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# How Much Oxygen is in the Air?

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### Research Question:

How much oxygen is in the air?

How much oxygen is in the air? This experiment will help you find out. You will create rust, and then make use of the fact that rust and oxygen interact with each other chemically to determine what percentage of the air in a tube was made up of oxygen.

### Materials:

• Glass jar
• White vinegar
• Pad of soap-free fine steel wool
• Wide, shallow bowl or pan
• Water
• Food coloring
• Plastic or rubber gloves
• Four test tubes
• Permanent marker

### Experimental Procedure:

1. Fill the jar with an equal volume of white vinegar and water.
2. Place the pad of steel wool in the jar, and leave it there overnight to soak. This will form iron oxide (rust) on the steel.
3. Pour about an inch of water into the bottle of a shallow bowl. Add two drops of food coloring to the bowl.
4. While wearing gloves, pull several strands of the steel wool from the rusted pad, and roll them together to make a small ball. Repeat this process two more times so that you have three small balls. The balls should be slightly wider than the test tubes.
5. Use a pencil to push one ball all the way to the end of one of the test tubes, one ball three quarters to the end of a second test tube, and one ball halfway into a third test tube.
6. Crumple up a small ball of paper to the same size as the balls of steel wool, and push it all the way into the fourth tube.
7. Place the four tubes upside down in a row in the shallow dish of prepared water. Leave them there for 24 hours.
8. Mark the water level on each tube. Observe the differences in water level. The tube with the paper in it should not have risen at all. Now measure the length of each tube, assuming that the bottom of the steel ball marks the top of the tube. Insert both of these measurements into a chart such as the one below.

Tube Number Heigh of Water Heigh of Test Tube Percent of Oxygen in Test Tube
1
2
3
4
9. Fill in the fourth column of the chart by dividing the height the water rose by the height of the test tube. Keep in mind that the water that moved up the tube was replacing the oxygen that reacted with the rust. The ratio of the three test tubes should be the same, since it is the same as the percentage of oxygen in the air, or about 21%.

Terms/Concepts: Chemical reaction; How do vinegar and steel make rust?; How do rust and oxygen interact chemically?

References:

• Easy Genius Science Projects with Chemistry, by Robert Gardener, pp 73-76.
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