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Name: Sally
Status: student
Grade: K-3
Location: IN
Date: April 2008

Question:
Can you do a experiment that tells you how much oxygen is in the air?



Replies:
Yes.

Get a clean glass jar and put a wad of steel wool inside on the bottom. Make sure you stuff it in the jar so it does not fall out when you turn the jar upside down. You might get an adult to help you with this.

Fill a flat bottomed bowl or dish half full of water and let that stand for a day or two. The water in the bowl must go half way up the outside of the bottle when you put it in the bowl.

Put the jar, upside down into the water like the diagram. Put some pebbles under the jar so water can get in easily. The water will come up into the jar a little. Mark the level of the water in the jar with a grease pencil.

Check the set up each day. The steel wool will rust and water will rise up into the jar. When you are sure that the water is not coming up any more, mark the level of the water inside the jar. The difference between the two marks is how much oxygen was in the air in the jar.

The rust is combination of steel (iron, actually) and oxygen. The rust that forms, uses up all the oxygen in the jar. The water flows in to take the place of the oxygen.

        -----------
  Jar   |#########|    #### = steel wool
        |#########|
        |         |
        |         |
|       |         |     |
|.......................|  water level in bowl at start of
|       |         |     | experiment
|       |         |     |
|       |         |     |
|       @        @      | pebbles keep jar of bottom of
|_______________________|  bowl


Have fun!

Robert Avakian


Sally,

Good question Sally. While there are many ways to do this, a simple way is to weigh a candle. Then we can light the candle and immediately put it inside a very large sealed container. The candle will continue to burn until there is no more oxygen inside the very large sealed container. So we wait for the candle to stop burning. When the candle stops burning, we weigh it again. The candle will now be lighter in weight because some of it reacted with the oxygen in order to burn. Since we know how much weight of the candle was lost in the burning process, and we know exactly what kind of chemical reaction happened between the candle and the oxygen, we can calculate how much oxygen was in the sealed container. If we know the size of the container, we can calculate how much oxygen there is for a particular volume of air (the volume of the container).

Greg (Roberto Gregorius)


There are lots of experiments scientists can run to measure the oxygen in the air. There are sensors that directly measure oxygen. There are chemical reactions that depend on oxygen (you can tell the amount of oxygen from the rate of the reaction). You can even tell something about oxygen levels in history my looking at certain kinds of rocks or ice or other things.

Typically, about 1/5 of the air around you is oxygen. If you want to know if there is oxygen, one easy way is to burn something. If there is no oxygen it will not burn (try lighting a match and putting it in an air-tight container (like an upside-down glass). The match will go out a lot faster than a match out in the open air. It is a little harder to tell *how much* oxygen is in the air without specialized equipment or complicated methods.

Also, make sure you have parental or teacher supervision before trying any experiments. BE VERY CAREFUL when lighting matches or doing anything with fire. Also, *you* need oxygen to live -- do not try things that change the amount of oxygen around *you*.

I hope this helps,

Burr Zimmerman



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