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ATMOSPHERIC COMPOSITION

Modeling Atmospheric Composition and Reactions in the Classroom

Authors
Gerald Saunders
Coolidge High School
Washington, D.C.
Carolinska@hotmail.com
Bevon Thompson
Benjamin Banneker Academy
Brooklyn, NY
Bevon1@hotmail.com

 

TABLE OF CONTENTS
Atmosphere: Chemical Composition and Structure
Time Required and Target Audience
Student Activities/Labs: Creating Model of the Atmosphere
Measuring the Percent of Oxygen in the Air 
 
Procedure 1
Suggested Questions
 
Rates of Heating and Evaporation in A Carbon Dioxide/Nitrogen 
Atmosphere 
 
Procedure 1 (creating the carbon dioxide/ nitrogen environment)
Procedure 2 (preparing the control, a oxygen/nitrogen environment)
Procedure 3  (rate of heating in a carbon dioxide/nitrogen environment)
Suggested Questions
 
References
National Science Standards
Suggestions and Comments
Relevant Links
 
 

THE ATMOSPHERE:   CHEMICAL COMPOSITION AND STRUCTURE

The Origin of the Atmosphere

The origin of earth's atmosphere is still a matter of speculation.  However, most scientists believe, based on their knowledge of the gases in the universe, the earth's first atmosphere was composed of helium, hydrogen, ammonia and methane.  Others believe that the first atmosphere was probably released gases from volcanoes venting the earth's hot inner core including N2, CO2, H2, CO, and H20.  The earth's second atmosphere can be traced to the planet's heating and differentiation.  It  probably consisted of the same gases that are released from volcanoes today: carbon dioxide, nitrogen, water vapor, and hydrogen and other trace gasses.   Planetary differentiation caused the lighter elements to rise to the other layers of the earth and initiated the escape of the lighter gases from the planet's interior.  The lighter gases eventually formed  the atmosphere and the oceans.

Chemical Composition of the Atmosphere

The atmosphere is a mixture of solids, liquids and gases.  The gases in the atmosphere are classified as either permanent (concentration remains constant) or variable (concentration varies with time).  The permanent gases include oxygen, nitrogen, neon, argon,  helium and hydrogen.  The most abundant of these permanent gas are nitrogen (78%) and oxygen( 21%).   The remainder of the permanent gasses and the variable gases exist in small concentrations in the atmosphere.  They are referred to as trace gasses.  The atmosphere also includes sulfur, chloroflorocarbons, dust and ice particles.

Important Atmospheric Gasses

Nitrogen

Nitrogen is also the most abundant gas in the atmosphere.  A large amount of nitrogen enters the atmosphere through volcanic eruptions, burning of biomass and denitrification.  Nitrogen is removed from the atmosphere and deposited on the earth's surface by nitrogen fixing bacteria and lighting.  The nitrogen in the soil serves as an important nutrient for plants.

Oxygen

Oxygen is the second most abundant gas in the atmosphere.  It is a diatomic molecule that enters the atmosphere as the waste product of the photosynthetic activity.  During photosynthesis carbon dioxide and water react, with the aid of sunlight, to form glucose and oxygen.  Oxygen is consumed during the process of respiration.  Oxygen is chemically combined with glucose to produce ATP along with carbon dioxide and water as a waste products.

Water Vapor

Water vapor is the most important natural greenhouse gas.  A greenhouse gas traps the infrared radiation that comes from the sun.  The trapped infrared radiation warms up the earth. This phenomenon is called the greenhouse effect.   Water vapor also redistributes energy in the atmosphere.  Water vapor is removed from the atmosphere during precipitation and returns by evapotranspiration.  The concentration of the water vapor varies in the atmosphere depending on the place and time of year.  The concentration of water vapor is greatest over the oceans and tropical rain forest.

Carbon Dioxide

Carbon dioxide is the fifth most abundant gas in the atmosphere.  Carbon dioxide enters the atmosphere during volcanic eruption, biomass and fossil fuel combustion, cement manufacturing and deforestation.  Carbon dioxide is removed from the atmosphere during  photosynthesis and by dissolving in the oceans.  In the oceans, some of the carbon dioxide reacts with water to form carbonic acid.  The concentration of carbon dioxide has increased 25% in the last 300 hundred years (see graph below).

[Atmospheric Concentration of Carbon Dioxide]

 
 

Ozone

Ozone is a natural component of the atmosphere.  It consists of 3 atoms of oxygen.  Ozone is an unstable molecule which readily breaks down into molecular oxygen and 1 other atom.  Ozone at high altitudes protects the biosphere from harmful ultraviolet radiation, a known hazard to plants, animals, (including  man).  Harmful effects of ozone depletion to humans include risks of skin cancer, cataracts, and adverse effects on the immune system.  At low level altitudes, ozone has a different effect,  It can cause respiratory problems (smog is largely made up of ozone gas) and it is corrosive and reactive with building materials.  Recently, ozone has been designated as a greenhouse gas.

03---------> 02 + 0

 

Time Required and Target Audience:  These activities were design for high school students but can be modified for middle school students.  Three 45 minutes class periods are required to complete the experiments.  This time does not include prep time and pre and post lab discussions.

Student Activities/Labs:Creating Models of the Atmosphere

Measuring the Percent of Oxygen in the Air

adapted from Baker, Richard Thomas, 1993. Weather in the Lab: Simulate Nature's Phenomena. Blue Ridge Summit, PA. Pages 71-73

Without oxygen there would be no human life on earth. In fact, there would be no animal or plant species. In fact, there would be no life except for those species that can exist without free oxygen, such as anaerobic bacteria.  Oxygen is an essential element that comprises 21% of the earth's atmosphere.  Oxygen reacts with many other elements to form compounds that are essential to many ecosystems.

C + 02  ------->  C02

 
Of course this reaction is the starting point for photosynthesis, which is the model for production of  02 in the atmosphere.

In this experiment, iron is oxidized from ferric to ferrous oxide.  Oxidation is a chemical process that occurs from a loss of electrons resulting in a more positive state for an element or compound.  This is the basis of rusting, as oxygen, carbon dioxide, and water complexes with iron to yield the characteristic orange red color of the oxidized metal.

The amount of oxygen leaving the test tube can be measured.  It is equal to the volume of the amount of water that enters the tube as oxygen is displaced.  When this amount is compared to the volume (in percent) of the test tube, the percent of oxygen in the air can be determined.
                                                                            02
                                                                Fe+3------------> Fe+2   +    e-
 


The following activity corresponds to the following National Science Standards:  Unify Concepts and Process in Science,  Content A , Content D and Content B

Objective:

Materials

1 standard size piece of steel wool
1 large test tube
1 ring stand
1 ring clamp
1 medium sized bowl
2 cups of water

Procedure

Pour 2 cups of water in a medium sized bowl.  Place a damp medium sized piece of steel wool inside the bottom of the test tube.  Invert the test tube.  Position a ring stand close to the bowl so that the clamp attached to the ring stand will hold a large test tube in place just inside the level of the water in the bowl. (see figure TBA)   Measure the test tube to 2 significant digits in centimeters.  After three days, mark the meniscus of the water line with a black marker.  Remove the test tube from  the pan and the ring stand clamp.  Take out the steel wool.  Measure the distance from the mouthpiece of the test tube to the mark in centimeters.  Do the calculations and and record the data in Table 1 below.

Equations

Fe + O2 -----> Fe2O3
As the oxygen inside the test tube is replaced with water due to the oxidation of the iron, water will begin to rise inside the test tube.   It is possible to determine the amount of water volume and translate it into an equation that approximates the amount of O2 in the atmosphere.

Measuring Oxygen Data Table

  1. Length of test tube (base to lip)________________cm

  2. Height of H20 after three days________________cm

  3. Ratio of water height to test tube length ______
    (For instance if the water rose 5 cm in 3 days and the height of the test tube is 15 cm, the ratio would be 5/15 cm or 1/3 or .33)

  4. Percent of space filled with water (3 x 100)________%
    (The ratio number times 100 gives you the percent of air in the test tube)

  5. Actual percentage of oxygen in air 20.946%

    6. Percent Error = (Difference between the Accepted and Experimental Value/Accepted Value) X 100%


Suggested Questions

Rates of Heating and Evaporation in a Carbon Dioxide/Nitrogen Atmosphere

adapted from: Baker, Thomas Richard, 1994. Two Sun And a Green Sky: 22 Out-of-This-World Weather Models and Experiments TAB Books, NY. Pages 54-56

Second only to water vapor, carbon dioxide is the most important greenhouse gas.  It has increased from 280 ppm in the 1800's to 360 ppm currently.  It is expected to rise to well over 600 ppm in the next 50 years, according to several models.  Carbon dioxide has a warming effect on the earth's environment. Carbon is the primary component of fossil fuels.  When they are burned, carbon is released into the atmosphere as carbon dioxide.  The oceans are a vast carbon sink with phytoplankton as its primary storehouse.  Global warming could offset the balance of the carbon cycle and cause increased carbon dioxide production. Carbon dioxide absorbs infrared radiation from the sun and prevents it from returning to space.  As a result, there is a significant increase in the temperature of the atmosphere of the earth.   What would happen to the rate of evaporation and condensation on earth if its atmosphere was made solely of carbon dioxide and nitrogen?  Would the rate of heating and cooling of the atmosphere change?  Would the pH of the water on the planet change?  Write one or several hypotheses to answer the previous questions.  Use the procedure below to set up a model atmopshere to test your hypothesis.

Note: You must complete Procedures 1 and 2 in this section in order to begin the experiment.

The following activity corresponds to the following National Science Standards:  Unify Concepts and Process in Science,  Content A,  and Content D

Objectives

Materials

aquarium
glass cover
masking tape
1 tea candle
1 shallow pan
tap water
1 alcohol thermometer
1 100 watt white lamp
1 lamp shield
1 ring stand with clamp
centimeter ruler
goggles
1 250 Erlenmeyer flask
 

Procedure 1: Creating the CO2/  Nitrogen Environment

Safety Precaution: Always wear goggles near an open flame.  Wear gloves when handling all chemicals, particularly toxic substances. Review safety manual provided by the American Chemical Society or your Chemistry lab manual.

  1. Make a copy of the data table
  2. Set the lamp 25 cm away from the top of the aquarium (any closer and the glass could crack).
  3. Fill a shallow pan or tray with 2.0 cm of room temperature tap water.
  4. Accurately measure the depth of this water on a level surface with a ruler.
  5. Place the pan inside the tank.
  6. Light the candle inside the tank.
  7. Place the heating screens over the candle.
  8. Turn the lamp on to begin  heating.
  9. Write down the beginning temperature.
  10. Seal the lid to the tank with masking tape.
  11. Heat the tank for 24 hours.
  12. Large drops of water vapor should form on the sides of the container.
  13. Record the ending temperature.
  14. Turn off the lamp.
  15. Carefully remove the masking tape strips from the glass cover.  Open the aquarium.  Carefully remove the pan or tray.
  16. Set the pan on a level surface.  Accurately measure the depth of the remaining water.
  17. Record this final height of water.
  18. Calculate the amount of evaporation.
  19. Record the data.
  20. Pour out the condensed water inside the tank and dry it thoroughly.

Procedure 2: Preparing the Control (Oxygen/Nitrogen Atmosphere).

  1. Set the lamp 25 cm away from the top of the aquarium (any closer and the glass could crack).
  2. Fill a shallow pan or tray with 2.0 cm of room temperature tap water.
  3. Accurately measure the depth of this water on a level surface with a ruler.
  4. Place the pan inside the tank.
  5. Turn the lamp on to begin heating.
  6. Write down the beginning temperature.
  7. Seal the lid to the tank with masking tape.
  8. Heat the tank for 24 hours.
  9. Large drops of water vapor should form on the sides of the container.
  10. Record the ending temperature.
  11. Turn off the lamp.
  12. Carefully remove the masking tape strips from the glass cover.  Open the aquarium.  Carefully remove the pan or tray.
  13. Set the pan on a level surface.  Accurately measure the depth of the remaining water.
  14. Record this final height of water.
  15. Calculate the amount of evaporation.
  16. Compare to previously data recorded in Procedure 1.
  17. Pour out the condensed water inside the tank and dry it thoroughly.

Oxygen/Nitrogen Data Table

 
Beginning Temp.
Ending Temp.
Initial Height of H2O
Final Height of H20
Amount of Evaporation
(oC)
(oC)
(A)
(B)
(A-B)
   
2.0 cm
    
         
         
 

 

CO2/Nitrogen Atmosphere Data Table
 
 
Beginning Temp.
Ending Temp.
Initial Height of H2O
Final Height of H20
Amount of Evaporation
(oC)
(oC)
(A)
(B)
(A-B)
   
2.0 cm
    
         
         

Rate of Heating.

Procedure 3: Preparing Atmosphere for Rates of Heating Experiment

Use procedure 1 above to create a carbon dioxide/nitrogen environment and an oxygen/nitrogen environment as a control.  Be sure to seal the tank with a thermometer taped to the side.  Allow the tanks containing the candle to cool for 15 minutes.  Record the temperature of the individual tanks. Place the lamp on the tanks and record the temperature every 15 minutes for 90 minutes.  Generate an hypothesis to explain what you believe might happen.

Rate of Heating Data Table

Oxygen/Nitrogen Time (min) /  Temperatures (o C)

 CO2/Nitrogen Time (min) /Temperatures (o C)
15 min/ 15 min/
30 min/ 30 min/
45 min/ 45 min/
60 min/ 60 min/
75 min/ 75 min/
90 min/ 90 min/
 

Suggested Questions:

Rate of Heating

 

References

Websites

Suggestions and Comments: Please email us your input on the web site so that we may improve it.

Relevant Links:

Atmospheric Chemistry and Dynamic Branch Research
Climatalogy and Paleoclimatology Resources
Atmospheric Composition
Woodrow Wilson Fellowship Foundation
Greenland Observatory
Environmental Protection Agency
Danger in the Air: What is in Our Air
Global Warming

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