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NOVA scienceNOW: Capturing Carbon
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Viewing Ideas
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Before Watching
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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.
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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.
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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.)
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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.
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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.
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Glass 1: Add a known base, such as baking soda or
ammonia. (Bromothymol blue is blue in basic solutions.)
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Glass 2: Add water. (Bromothymol blue is also blue in neutral solutions.)
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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.
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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.)
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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.
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Seal one of the bags with as little air inside as possible.
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Seal a second bag with as much air inside as possible.
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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;
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Seal the third plastic bag, containing as much
CO2-rich air as possible.
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Record the temperature measured by each of the thermometers.
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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.)
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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
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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:
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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.
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the economics of changing industries and infrastructure over
to a new model
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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"
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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.
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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:
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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.
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Add about 1 tablespoon of lime to each jar (or 1 tablespoon
per liter of water).
Stir thoroughly.
Secure the lids.
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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.)
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Pour the clear liquid through filter paper into the clean
jars, (If you don't use filter paper, avoid transferring any
of the precipitate.)
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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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