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Everest—The Death Zone

Classroom Activity

Objective
To determine the concentration of oxygen in the air.

• copy of "The O² Factor" student handout (PDF or HTML)
• small piece of plain steel wool (without soap or oil)
• 2 test tubes
• 2 beakers
• 2 burette clamps
• 100 ml graduated cylinder
• pencil
• masking tape
• water

1. The amount of oxygen in the air at high altitudes is much less than at sea level. As a result, oxygen deprivation, or hypoxia, is one of the greatest threats high altitude climbers face. Students can determine the concentration of oxygen in air at their location in this activity. Divide the class into teams and distribute the materials and activity sheet.

2. Start by asking students to predict how much of the air is oxygen. Then have them determine the volume of oxygen in air within a test tube by removing the oxygen through the oxidation of steel wool (plain steel wool is available at most hardware stores). Make sure that students understand that as the steel wool rusts, it is using oxygen.

3. Familiarize yourself with the formula you will use with students to calculate the amount of oxygen with Calculating the Percentage of Oxygen in the Air in Activity Answer below. How do students' results compare with their predictions? Note that air is about one-fifth oxygen. Have students explain why their results might differ. Then have them estimate the amount of oxygen they think is at the summit of Mt. Everest and defend their reasoning.

4. Conclude with a discussion of the difference in oxygen levels and reasons why.

Prior to the activity, students should understand that as steel wool rusts, it is using oxygen. Another term for rusting is oxidation. As steel wool undergoes oxidation, the iron molecules in the steel wool combine with oxygen in the air to form a new compound, iron oxide, or rust.

The steel wool should be wet or it will not rust. As the steel wool begins to rust inside the test tube, the water level in the tube rises to displace the oxygen used in the oxidation process. The water is pushed up by the air above the surface of the water in the beaker. The steel wool stops rusting when there is no more oxygen available in the air sample, or when the steel wool is completely used up. Students should observe that the rusting process stops at the same time that the water level stops changing. As a control, the water level in the test tube without steel wool should remain approximately the same. The rusting process will usually stop after one day, but students can observe over several days to confirm that the water level is no longer changing.

Oxygen makes up about one-fifth, or approximately 21 percent, of air. While the percentage of oxygen in the air remains the same at sea level and on the summit of Mt. Everest, oxygen is less concentrated at high altitudes because of the pressure differential, thus making it more difficult for climbers to get the amount of oxygen they need.

Most climbers who attempt to summit Everest bring supplemental oxygen with them to aid their breathing. Lack of oxygen can cause many stresses to the body, including obvious symptoms like gasping for breath, as well as more subtle symptoms like lack of ability to retain body temperature, loss of appetite, difficulty making decisions and thinking clearly, and fatigue.

Calculating the Percentage of Oxygen in the Air
To find the volume of oxygen in the test tube with the steel wool, have students compare the original volume of air to the final volume of air. To find the original volume of air, have them fill the test tube to the first mark with water and measure the volume in a graduated cylinder. To find the final volume of air, have students fill the test tube to the final mark and measure. Subtract the final volume from the original volume to find the volume of oxygen. Divide this number by the original volume and multiply that ratio by 100 to get the percent of oxygen in the air.