Developers:
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Carol a Gougas
New Hop-Solebury High School
New Hope, PA
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Alfred Breaux
Maria Romagosa
Rohm and Haas Company
Spring House, PA
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Grade
Levels:
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Grades 9 - 12
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Discipline:
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Chemistry, Physical Science
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Goals:
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- To relate basic chemical concepts to a common food
item, soda.
- To examine the influence of CO2 on the
chemistry of soda.
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Background:
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Polyethylene terephthalate (PET) is a linear polyester
used for fibers and for blow molding soft drink bottles.
High density polyethylene is a linear chainlike molecule of
carbon atoms joined by covalent bonds. HDPE is distinguished
from polymers with branches or chains from the polymer
backbone. These branches give greater volume and lower
density than the linear polymers and are called low density
polyethylene or LDPE.
This series of labs will look at some of the reasons for
selecting PET rather than HDPE for soda bottles and the role
of carbon dioxide in soda chemistry.
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Safety Concerns:
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Teachers should stress that the soda in the lab is not to
be consumed by students. This should be made clear before
any of the soda testing is done. Also safety glasses should
be worn when working with the soda in the lab, especially
for parts of the lab generating CO2 when the
equipment will be pressurized.
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Introduction:
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Begin the labs by generating CO2 by adding
baking soda to vinegar or simply dissolving an ActiBath�
carbonated bath tablet in water inside a plastic bag.
Students will be able to see that a clear gas is being
generated as the bag begins inflating. Discuss with students
the properties of CO 2 that lead to its use as a
food additive. A splint test can also be performed.
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Part 1:
Materials:
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Taste Differences (at-home lab prior to class)
2 cans of soda
- In the evening prior to the lab, students should
obtain two cans of soda of the type to be tested in class
the next day. The first should be opened and poured into
a glass. The soda should be poured back and forth between
two glasses about ten times to degas the soda. Following
degassing, students should taste the soda and record
their observations.
- The sealed can should then be opened, poured into a
glass and immediately tasted. Students should also record
these observations. This becomes the basis for discussion
in class of the first role of CO2 in soda.
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Part 2:
Materials:
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Packaging Differences
1-2L bottle of soda
quart milk containers (source of HDPE)
cap for HDPE container with eye dropper pipet inserted
through cap
1-liter soda bottles (source of PET)
cap for PET container with eye dropper pipet inserted
through cap
small piece of PET
small piece of HDPE
empty soda cans
rubber or Nalgene tubing
clay
graduated cylinder
water trough or basin
pinch clamp, rubber band, or twist tie
gas collecting bottles or container with top, of known
volume
ice water bath
1 M copper (II) chloride solution
universal indicator
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Teacher's Notes:
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- This procedure introduces students to the reasons for
choosing PET rather than HDPE for soda containers.
- In large classes or when faced with limited lab time,
the class can be divided into groups and assigned various
15 minute time intervals.
- Class data should be recorded on the board and
students directed to graph CO2 volume (y-axis)
v. time (x-axis) for both PET and HDPE samples.
- Aluminum can crush demonstration:
An alternate way of packaging soda is the use of aluminum
cans with thin plastic liners. A simple
oxidation-reduction reaction can be performed which
oxidizes the aluminum and allows the can to be easily
ripped in half.
With a file placed in the opening of an empty aluminum
can, score the plastic liner completely around the can.
Fill the can with 1.0 M copper (II) chloride solution
(see attached Material Safety Data Sheet). Allow the
solution to remain in the can for about five minutes.
Pour out the solution and rinse the can. Hold the top and
bottom of the can and tear apart. The can will easily rip
in half. This should be done by the teacher.
This can serve as an introduction for discussion about
the usefulness of aluminum in beverage cans. Discuss the
role of the plastic liner based on the ingredients in
soda. Also discuss the characteristics of aluminum that
make it a good choice for the soda industry: It is
lightweight, has good thermal conductivity, and is
non-toxic.
- 900 mL of Canada Dry Ginger Ale produced the
following volumes of CO2 : 1,225 mL at room
temperature and 1,810 mL in hot water bath. 900 mL of
Seltzer Water produced 2,300 mL of CO2 at room
temperature. Average weight of CO2 : 16 oz.
soda 3.4 grams and 2 liters 14 grams.
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Procedure Part A:
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- Obtain a sample of PET and HDPE.
- Place the samples in a beaker of water and record
your observations.
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Procedure Part B:
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- Determine a volume of 900-mL in the samples of PET
and HDPE by filling a graduated cylinder with 900-mL of
water and transferring the water into the sample of PET.
Mark volume line with indelible marker. Repeat procedure
with sample of HDPE.
- Determine volume of CO2 initially in a
900-mL sample of soda. Fill PET bottle with sample. Seal
bottle with cap that has been drilled and fitted with a
glass dropper pipet attached to approximately 80-cm of
Nalgene tubing. If the hole drilled in the cap is
properly sized, the lip on the eye dropper pipet inside
the cap will ensure that the pipet is not expelled while
under pressure. Leather gloves should be worn by the
teacher, while drilling hole in the caps. Clamp tubing
with pinch clamp.
- To insure a tight seal, mold clay around cap
assembly.
- Invert gas collecting bottle filled with water into a
filled water trough or basin. Place Nalgene tubing from
soda sample into opening of gas collecting bottle. Remove
pinch clamp and allow CO2 from soda to be
collected. Swirl soda to remove as much CO2 as
possible. The minimum amount of CO2 will be
lost when the cap with tubing is added, if the soda is
cooled before opening.
- When collection is complete, seal gas collecting
bottle and remove from trough.
- Quickly add several drops of universal indicator to
the bottle. Replace the cap. Shake the contents and
record your observations.
- Measure volume of water remaining in the bottle.
Determine volume of CO2 by subtracting water
volume from volume of gas collecting bottle. This
procedure should be repeated every time a new type of
soda is tested.
- You are now ready to determine the differences
between using PET and HDPE. Fill the first container
bottle with sample of soda to be tested. Seal bottle
according to previous directions. Repeat procedure with
second container. Allow both containers to sit for a time
interval assigned by your teacher. At the end of the time
determine volume of CO2 remaining in both
bottles using procedure #4.
- Repeat sample test as directed by your teacher.
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Procedure Part C:
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- Place a 900-mL sample of soda in the PET container.
Seal the bottle using the same method as Procedure B.
- Place the bottle assembly in an ice water bath for
one hour.
- At the end of the hour, collect the CO2
using the same method as before. Record the volume of
CO2 generated.
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Part 3:
Materials:
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Weight Differences
1-L samples of regular, diet and club soda
balance
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Procedure:
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- Obtain a 1-L bottle of soda. Weigh the soda (Coke
Classic-- 1,094.9 grams and Diet Coke-- 1,055.5 grams)
before removing the cap and record the weight.
- Loosen the cap and remove the CO2 present
by gently swirling, being careful not to spill any
liquid. Repeat as needed to remove CO2 .
Re-weigh bottle.
- Calculate percentage of CO2 present.
Repeat for different sodas.
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Part 4:
Materials:
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pH Differences
1 can of soda
beaker
pH meter
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Procedure:
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- Using a pH meter, test the acidity of a freshly
opened bottle of soda. Record results.
- Swirl the sample to degas the soda and again test
with the pH meter. Record results.
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Teacher's Note:
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We observed a pH change of 0.3 higher with Club Soda and
0.3 lower with Canada Dry Ginger Ale. No change was observed
with pH test paper.
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Part 5:
Teacher's Notes:
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Diet vs. Regular Soda
- These procedures demonstrate two techniques for
determining the differences between diet and regular
soda. The first test is a commercially available test
strip for glucose (approximate cost $7 for a package of
50 strips).
- Test #2 takes advantage of the difference in density
between diet and regular soda. An introductory
demonstration is to simply place both cans in a large
beaker of water. The diet soda will float; the regular
soda sinks. Our data revealed the following for 12 packs
of 12 oz. Coke Classic and Diet Coke: Coke Classic high
weight was 391.3 grams, low weight was 384.0 grams,
average weight was 388.5 grams, and Relative Standard
Deviation of 0.52%. Diet Coke: high weight was 374.7
grams, low weight was 367.7 grams, average weight was
373.5 grams, and Relative Standard Deviation of 0.59%.
- Precision of experimental results can be discussed
from the class weight data. Depending on the level of
sophistication you wish to employ, the data generated in
this lab will allow students to determine the mean
weight, the median weight and also the standard deviation
of the samples. The standard deviation is determined as
follows:
a. Calculate the average of the series of
measurements.
b. Determine the deviation of each measurement from
the average.
c. Square the deviations and add up their squares.
d. Divide the sum of the squares of the deviations by
(n-1), where n is the total number of measurements.
e. Take the square root of result d.
Standard deviation gives the range of spread from the
average value within which 68% of all repeated
measurements are expected to fall.
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Materials:
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12 cans of diet soda
12 cans of regular soda
unknown samples of soda
Clinistix� test strips
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Procedure Part A:
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- Obtain a sample of an unknown soda from your teacher.
- Using a Clinistix test strip, dip the end of the
strip in the sample and remove immediately.
- Tap edge of strip against side of beaker to remove
any excess.
- After about 10 seconds, determine the color of the
strip. A deep purple color indicates the presence of
sugar in the soda. A bright pink color indicates a
negative reading.
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Procedure Part B:
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- Obtain a numbered can of diet soda and a can of
regular soda.
- Weigh each can and record the weights on a table on
the board.
- One group of students will need to determine the
weight of an aluminum can. Open the can of soda, drain
the soda, rinse the can and allow to dry. Weigh the can
and record the results. This can can be treated as a
"standard can" or an additional activity would be to get
weights on 12 cans and determine the average, high, low
and Relative Standard Deviation.
- Assume a 12-oz. volume to determine density.
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Additional Activity:
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The difference in density between diet and regular soda
can also be shown by using samples of Crystal Pepsi and Diet
Pepsi. Pour a can of Crystal Pepsi into a 250 or 500 mL
graduated cylinder. Pour the sample of Diet Pepsi carefully
down the sides of the cylinder. The Diet Pepsi will remain
on top of the clear Pepsi.
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Student Data Sheet
Part 1
Taste of soda initially
Taste of soda without CO 2
What effect on the taste of soda does CO 2 have?
What ingredients would you vary to produce a sweeter
soda?
Part 2A
Results of float test:
On the basis of the float test, which plastic is better
suited for soda packaging? Why?
On the basis of the table of densities, which plastic is
best suited for soda packaging?
What should you take into account when deciding how to
package soda?
Part 2B
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PET
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HDPE
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Initial CO2 volume
CO2 volume
after 15 min.
after 30 min
after 45 min
after 1 day
after 4 days
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Which material retains more CO2 during the
test times?
On the basis of your data, which material is better
suited for soda packaging?
Why are milk and bottled water packaged differently than
soda?
What changes were observed with the universal indicator?
What does this show?
Part 2C
Volume of CO2 obtained from ice bath
What is the relationship between temperature and the
solubility of gases?
What does this test indicate is the best way to store
soda?
Part 3
Regular Diet Club
Weight of soda initially
Weight of soda after swirling
Amount of CO2 present
% of CO2 present
What differences in carbonation did you notice among the
sodas tested?
Part 4
pH initially
pH after swirling
What effect does carbonation have on the pH of soda?
Part 5A
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Regular
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Diet
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Color of Clinistix
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Part 5B
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Weight in Grams
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Sample #
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Regular
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Diet
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1
2
3
4
5
6
7
8
9
10
11
12
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Average Weight
Weight of Aluminum Can
Weight of Soda
Volume of soda
Density of soda
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Additional Activities:
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- If a titration unit is available, Canada Dry Ginger
Ale (Citric acid -- monoprotic) and Coke Classic
(phosphoric acid -- polyprotic) could be titrated to
demonstrate the single breakpoint for the Ginger Ale and
the three breakpoints for the Coke Classic. This would be
a good lead-in to a discussion of monoprotic versus
polyprotic acids and why the hydrogens are lost at three
points for the polyprotic acid. If the titration unit is
not available in your school, ask a local business to do
the titrations for you and supply the data.
- If a spectrometer is available, the sodas could be
observed using the spectrometer (clear sodas should be
used for this activity since the caramel coloring will
block light transmission). The wavelength could be
changed by adding sodium chloride to the soda.
- Soda can be left in PET bottles or cans in a warm,
sunny area to observe the loss of the CO2 from
closed containers. This loss should be observable in one
to two weeks and is a good indication why the sodas
stored outside as a display at a gas station in the
summer may be "flat" when you drink them.
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