How Much Oxygen Is in the Air?

Grade Levels: 5 - 10

When you step outside and take a big breath of fresh air, do you have any idea what you're breathing in? The atmosphere is made up of a variety of gases, including nitrogen, oxygen, argon, carbon dioxide, neon, helium, methane, and so on. The primary ingredient is nitrogen, followed by oxygen.

You can do your own test of how much oxygen is in the air by making a controlled environment and using a common material to pull the oxygen out of the air. You'll need some of those hand-warmer pouches that outdoorsy types use in the winter. You can find them at sporting goods or hardware stores, and they're generally inexpensive.

The hand warmer pouches contain various materials that are sealed in plastic. When the materials are shaken together and exposed to the air, which occurs when you open the package, they react with one another and begin to oxidize. The oxidation causes heat. Some popular brands of hand warmers are Hot Rods and Heat Factory.

Fasten a pouch to the inside bottom of a tall, straight glass. You can do this with heavy tape. Then invert the glass onto a shallow plate that contains water.

What will happen is that the materials contained within the hand warmer will deplete the oxygen inside the glass. The other stuff-the nitrogen, carbon dioxide, argon, and so forth-will stay in there, and the oxygen will be replaced with water that will rise from the plate. You'll be able to tell how much oxygen was in the glass by the percentage of water it contains after all the oxygen is used up.

The simple science behind this experiment is that the hand warmers function due to a chemical reaction. The pouches contain iron, which, when exposed to oxygen, oxidizes and makes heat. When the iron oxidizes-or rusts-it devours the oxygen in the air. You can mess around with this idea and perhaps come up with an alternative you like better.

The project suggested here, however, is interesting and fairly dramatic without being very difficult to put together.

Excerpted from The Complete Idiot's Guide to Science Fair Projects © 2003 by Nancy K. O'Leary and Susan Shelly. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

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