Measuring Atmospheric Oxygen
Date: April 2008
Can you do a experiment that tells you how much oxygen is
in the air?
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
Jar |#########| #### = steel wool
| | | |
|.......................| water level in bowl at start of
| | | | experiment
| | | |
| | | |
| @ @ | pebbles keep jar of bottom of
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
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,
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Update: June 2012