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NOVA scienceNOW: Capturing Carbon
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Viewing Ideas
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Before Watching
Examine the structure of a leaf. Pair students and have them inspect leaves from
different plants and trees. Have them make drawings or rubbings, and describe
the shape and size of each leaf. Then ask them to research the parts of the
leaf and label their drawings. Discuss the advantages and disadvantages of
various shapes and sizes. (e.g. leaves have pointed tips to shed water, pine
needles are very narrow leaves which shed snow easily) Leaves are adapted to
their function and their environment, allowing optimum access
to sunlight, air, and water.
Discuss the role of a leaf in
photosynthesis, the process by which a plant turns light energy (sunlight) into
chemical energy (glucose or sugar). Below is a simplified version of the
photosynthesis equation:
carbon dioxide + water + light energy → carbohydrates (chemical energy) + oxygen + water
Focus on the role of carbon
dioxide. Air (which contains .05% carbon dioxide) enters the leaf through stomata
on the underside of its leaves. The location of the leaves on a plant, and
their shape, effects the amount of sunlight they absorb and how air flows
around the plant.
Extension 1: Germinate beans and allow them to grow to the two-
or four-leaf stage. Snip off the terminal bud which is actively growing. This
will limit the photosynthesis to the existing leaves. Using petroleum jelly,
coat the tops of all the leaves on one plant, and coat the undersides of all
the leaves on a second plant. Leave the third plant as is; it will serve as the
control. Place all three in a place where they receive sunlight, and water them
as you would normally, treating each plant the same. Observe the plants each
day for a week or more, noting their health and growth. (The control should
do well; the plant with the tops of the leaves coated should do nearly as well
as the control, and the plant with the underside of the leaves coated will wilt
and begin to die. Plants take in air, and thereby carbon dioxide, through
stomata on the undersides of their leaves; when the stomata are blocked by the
petroleum jelly, the plant does not get the CO2 it needs for photosynthesis and
will eventually die.)
Extension 2: Submerge a fresh-cut leaf (e.g., aquatic plant
leaf or geranium) in a container of water and place the container in bright
sunlight. After about one hour, have students examine what is happening on the
leaf's surface; a magnifying glass may help. Students should see tiny
bubbles on the leaf. The oxygen bubbles are a result of photosynthesis. Explore carbon dioxide. Discuss with students that carbon dioxide (CO2)
is a vital, though relatively small, part of Earth's atmosphere, with
concentrations of about 385 parts per million (.038%). It is a greenhouse gas,
contributing significantly to the heat-retaining capabilities of our
atmosphere. Carbon dioxide is also found in Earth's oceans, (dissolved in
seawater), at concentrations much higher than in the atmosphere.
It is used by plants as part of photosynthesis and produced by plants and
animals during respiration. It is also produced as a byproduct of burning
fossil fuels and during the decomposition of organic matter. It is used by
human beings for everything from carbonating soda to making plastics to putting
out fires. Carbon dioxide exists as a gas at normal room temperatures and
pressures, turns directly from a solid (dry ice) to a gas at very cold
temperatures (below -78°C ), dissolves in water and other liquids. Carbon dioxide can
exist in all three states and can be dissolved. This adaptability opens many avenues to sequestering it. (The only way to mitigate the
effects of carbon dioxide in the atmosphere is to sequester it. Sequestration is a process that traps atmospheric carbon
dioxide.)
Perform the demonstrations below and
ask students questions to encourage them to think about the properties of
carbon dioxide.
Safety
Warning: Wear goggles when handling the
materials below and during each demonstration.
Carbon
dioxide in seltzer: Demonstrate that water
can contain carbon dioxide by simply opening a fresh bottle of seltzer or
sparkling water. Gas bubbles will form in the water the instant you release the
pressure, because the high pressure inside the sealed bottle allows more carbon
dioxide to dissolve in the water than would dissolve at typical atmospheric
pressures. (Carbon dioxide can be stored in water under pressure.)
Extension: Calculate the amount of carbon dioxide in seltzer.
Place a bottle of seltzer water or soda on a scale and record its weight. Shake
the bottle, wait until the foam settles a bit, and then very slowly and
carefully open the cap, releasing the carbon dioxide while not spilling any of
the liquid. Repeat this until the bottle stops (or mostly stops) changing in
weight. (In general, there is about 2 grams of CO2 per 454
milliliters, or 16 ounces, of seltzer.) Carbon
dioxide from vinegar and baking soda:
Carefully pour about 2 tablespoons of vinegar into a plastic bottle and spoon
about 1 teaspoon of baking soda into a balloon. Stretch the mouth of the
balloon over the mouth of the bottle, being careful not to spill any of the
baking soda into the bottle. Lift the balloon so that the baking soda pours
into the bottle, and observe what happens. (Pressure will build so you may
want to keep one hand around the neck of the balloon where it is stretched over
the mouth of the bottle.) When the baking soda and vinegar come in
contact with each other, a chemical reaction occurs, and carbon dioxide is
produced, and the balloon inflates. Carbon
turns neutral water into acidic water:
Before class, prepare a solution of bromothymol blue (an acid-base indicator)
by adding several drops of bromothymol blue (available from pet stores) to a
small bottle of distilled water. In class, pour small amounts of this solution
into four or more separate glasses.
Glass
1: Add a known base, such as baking soda or ammonia. (Bromothymol blue is
blue in basic solutions.) Glass
2: Add water. (Bromothymol blue is also blue in neutral solutions.) Glass
3: Add a known acid, such as vinegar or lemon juice. (Bromothymol blue is
green and yellow in acidic solutions, with the color becoming more and more
yellow as the acidity increases.) Consider
using more than one acid to demonstrate this variability in color. Glass
4: Have a student blow GENTLY through a straw into the bromothymol blue, slowly
bubbling the solution, being very careful not to drink any of the solution. (Dissolved
CO2 forms carbonic acid, so the solution gradually turns to a
yellowish-green.)
Model the
greenhouse effect: The greenhouse effect
is a natural, vital part of how Earth maintains its temperature range. The
greenhouse gases in the atmosphere trap heat, forming a blanket around the
Earth. Since the mid-1850s, humans have continually added carbon dioxide, which
is a greenhouse gas, to the atmosphere. This extra carbon dioxide increases the
heat-holding capacity of the atmosphere, disrupting Earth's
temperature-management system. This disruption is often called global warming.
Scientists are trying to remove carbon dioxide from the atmosphere. To examine
carbon dioxide's ability to absorb heat, have the class do the experiment
below. Test this experiment before having students perform it.
Safety
Warning: Wear goggles, and have students
wear goggles, when performing the activities and handling the materials below.
Materials
- three thermometers
- three clear, sealable
plastic bags
- 2 teaspoons baking soda
- 2 tablespoons vinegar
- one beaker
- black paper
Procedure
Place a thermometer in
each plastic bag. Seal one of the bags
with as little air inside as possible. Seal a second bag with
as much air inside as possible. Hold the third bag
wide open so that it has as much air inside as possible and then carefully pour
extra CO2 into this bag from a beaker of baking soda and vinegar; Seal the third plastic
bag, containing as much CO2-rich air as possible. Record the temperature
measured by each of the thermometers. Place all three bags
on the black paper. Expose them to direct sunlight for 10 to 30 minutes.
(Consider watching the while the bags are being exposed to the sun. On a very
sunny day, the changes may be fast and some thermometers may reach their peak
temperature.) Check the thermometers
regularly, observing the changes in temperature. Discuss why each one is
different.
[When sunlight enters
Earth's atmosphere, some of that energy is absorbed (by the atmosphere
and by Earth's surface) and reradiated as heat. Some of this heat energy
escapes into space, but the greenhouse gases in Earth's atmosphere trap
much of it. Similarly, the gas in the bags traps heat energy, causing the
temperature to increase. Since CO2 is an important greenhouse gas,
the bag with additional CO2 usually traps more heat. (NOTE: As with
any demonstration, the results should, but do not necessarily, match those
expected. If the temperatures in the bags do not support the role of greenhouse
gases in heat capture, discuss the nature of scientific experimentation,
including the importance of multiple trials, control of conditions, and
measurement challenges.]
Extension: Observe the temperatures in the three plastic bags
after they have been removed from the sunlight. The same differences in
temperature that occur during heating can sometimes be observed while the bags
are cooling. The thermometer in the bag with little air will cool most rapidly,
without its "blanket" of trapped warm air, and the thermometer in
the bag with CO2-rich air will cool most slowly, with the extra
greenhouse gas helping to trap the heat inside the bag.
After Watching
Discuss global warming. There is strong scientific agreement that global
climate change is real and is largely due to human activities. For example, in
2004, the Washington Post printed an article titled, Undeniable Global
Warming, which reported that of 928 "global climate
change" abstracts published in scientific journals between 1993 and 2003,
75 percent accepted that are planet's climate is changing and humans are
partly responsible. The other 25 percent of the articles didn't disagree;
they simply dealt with specific aspects of global climate change and didn't
address whether or not humans play a role. Given this consensus, why is there
controversy?
Discuss
the topic of why global climate change and why the roles humans play in it are
so controversial. Discussion questions might include: What kinds of attitudes
and behaviors serve to keep things as they are? Why might business and industry
interests resist stricter rules, regulation, taxation, or public education
campaigns? Why might people resist changes that could reduce their own carbon
footprints? As appropriate, prompt them to discuss the following:
the importance of
fossil fuels in our daily lives, and the effects on our lives if we made
significant changes the economics of
gasoline, factories, cars, etc. the economics of
changing industries and infrastructure over to a new model the nature of
scientific knowledge and the difference between "global warming is an
absolute fact" and "based on the available evidence, Earth's
climate seems to be changing"
Calculate your carbon footprint. In recent years, people concerned about global
climate change and their role in that change have adopted the idea of a carbon
footprint, a measure of how much carbon
dioxide a person is responsible for putting into the environment. Some sources
of carbon dioxide considered in a carbon footprint are relatively direct, such
as driving a car to school or turning on the; even breathing! Other sources
sometimes considered are a bit farther removed, such as those that went into
the manufacture and shipping of products bought at the store, or even the bags
used to carry those items home. Once one understands his or her carbon
footprint and the factors that contribute to it, he or she may begin to make
changes to reduce it.
A
number of carbon footprint calculators are available on the Web, including one developed by the U.S. Environmental Protection
Agency. Have your students use this carbon calculator to calculate their own carbon footprints, and have them discuss the
many sources of carbon dioxide in their lives, as well as ways that they can
(realistically) make changes.
Perform experiments using limewater to learn
about carbon sequestration: In the
segment, Professor Klaus Lackner introduces the concept of carbon
sequestration, the storage of carbon in
the ocean, underground, and biosphere repositories. He then extends the idea to
another process, called mineral sequestration, which is the storage of carbon in serpentine rock
and similar mineral structures. According to Klaus, this process takes Mother
Nature hundreds of years. He and his graduate student Sam Krevor are working on
a way to shorten the time. However, you and your students can easily experiment
with binding carbon and forming rock. Specifically, you can demonstrate the
formation of limestone, or calcium carbonate, from the combination of carbon
dioxide and lime.
Safety
Warning: Wear goggles, and have students
wear goggles, when performing the activities and handling the materials below.
At least one day before class, gather
and prepare the necessary supplies:
- lime (also called
pickling lime or the chemical, calcium hydroxide)
- hot water (distilled
water works best)
- a spoon
- filter paper
- glass quart-sized
jars with lids
- glasses
- straws
Prepare the limewater:
Fill half of the jars with hot water. Add about 1 tablespoon of lime to each
jar (or 1 tablespoon per liter of water). Stir thoroughly. Secure the lids. Let the solution sit overnight. (The
solution will start milky white; after sitting, it should appear clear, with
precipitate at the bottom. Precipitate is a solid formed in a solution during a
chemical reaction.) Pour the clear liquid through filter
paper into the clean jars, (If you don't use filter paper, avoid
transferring any of the precipitate.) Secure
the lids on the new jars, which now contain saturated solutions of limewater.
Have
students demonstrate that their breath includes carbon dioxide. Pour a small amount
of limewater into glasses, and have students blow GENTLY through straws into
the limewater (being very careful not drink any of the liquid). As students
blow into the limewater, it will gradually change from clear to milky white.
Below is a simplified version of the reaction equation:
limewater + carbon dioxide → limestone + water
The way to
express this chemically is:
calcium hydroxide + carbon dioxide → calcium carbonate + water
The way to
express this using chemical symbols is:
Ca(OH)2 + CO2 → CaCO3 + H20
The lime in the water combines
with the CO2 in the students' breath to form limestone (i.e.
calcium carbonate) a white powder (precipitate) suspended in the liquid. (As when you prepared the limewater, if
these glasses of milky solution are left to sit, the limestone will settle to
the bottom.) To show that it is the carbon dioxide in their breath and not some
other gas that's reacting to the limewater, consider repeating the
experiment using another source of carbon dioxide, such as dry ice, seltzer, or
baking powder and vinegar.
Extension 1: Use your limewater to take carbon dioxide out of the air. Fill a
glass with limewater, let it sit somewhere safe and exposed to the air for
about a week, and pour off the remaining liquid., The white material remaining
in the glass is limestone.
Extension 2: Use vinegar to separate the lime and carbon dioxide again. Add vinegar
to a glass containing limestone and observe what happens.
Bubbles of carbon dioxide form, and gradually, the limestone exposed to the
vinegar disappears. Any limestone not in contact with the vinegar, such as high
up on the glass's sides, will remain.
Extension 3: Test rocks for the presence of limestone. Gather a
collection of rocks, including sedimentary rocks, marble (if possible), and
chalk. Pour vinegar on them and observe what happens. Rocks that contain
limestone will bubble, as carbon dioxide is released.
Web Sites
NOVA scienceNOW
www.pbs.org/wgbh/nova/sciencenow/0302/03.html
Offers resources and information related to capturing
carbon.
U.S. Department of Energy: Carbon Sequestration
fossil.energy.gov/sequestration/
Provides information and news on various carbon
sequestration research, projects, and plans.
EPA: Climate Change
www.epa.gov/climatechange/
Offers links to information on the science, effects,
policies, and economics of global climate change, as well as recommendations on
what people can do.
NASA Earth Observatory: Carbon Cycle
earthobservatory.nasa.gov/Library/CarbonCycle/carbon_cycle.html
Offers a sequence of information on the carbon cycle.
NOVA: Warnings from the Ice
www.pbs.org/wgbh/nova/warnings/
Companion to another NOVA program, which addresses the
changes taking place in the coastal ice on the Antarctic Peninsula.
Books
The Change in the Weather: People, Weather, and the
Science of Climate
by William K. Stevens.
Delta, 1999.
Discusses the science of climatic change.
New Approaches on Energy and the Environment: Policy
Advice for the President
by Richard D.
Morgenstern and Paul Portney, Editors.
RFF Press, 2004.
Contains "memos" to the United States President
(written before the 2004 election) on a variety of important policy-related
topics, including energy and climate.
They All Laughed... From Light Bulbs to Lasers: The
Fascinating Stories Behind the Great Inventions That Have Changed Our Lives
by Ira Flatow. New York:
HarperCollins, 1992.
Provides an entertaining look at various scientific
discoveries and inventions.
The Weather Makers: How Man Is Changing the Climate and
What It Means for Life on Earth
by Tim
Flannery.
Atlantic Monthly Press, 2006.
Describes global warming and its implications.
Activity Author
Teon
Edwards is a curriculum developer with a background in astrophysics,
mathematics, and the use of technology and multimedia in teaching and learning.
Since 1996, she has developed numerous science and mathematics education
materials for school, home, and informal learning environments.
References
"Undeniable Global Warming" by Naomi Oreskes. Washington Post: Sunday, December
26, 2004; Page B07.
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