Soda Chemistry
and Packaging

Developers:

Carol a Gougas
New Hop-Solebury High School
New Hope, PA

Alfred Breaux
Maria Romagosa
Rohm and Haas Company
Spring House, PA

Grade
Levels:

Grades 9 - 12

Discipline:

Chemistry, Physical Science

Goals:

1. To relate basic chemical concepts to a common food item, soda.
2. To examine the influence of CO₂ on the chemistry of soda.

Background:

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.

Safety Concerns:

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.

Introduction:

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.

Part 1:

Materials:

Taste Differences (at-home lab prior to class)

2 cans of soda

1. 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.
2. 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.

Part 2:

Materials:

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

Teacher's Notes:

1. This procedure introduces students to the reasons for choosing PET rather than HDPE for soda containers.
2. In large classes or when faced with limited lab time, the class can be divided into groups and assigned various 15 minute time intervals.
3. 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.
4. 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.
5. 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.

Procedure Part A:

1. Obtain a sample of PET and HDPE.
2. Place the samples in a beaker of water and record your observations.

Procedure Part B:

1. 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.
2. 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.
3. To insure a tight seal, mold clay around cap assembly.
4. 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.
5. When collection is complete, seal gas collecting bottle and remove from trough.
6. Quickly add several drops of universal indicator to the bottle. Replace the cap. Shake the contents and record your observations.
7. 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.
8. 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.
9. Repeat sample test as directed by your teacher.

Procedure Part C:

1. Place a 900-mL sample of soda in the PET container. Seal the bottle using the same method as Procedure B.
2. Place the bottle assembly in an ice water bath for one hour.
3. At the end of the hour, collect the CO₂ using the same method as before. Record the volume of CO₂ generated.

Part 3:

Materials:

Weight Differences

1-L samples of regular, diet and club soda
balance

Procedure:

1. 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.
2. 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.
3. Calculate percentage of CO₂ present. Repeat for different sodas.

Part 4:

Materials:

pH Differences

1 can of soda
beaker
pH meter

Procedure:

1. Using a pH meter, test the acidity of a freshly opened bottle of soda. Record results.
2. Swirl the sample to degas the soda and again test with the pH meter. Record results.

Teacher's Note:

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.

Part 5:

Teacher's Notes:

Diet vs. Regular Soda

1. 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).
2. 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%.
3. 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.

Materials:

12 cans of diet soda
12 cans of regular soda
unknown samples of soda
Clinistix� test strips

Procedure Part A:

1. Obtain a sample of an unknown soda from your teacher.
2. Using a Clinistix test strip, dip the end of the strip in the sample and remove immediately.
3. Tap edge of strip against side of beaker to remove any excess.
4. 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.

Procedure Part B:

1. Obtain a numbered can of diet soda and a can of regular soda.
2. Weigh each can and record the weights on a table on the board.
3. 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.
4. Assume a 12-oz. volume to determine density.

Additional Activity:

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.

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

	PET	HDPE
Initial CO2 volume CO2 volume after 15 min. after 30 min after 45 min after 1 day after 4 days

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

	Regular		Diet
Color of Clinistix

Part 5B

	Weight in Grams
Sample #	Regular		Diet
1 2 3 4 5 6 7 8 9 10 11 12

Average Weight

Weight of Aluminum Can

Weight of Soda

Volume of soda

Density of soda

Additional Activities:

1. 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.
2. 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.
3. 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.