Percentage of Oxygen in the Atmosphere



Percentage of Oxygen in the Atmosphere

Purpose: to determine the %Oxygen in the Earth’s atmosphere

Procedure:

1. Light the candle and let a few drops of wax drip on the penny and quickly place the candle on the drops before they dry.

2. Fill the large test tube with water, completely. Pour the water into a graduated cylinder and measure the volume. This volume of water is the same as the volume of air in the test tube. Record it as “volume of air at the start” Dry the test tube.

3. Pour the water into a 400mL beaker. Carefully place the penny and candle in the center of the beaker, making sure not to the wick wet.

4. Carefully, light the candle, and rapidly invert the same large test tube over the lighted candle. The test tube has to be IN the water, BUT NOT TOUCHING THE BOTTOM OF THE BEAKER.

5. As the candle uses oxygen in the test tube, the flame goes out and water will be drawn up into the test tube to replace the oxygen. Do NOT MOVE THE TEST TUBE.

6. Carefully, mark the level on the test tube where the water rises to with a marker or black crayon. Once this mark is made, you can lift the test tube. Try not to get the candle wet so you can do a trial 2.

7. Fill the test tube to the level that you marked. Pour that water into the graduated cylinder and record the volume as “volume of air after the candle goes out”.

8. To find the volume of oxygen originally in the test tube, subtract volume of air after the candle goes out from volume of air at the start. Record as volume of oxygen in the data table.

9. To determine the percentage of oxygen in the air, use the formula below:

%Oxygen =(volume oxygen / volume of air in test tube at the start) X 100

Record your answer in the data table.

Data Table:

Volume air at the start

Volume air after the candle goes out

Volume of oxygen

Percentage of oxygen in the air

Questions:

1. Would the same result for the percentage of oxygen in the air be obtained if a larger test tube was used? Why or Why not?

2. Why does the water rise into the test tube as the candle goes out?

3. If water rises in the test tube to replace the oxygen used up by the candle, what is the air left in the test tube composed of?

The percentage of oxygen in Earth’s atmosphere should be 21%...calculate your percent error.

%error= (21-(your percent) / (your percent) ) X 100

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