer look at phenomena that we don't think about much. Breathing is one of those things we take for granted, so long as our noses are clear and there is plenty of air. You probably know that the air you breathe out contains more carbon dioxide than the air you breathe in. In this activity, I give you a way to show that.
By the way...
The first activity below can be performed by students. The second experiment can be done as a demonstration.
Here's a little-known fact about breathing: Did you know that your nostrils take turns taking in air? In this activity, each child will need a small pocket mirror (you can find them at most dollar stores). Have children hold their mirrors horizontally just above their upper lips. They should breathe down gently once and then look at the mirror. The moist breath will cloud up the mirror making an area of condensation for each nostril. Amazingly, one area will be larger than the other, indicating that more air is coming out of one nostril than the other. If you repeat this exercise in several hours you will find that the nostrils have reversed themselves.
Air provides our bodies with oxygen. We use air to live, and that produces waste products. Carbon dioxide is our "waste gas," and we get rid of it when we breathe out. Carbon dioxide dissolves in water to produce a weak acid (a sour solution).
We can "see" the presence of acids by using certain chemicals, called indicators. Indicators change color in the presence of acids. One of my favorite and easy-to-get indicators is red cabbage juice.
To make red cabbage juice, chop up some red cabbage, or purchase a bag of chopped-up red cabbage in your supermarket's produce section. Put about a cup of it in an enamel (not aluminum) pot and cover with water. Boil for a few minutes -- until the cooking water is purple. Strain the purple water (cabbage juice) into a clear glass.
Note: You can prepare the cabbage juice at home the night before doing this experiment for students.
Pour half of the cabbage juice into another glass and have a child use a straw to blow bubbles into it. After a few minutes, the purple water will be pink. That's the effect that adding an acid (carbon dioxide from the breath you are blowing into the water) has on an indicator.
If you put in an alkali (a "base" solution, the opposite of an acid) into the purple water, it will turn green. You can demonstrate that by adding any base -- baking soda, for example -- to your indicator.
Behind the Scenes
The nose is like a little computer. Each nostril takes a turn every few hours being the dominant nostril.
Carbon dioxide makes up 0.038% of the air we breathe in. It comprises about 4.5% of our exhaled breath. To prove that exhaled breath contains more carbon dioxide than air, you might bubble air through another sample of cabbage juice water using an aquarium aerator. It should produce no color change.
Article By Vicki Cobb
Copyright © 2009 Education World
Originally published 12/08/2005
Last updated 02/07/2009