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DETECTING THE PRESENCE OF OXYGEN

Other than the fact that we are still breathing and alive, how can we tell whether or not oxygen is present?

There are two tests for the presence of oxygen in this project, but since one of them involves fire, we will discuss only one.

Does anybody know what rust really is? It is a chemical reaction that occurs when oxygen and iron meet. It is a form of burning! That piece of information was a surprise to this writer.

I have always believed that iron would rust if it got wet, and did not know that iron does not need water in order to rust. Perhaps when iron gets wet, the water removes any coating on the iron, exposing it to oxygen, and THEN it would rust. We'll have to look into this further.

Anyway, we can prepare some steel wool (which is really iron) so that it will tell us whether or not there is oxygen.

Let's put on our plastic gloves, to protect us from slivers. Then we can take out one roll of steel wool from the box, find its loose ends, and unroll it. After we use scissors to cut off the knotted end, we can divide the roll into about 16 pieces, and roll each piece into a loose ball about 3/4 inch in diameter.

The steel wool balls have to be soaked in white vinegar until tomorrow, so as to remove the coating that protects them from rusting. In the morning, we will rinse them with tap water.

Push a ball of wet steel wool into the bottom of a test tube or some other gas-collecting container. Wedge the ball just tight enough to hold it in place when the tube is inverted.

Using yeast and 6% hydrogen peroxide (shown in Project Number C131.15), produce and collect some oxygen.

Fill the test tube containing the ball of steel wool with water, and invert it in the dish. Place the free end of the rubber tubing into the test tube. Leave the inverted test tube in the water for forty-eight hours.

If the steel wool rusts, oxygen must have been present in the test tube.

[An estimate of the amount of oxygen entering the test tube can be made by measuring how much water moved into the dish and subtracting this volume from the total volume of the test tube.]

If oxygen can be collected like this in three or four identical test tubes or other collecting containers, you can do experiments to answer a number of questions which naturally arise from this test.

1. For example, if you think that the distance between the steel wool and the water made a difference in the rise of the water, put a steel wool ball in the base of one container, three-fourths of the way down in another, halfway in a third, and one-fourth of the way in a fourth.

Leave the containers of water inverted in the dish for forty-eight hours and collect gas in them just as before. Now observe the water levels in the containers.

2. If you want to know if two steel wool balls would cause the water to rise higher than one steel wool ball would, place two balls in two containers and one ball in each of two other containers. Observe the results after forty-eight hours.

Now we need to know if iron needs to be wet in order to rust (for a reason besides removing any protective coating).


 
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