VANDERBILT STUDENT VOLUNTEERS FOR SCIENCE
http://studentorgs.vanderbilt.edu/vsvs
Effect of Carbon Dioxide on the
Environment
Spring 2013
Goal: To investigate how bubbling CO2 through water changes its acidity.
Tn State standards: GLE 0507.2.3 Establish the connections between human activities and
natural disasters and their impact on the environment.
GLE 0707.7.6 Evaluate how human activities affect the earth’s land,
oceans and atmosphere.
GLE 0807.9.3: Interpret data from an investigation to differentiate between
physical and chemical changes
LESSON OUTLINE
I. Introduction
Ask students what they know about carbon dioxide.
II. Demonstration
Demonstrate the pH’s of “rainwater”, drinking water and “ocean water” by adding
bromothymol blue to a sample of each.
III. Experiment: Bubbling Dry Ice Through “Ocean Water”.
A. Students bubble dry ice through “ocean water” and watch the color of bromothymol blue
change as it becomes more acidic.
B. Discuss how carbon dioxide is removed from air. Emphasize that rainwater, is slightly
acidic, but is NOT acid rain.
IV. Discussion on Carbon Dioxide in Oceans
Increased CO2 in the atmosphere pushes more CO2 into ocean water which makes the ocean
more acidic. This has a number of effects on plants and animals, especially calcareous ones
(animals with carbonate shells). Carbonates react with acid and dissolve, posing a threat to
animal life.
V. Effects of CO2 on Land
Carbon dioxide also affects land, especially areas rich in calcite, the same mineral in marine
animal shells. Calcite is the prime mineral in limestone, so areas with lots of limestone react
with acidified rain and dissolve. This process forms caves.
VI. Experiment – Lime Water
Students will observe the change in saturated lime water from dry ice bubbling. The solution
becomes cloudy as insoluble CaCO3 forms and then becomes clear as soluble calcium
bicarbonate forms. This precipitate and dissolution transports calcium carbonate around a
cave system, leaving caverns in some places and stalactites/stalagmites in others.
Materials:
16
plates
32
clear 6oz cups
1
plastic bag containing:
3 dropper bottles of bromothymol blue indicator
16 laminated charts
3 16 oz cups
3
250 mL bottles labeled “ocean” water (.01M NaOH)
1
100 mL bottle labeled “rain” water (.01M HCl)
1
100 mL bottle labeled drinking (tap) water
3
1
1
1
4
1
1
16
250 mL bottles containing limewater (saturated calcium hydroxide, Ca(OH) 2)
16 oz Styrofoam cup with dry ice pieces (need about 20) pieces
roll of paper towels (for spills)
trash bag (for all cups)
pairs of gloves
funnel (for cleanup)
large bottle for waste liquids
Cave formation drawings (in page protectors)
I. Introduction
Write these terms on the board: carbon dioxide, CO2, carbon dioxide sink, acidification
 Ask the students what they know about carbon dioxide. Bring up these points if the students
do not:
o Carbon dioxide is a greenhouse gas in the atmosphere but also exists in oceans.
o Air contains a very small amount of carbon dioxide (about 0.03%), while oceans contain
50 times more.
o People exhale carbon dioxide when they breathe.
o Since the Industrial Age, people have contributed additional carbon dioxide to the
atmosphere by burning fossil fuels like coal, oil, and natural gas.
o The amount of carbon dioxide in the oceans has also increased since the Industrial Age.
Explain to students that in today’s experiment they will be studying what happens when carbon
dioxide is bubbled into water. Then, after doing activities with carbon dioxide, talk with them
about the effect carbon dioxide has on ocean water.
II. Demonstration
Discussion of Acids and Bases and Indicators
 Give examples of some common acids and bases:
o Some common acids are vinegar, carbonated drinks, lemon juice.
o Some common bases are milk, tums, and soaps.
 Scientists can use indicators to test if something is acidic, basic, or neutral. Tell the students
that we are going to use an indicator called bromothymol blue for our tests.
 Using the 16 oz cups, pour “rain water” into the first cup so that it is 1/3 full.
o Pour drinking water into the second cup so that it is 1/3 full.
o Pour the “ocean water” into the third cup so that it is 1/3 full.
 Hold the cups up so that the students can see them. Have them describe the solutions.
o All the liquids are clear, and all look the same.
o Tell the students that one liquid represents ocean water, one is pure water, and
one represents rain water.
Your Notes:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
Tell the students that the 3 liquids are slightly different – one is slightly basic,
one is neutral and one is slightly acidic.
Hand out the 8 Bromothymol blue color charts (pairs will share) and tell the students to
look at them.
o
Color of bromothymol blue indicator
Blue
Green
Yellow

Acid or base?
base
neutral
acid
Add a squirt of the indicator to the each of the waters (until you get a good color in each one)
and show the students the color changes. Refer to the chart to show the different colors of the
acid, neutral and basic waters.
III. Experiment
VSVS members need to put on a pair of gloves when distributing pieces of dry ice to the
students


Tell students that today's activity involves some reactions of carbon dioxide in water.
Explain that:
o Dry ice is the solid form of carbon dioxide.
o It changes (sublimes) to CO2 gas at room temperature
o When added to water, it rapidly changes to the gas form. Some of this gas
becomes dissolved in the water.
Since dry ice is at -78 oC, tell the students not to handle or touch the dry ice.
A. Effect of bubbling carbon dioxide into “ocean” water
 Give each group a plate and each pair a 6 oz cup 1/3 filled with “ocean water” by a
VSVS member.
o Tell students to describe the liquid. It is clear.
o Tell the students this is not real ocean water but pure water with chemicals added
to it to make it similar to ocean water.

VSVS members should add a squirt of bromothymol blue indicator to each pair’s cup, so
that the color is deep blue.
Tell the students to look at the chart and make sure they know that this water is
slightly basic.
o Tell the students that dry ice (carbon dioxide) will be added to this water, and
they need to watch for any changes and record observations.
 One VSVS member should now put a piece of dry ice into each cup of the water/indicator
mixture.
Your Notes:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
o
o
Students should observe a color change as the carbon dioxide causes the
“ocean” water to change from a basic solution to neutral to acidic.
Note: Students will also observe bubbling, CO2 “fog” and condensation on the
cup. These observations are not part of the discussion in this lesson, but are an
integral part of the “Properties of CO2” lesson, taught in 5th grade, 2nd semester.
For VSVS member information only:
CO2
+
H2O
→
Carbon dioxide
water
H2CO3
carbonic acid
Explanation of Observations
When dry ice is added to water, the warmer temperature of the water causes the dry ice to
produce carbon dioxide gas bubbles, some of which dissolves in the water. When carbon dioxide
dissolves in water it forms carbonic acid, a weak acid that acidifies the solution.


Ask the students: why is rainwater more acidic than drinking water? Carbon dioxide in the
atmosphere naturally dissolves in the rain water and makes it more acidic. Remind the
students that carbonated drinks are also more acidic than drinking water.
Ask students why the ocean water is more basic than drinking water? Ocean water contains
dissolved minerals that make it basic. Remind the students that some of the same minerals
found in Tums are also found in the ocean.
B. How is carbon dioxide removed from the air?
1. By photosynthesis in plants.
2. Removal also occurs when carbon dioxide dissolves in water. Rainwater naturally
dissolves CO2. The dissolved CO2 then reacts with water to form carbonic acid, making
the rainwater naturally slightly acidic.
Emphasize that this is NOT acid rain. Acid rain is much more acidic than normal rain, and
is caused by acids formed when polluting gases NO2, SO2 and SO3 react with water.
3. More importantly, water in the oceans can also remove CO2 directly from the air.
Since most students will not understand the term “pH”, the terms “acid, base and neutral”
should be used.
For VSVS information only:
 Pure water has a pH of 7.
 Normal rainwater is slightly acidic, with a pH between 7 and 5.6 (because of the
presence of dissolved carbon dioxide).
 Acid rain is much more acidic, having a pH below 5.6.
Your Notes:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
The oceans contain 50 times more CO2 than the atmosphere.
 Oceans are called sinks for CO2. Most of the CO2 in the oceans becomes carbonic
acid.
 These natural mechanisms can remove 10 billion tons of CO2 per year.
 But burning fossil fuels puts about 25 billion tons into the air annually, so there is a
net increase of 15 billion tons per year.
IV. Discussion on the Effect of Carbon Dioxide on Oceans.
Ask students if they can think of consequences of dissolving increasing amounts of carbon
dioxide in ocean waters. It will make the oceans more acidic.
o
Acidification of the oceans has been occurring since the Industrial Revolution, over
the same time span that an increase in CO2 gas in the atmosphere has been noted.
o
The change in acidity so far is small, but greater changes are expected.
o
Acidification could adversely affect marine life, but scientists are not sure how great
the effect will be.
For VSVS information only. Calcium carbonate reacts with carbonic acid (carbon dioxide in
water) to form soluble calcium bicarbonate. Corals and shells are composed of calcium
carbonates.
The equation for this step is:
CaCO3(s) + CO2(g) + H2O → Ca(HCO3)2 (aq)
V. Effects of CO2 on Land
Tell students that CO2 in water also affects the land.
Ask them if they know of any examples of CO2 affecting land. Answers may include:
Acidic rain (but stress that normal rain is not strongly acidic), weathering of rocks. If
students don’t mention dissolving rocks, tell them that rainwater can dissolve certain
types of rock.
Tell students that rainwater seeps down through soils where CO2 levels can be 10 to 100 times
that of the atmosphere. This is because certain bacteria decompose organic material which
releases CO2 in the process. Since soil is not as open as the atmosphere, much of this CO2 gets
stuck, causing water trickling down to become much more acidic than the rainwater.
Tell students that there is a rock called limestone that contains the mineral calcite. Ask them if
they know where this rock can be found. Answer: It is common anywhere that used to be shallow
ocean. Middle Tennessee has lots of limestone because it used to be a shallow ocean.
Tell students that because calcite contains calcium, the compound calcium hydroxide is common
in the water in these areas.
Your Notes:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
VI. Experiment – Lime Water
Materials:
6 oz clear cups, 1/3rd filled with limewater (saturated calcium hydroxide, Ca(OH) 2)
20 pieces of dry ice




Give each group a 6 oz clear cup 1/3rd filled with limewater
Then go around and place a piece of dry ice in their cup of limewater.
Tell students to observe what happens. (The solution becomes cloudy in about 10 seconds
and then clears up in about 3 minutes.)
(Give groups another piece of dry ice if theirs is used before the solution turns clear.)
Equations below are for VSVS information only. Students should understand the
concept of carbonate (a base) plus an acid.
Explanation of Observations
 They should observe the solution turning cloudy, and then clearing up as more carbon
dioxide dissolves. The cloudiness is caused by the combination of carbon dioxide and
calcium hydroxide to give insoluble calcium carbonate (limestone is calcium carbonate).
Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (1)
(1)
 Adding excess CO2 (by adding more dry ice) causes the excess CO2 to react with
insoluble calcium carbonate forming calcium bicarbonate, which is soluble and clear.
CaCO3 (s) + CO2 (g) + H2O (l) → Ca(HCO3)2 (aq)
(2)
Since there are small amounts of calcium carbonate in the solution compared to the excess
CO2, eventually all the calcium carbonate will react, and the solution will become clear.
Real world application
Tell students that what they have observed illustrates the process of how a cave is formed.
Explain cave formation by asking the students to look at the drawing on their observation
sheets and explaining what happens without using chemical equations (unless students have
studied chemical equations).

Explain that the process of cave formation is very slow, taking many thousands of years
depending on the size of the cave. Cave formation occurs as follows:
o Rain dissolves some CO2 from the air as it falls.
o The rain water collects even more CO2 as it percolates through soil (because of the
concentrated amounts in the soil).
o When the rain water hits limestone, the acidified water begins to dissolve the rock.
Ask students: Why? (If you explained it clearly they should respond that the
Your Notes:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
carbonic acid in rain water reacts with calcium carbonate to form calcium
bicarbonate, which is non-solid).
o As the limestone dissolves, the aqueous calcium bicarbonate is carried away by
underground rivers. The contour of a cave is left behind.
o Many times, caves have stalagmites and stalactites, which form on the floor and
ceiling of the cave respectively. This occurs when water containing the dissolved
calcium bicarbonate evaporates, causing calcium carbonate to precipitate (reverse
of equation 2). (For VSVS’ers: this is LeChatelier’s Principle at play).
Cleanup: All the cups can be emptied into a sink and washed down with water. If there is no
sink, empty the clear cups into the waste container using the funnel, and return it with the kit.
Put all used cups in the trash bag, and return with the kit. This is important to avoid getting
the kit box wet. We reuse all cups and plates.
Note about solutions used for “simulated” ocean water and “simulated” rain water
1. We are using a pH 10 solution (NaOH) for the “simulated” ocean water to lengthen the
time needed for color changes for Bromothymol Blue indicator. This allows students
time to observe the color change from blue (basic) to green (neutral) to yellow (acidic)
when a piece of dry ice is added to the solution. The average pH of ocean water is 8.1.
When a solution with this pH is used in this activity, the addition of a piece of dry ice
causes the Bromothymol Blue color changes to occur so fast that the green color for a
neutral solution can’t be seen.
2. A pH 2 solution (0.01M HCl) is used for “simulated” rain water in the
demonstration of color changes for Bromothymol Blue to provide an intense yellow color
that can be seen by the whole class. Normal rain water slightly acidic with a pH between
5.6 and 7.
References: The World of Chemistry Essentials, 4th edition, Joesten, Castellion & Hogg
Wikipedia “Ocean Acidification”
Lesson written by: Dr. Melvin Joesten, Chemistry Department, Vanderbilt University
Pat Tellinghuisen, Program Director, VSVS, Vanderbilt University
Your Notes:
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________