Bringing The Greenhouse Effect Down To Earth
Grade Level: 9-12
To compare the amount of Carbon Dioxide (CO2) in four
different sources of gases.
(Enough for each team of two or four students)
5 vials or test tubes
A graduated cylinder
A funnel straw
A marble-size piece of modeling clay
4 different colored balloons
A narrow-necked bottle (the neck should be narrow enough for a
balloon to fit over it)
A dropping bottle of bromthymol blue indicator solution
A dropping bottle of dilute household ammonia (1 part ammonia
to 50 parts distilled water)
100 mL vinegar
5 mL baking soda
Safety goggles for wear at all times
Teacher's Lab Notes:
The students will be filling balloons with pure carbon dioxide,
exhaled air, and ambient air. For safety reasons, you should
fill the balloons with automobile exhaust. You should wear thick
gloves to protect your hands from being burned. Fill the balloons
in an open area and when a slight breeze is
blowing to keep the exhaust gases away from your face. Place a
balloon over the narrow end of a metal funnel and place the wide end of
the funnel over the exhaust pipe of a running car. When
inflated, the balloons should be about 7.5 cm in diameter. It may
be easier to overinflate the balloon and then let a little
gas escape. Twist and tie the balloon. Repeat the procedure
with the same color balloon until you have one for each lab
The ambient air solution in vial A will not turn yellow.
The level of CO2 in ambient air is too low to affect
Students will need around 60 drops of the diluted ammonia
to neutralize the solution in vial D (vinegar-baking soda
reaction). The other two vials should require between 7 and 40 drops.
Caution students to add the drops slowly and shake
solutions between drops so they can get a careful record of when the
color changes back to the same color blue as the control.
Since the students will have to add a relatively large
amount of ammonia to the solution in vial D, the color of this
sample may be affected by dilution. To equalize this effect, you can
have students add some water to the other samples to make the
volume in each sample equal. This is easiest to do if sample D
is titrated last.
1. Add 15 mL of water and 10 drops of bromthymol blue
indicator solution to each vial or test tube. Label the vials A, B,
C, D, and Control.
2. Fill each balloon until it has a 7.5 diameter.
Sample A (Ambient Air) - Use a tire pump to inflate
balloon to the required diameter. Twist the rubber neck
balloon and fasten it shut with a twist tie. The tie
at least 1 cm from the opening of the balloon. Record the
of the balloon used for this sample.
Sample B (Human Exhalation) - Have one team member
blow up a
balloon to the required diameter. Twist and tie the
record balloon color.
Sample C (Automobile Exhaust) - Your teacher will
with this balloon. Record the color.
Sample D (Nearly pure CO2) - Put 100 mL of vinegar in
narrow-necked bottle. Using a funnel, add 5 mL of baking
Let the mixture bubble for 3 seconds to drive the air out,
slip the balloon over the neck of the bottle. Inflate the
balloon to the proper diameter. Twist, tie, and record
3. Soften the clay and wrap it around one end of the
straw to make a small airtight collar that will fit into the neck
of a balloon. The collar should look like a cone with the
straw in its middle, and should be large enough to plug the neck of
4. Pick up Balloon A. Keeping the tie on it, slip the
balloon's neck over the clay collar and hold it against the collar
to make an airtight seal. Place the other end of the straw into
the vial of water and bromthymol blue labelled A. Have another
partner remove the tie on the balloon and slowly untwist the
balloon. Keeping the neck of the balloon pinched to control the flow of
gas, gently squeeze the balloon so the gas slowly bubbles
through the solution.
5. Repeat the same procedure with the other balloons and
their respective vials. In some cases, the bromthymol blue
solution will change color, from blue to yellow, indicating the
presence of carbonic acid formed from CO2.
6. Analyze each of the samples by titrating them with
drops of dilute ammonia. Ammonia neutralizes the carbonic acid.
The bromthymol blue will return to a blue color when all the
acid has reacted. Add drops of ammonia to each of the samples that
turned yellow, carefully counting the number of drops needed
until they are about the same color as your control. Record the
Post Lab Discussion:
Make a chart on the board to pool each group's results.
Ask the students which samples had the most and the least carbon
dioxide. Why didn't the ambient air sample not turn yellow? (The
test isn't sensitive enough to detect low concentrations of
CO2.) Carbon dioxide is a natural part of our atmosphere, but
too much CO2 could make the Earth warmer through an increased
greenhouse effect. Why is automobile exhaust a concern? What ways
could you reduce the amount of CO2 you create? How could a city
reduce the amount of CO2 they emit? What's more important, to
develop and adapt cars with a new fuel that's safe for the
environment or to improve public transportation systems? What
alternative power sources could be used with cars? (Solar, electric,
methanol.) Why might it be difficult for the public to start using an
alternative source? (Car industry not mass-producing new
cars, expense of buying new car, less power/speed than gas-
This activity is used with the permission of Climate
Protection Institute. CTI publishes "Greenhouse Gazette" and other
programs. To receive more information about CTI and other
activities, write and tell them what grade you teach at
5833 Balmoral Dr., Oakland, CA 94619. This activity appeared in
The Science Teacher, May 1989.