© Division of Chemical Education  • www.JCE.DivCHED.org  •  Vol. 86 No. 2 February 2009  •  Journal of Chemical Education 209

In the Laboratory

Several articles in this Journal and other sources have de-scribed the use of sugar-filled and diet sodas to teach students about the concept of density, both inside aluminum soda cans (1–4) and as the liquids (5–7). This experiment is unique in that it addresses the concept of floating and sinking from a physics perspective (including concepts such as Archimedes’ principle and the principle of flotation) that are not normally discussed in chemistry classrooms. As a result, we recommend this experi-ment for students enrolled in high school or college-level physical science courses or even high-school physics courses. One author (M.J.S.) used this laboratory experiment in a two-hour college physical science course, but it could also be broken into two one-hour portions and used in a high school physical science course.

Experimental Procedures and Results

Data Collection For each soda can, students should measure the mass of the

full can. Then they slowly lower the soda can into the volume displacement container that is already filled with water. The stu-dents should collect the water being displaced from the volume displacement container into the beaker, noting whether the soda can is floating or has sunk to the bottom of the displacement container. Finally, the student should measure the mass of the water displaced by the can using the balance and the volume of the water displaced using the graduated cylinder. The data for 28 soda cans collected at 21 °C are shown in Table 1. Note that the data include three different soda cans each for Coca Cola, Diet Coca Cola, Diet Dr. Pepper, and Dr. Pepper. A previous classroom activity in this Journal (3) implied that all diet sodas

Using Soda Cans To Teach Physical Science Students about DensityMichael J. Sanger* and Teari C. HumphreysDepartment of Chemistry, Middle Tennessee State University, Murfreesboro, TN 37132; *mjsanger@mtsu.edu

Mark M. LaPorte†

Department of Physics and Astronomy, Middle Tennessee State University, Murfreesboro, TN 37132

Table 1. Mass, Volume, and Flotation Data for the Soda Cans

Soda Can Water Displacement Volume/mL

Water Displacement Mass/g

Soda Can Mass/g

Flotation Results

Density/ (g mL–1)

Big K citrus drop 384 383.47 391.94 sank 1.023Big K orange 382 381.67 394.21 sank 1.029Canada Dry ginger ale 384 383.85 383.30 floated 1.000Caffeine-free diet coke 371 370.20 369.72 floated 0.965Coca Cola zero 362 361.65 361.45 floated 0.943Coca Cola A 384 383.73 383.90 sank 1.002Coca Cola B 384 383.68 383.44 floated 1.001Coca Cola C 383 382.70 386.87 sank 1.010Diet caffeine-free Dr. Pepper 374 373.56 373.13 floated 0.974Diet caffeine-free Pepsi 372 372.18 371.26 floated 0.969Diet cherry vanilla Dr. Pepper 371 370.91 370.31 floated 0.966Diet Coca Cola A 369 368.12 367.78 floated 0.960Diet Coca Cola B 375 374.90 373.83 floated 0.976Diet Coca Cola C 368 368.29 367.57 floated 0.959Diet Dr. Pepper A 368 368.09 367.92 floated 0.960Diet Dr. Pepper B 370 369.33 368.89 floated 0.963Diet Dr. Pepper C 371 371.05 370.40 floated 0.967Diet Mountain Dew 372 370.64 370.56 floated 0.967Diet Pepsi 371 369.52 369.51 floated 0.964Dr. Pepper A 384 382.96 386.13 sank 1.008Dr. Pepper B 383 381.68 384.52 sank 1.003Dr. Pepper C 383 382.76 389.69 sank 1.017Mountain Dew 383 382.48 387.54 sank 1.011Pepsi 383 381.80 386.00 sank 1.007Pepsi one 369 368.24 367.82 floated 0.960Sprite 384 383.84 384.06 sank 1.002Sun drop 382 381.87 389.04 sank 1.015Sunkist 383 381.54 388.46 sank 1.014Note: Data collected at 21 °C.

†Current address: Department of Science, Mathematics, and Education, Motlow State Community College, Lynchberg, TN 37352.

210 Journal of Chemical Education  •  Vol. 86 No. 2 February 2009  • www.JCE.DivCHED.org  • © Division of Chemical Education

In the Laboratory

will float in water and that all sugar-filled drinks will sink in water; however, there are two sugar-filled soda cans (Canada Dry ginger ale and Coca Cola B) that floated in this experiment. This anomaly has been noted previously (4).

In this experiment, students are encouraged to work in groups of two. The instructor can decide to have each group of students collect data for all soda cans or allow each group to collect data for a few cans and pool the data for the entire class. The instructor can also decide whether each group of students will work on their own or the class will work together as a whole to analyze the data. If the instructor has access to a computer and projector, he or she may wish to project tables and graphs of data while leading the class discussion.

Comparing the Mass and Volume of Water DisplacedIn this part of the experiment, students are asked to plot

the mass of displaced water versus the volume of displaced wa-ter. The slope of this line represents the density of the displaced water, and this value can be compared to the theoretical density of water at room temperature. A plot of the mass and volume of water displaced for the 28 soda cans in Table 1 is shown in Figure 1. The slope of the line (using the formula y = mx) is 0.999 g/mL, which is very close to the theoretical density of water at 21 °C, which is 0.998 g/mL (8). Note also that the floating and sinking cans both fall on this line.

Comparing the Mass of the Soda Cans and the Mass of Water Displaced

In this part of the experiment students are asked to com-pare the mass of the soda can and the mass of water displaced by each can for the floating and sinking cans. For the floating cans, the two masses should be the same—the fact that the soda can displaces a quantity of water equal in mass to the can’s mass demonstrates Archimedes’ principle—“an immersed body is buoyed up by a force equal to the weight of the fluid it displaces” (9, p 219). For the sinking cans, the mass of the soda can should be more than the mass of water it displaces. The average mass of the water displaced by the sinking cans is 382.5 g, which corresponds to a displaced water volume of about 382.5 mL.

This volume represents the average volume of the soda cans; each of the sinking cans can exert a force (weight) greater than the weight of 383 mL of water, but once it has forced 382.5 mL of water out of the way, the soda can will sink to the bottom of the container.

The students are asked to plot the mass of each soda can versus the mass of the water displaced by the can. A plot of these data for the 28 soda cans is shown in Figure 2. In this plot, the floating soda cans form a diagonal line and the sinking cans form a vertical band. The slope of the floating cans (using the formula y = mx) is 0.999. The formula can be rearranged to mcan = 0.999mdispl water or mcan = mdispl water (Archimedes’ prin-ciple). The fact that the data for the sinking cans form a broad band instead of a single thin line implies that the masses of water displaced for each soda can (and therefore, the volumes of these soda cans) are similar but not identical. These data show a range of 381.5–383.8 g for the mass of water displaced by the sinking soda cans.

Comparing the Mass of the Soda Cans and the Volume of Water Displaced

The final plot that students are asked to make is a graph of the mass of each soda can versus the volume of water displaced by the can. A plot of these data for the 28 soda cans is shown in Figure 3. In this plot, the floating soda cans form a diago-nal line and the sinking cans form a vertical band (similar to Figure 2). The slope of the line (using the formula y = mx) is 0.998 g/mL. Since the mass of the soda cans equals the mass of water displaced by the can for the floating cans (Archimedes’ principle), this slope also corresponds to the density of the liquid in which the cans are floating (water). The fact that the data from the sinking cans form a broad band instead of a thin vertical line implies that the volumes of water displaced by each soda can are similar but not identical. These data show a range of 382–384 mL for the volume of water displaced by the sinking soda cans; the average volume of displacement for the sinking cans (which can be used as an estimate for the average volume of the floating as well as the sinking soda cans) based on the data in Table 1 is 383 mL.

Figure 2. Mass of the soda cans versus the mass of displaced water for all soda cans. Slope (floating cans) = 0.999 (R = 0.999).

Mass of Displaced Water / g385360 365 370 375 380

360

365

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385

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395

Mas

s of

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a C

ans

/ g floating canssinking cans

Figure 1. Mass of displaced water versus the volume of displaced water for all soda cans. Slope = density of water = 0.999 g/mL (R = 0.997).

Volume of Displaced Water / mL

385360 365 370 375 380360

365

370

375

380

385M

ass

of D

ispl

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floating canssinking cans

© Division of Chemical Education  • www.JCE.DivCHED.org  •  Vol. 86 No. 2 February 2009  •  Journal of Chemical Education 211

In the Laboratory

Figure 3. Mass of the soda cans versus the volume of displaced water for all soda cans. Slope (floating cans) = density of water = 0.998 g/mL (R = 0.995).

Volume of Displaced Water / mL

385360 365 370 375 380360

365

370

375

380

385

390

395

Mas

s of

Sod

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/ g floating canssinking cans

Calculating the Density of the Soda Cans

Finally, students are asked to calculate the density of the soda cans using the mass of each soda can and the average vol-ume of displaced water, which is a reasonable estimate for the volume of the soda cans. The density values calculated for each of 28 soda cans in this experiment appear in Table 1. The cans of diet sodas (all of which floated in water) had a range of densi-ties from 0.943–0.976 g/mL, and the cans of sugar-filled drinks that sank in water had a range of densities from 1.002–1.029 g/mL. The two sugar-filled soda cans that floated had densities of 1.000 g/mL (Canada Dry ginger ale) and 1.001 g/mL (Coca Cola B). The density value that separates the sinking and floating cans in this experiment was 1.001 g/mL, which is very close to the density of water at 21 °C (0.998 g/mL). The fact that objects with densities less than the density of a liquid will float in that liquid while objects with densities greater than the density of a liquid will sink in that liquid represents the principle of flotation (this is the form of the definition that is used most often by chemists).

These data also explain why some soda cans containing sugar-filled drinks will actually float in water instead of sinking (4). Some of these soda cans have densities very close to the density of water; so, slight variations in the masses or volumes of these soda cans could change their densities enough to change their abilities to float. For example, if one of these cans happened to have a slightly larger volume (bigger can) or a slightly smaller mass (less soda or more gaseous carbon dioxide in the can) than normal, it could lower the density of the soda can so that its actual density is less than the density of water and the soda can would float. On the other hand, since the soda cans filled

with diet sodas are much less dense than water, slight variations in the density of these cans would be unlikely to change their abilities to float.

Hazards

This experiment poses no significant safety hazards.

Summary

This experiment uses familiar objects (soda cans and wa-ter) to introduce physical science students to density concepts including Archimedes’ principle (the mass of liquid displaced by a floating object equals the mass of the floating object) and the principle of flotation (objects more dense than a liquid will sink in that liquid and objects less dense than the liquid will float). It also allows students to determine the density of a liquid using objects that float and sink in the liquid and introduces them to the technique of volume displacement as a way to determine the volume of an object that sinks in a liquid.

Literature Cited

1. Checkai, G.; Whitsett, J. J. Chem. Educ. 1986, 63, 515. 2. Lovely, G.; Runyan, T. Floating Cans. In Teaching Physics with

Toys; Taylor, B. A. P., Poth, J., Portman, D. J., Eds.; McGraw Hill: Middletown, OH, 1995; pp 233–237.

3. Sanger, M. J. J. Chem. Educ. 2006, 83, 1632A–1632B. 4. Jacobsen, E. K.; Paulson, D. R.; Sanger, M. J. J. Chem. Educ. 2008,

85, 18–19. 5. Mitchell, T. J. Chem. Educ. 1988, 65, 1070. 6. Henderson, S. K.; Fenn, C. A.; Domijan, J. D. J. Chem. Educ.

1998, 75, 1122–1123. 7. Herrick, R. S.; Nestor, L. P.; Benedetto, D. A. J. Chem. Educ.

1999, 76, 1411–1413. 8. Kell, G. S. In Handbook of Chemistry and Physics, 62nd ed.; Weast,

R. C., Ed.; CRC Press: Boca Raton, FL, 1981; p F-5. 9. Hewitt, P. G. Conceptual Physics, 8th ed.; Addison-Wesley: Read-

ing, MA, 1998; pp 219–224.

Supporting JCE Online Materialhttp://www.jce.divched.org/Journal/Issues/2009/Feb/abs209.html

Abstract and keywords

Full text (PDF) Links to cited JCE articles

Supplement A sheet of instructions for students An answer key to the student questions Notes for the instructor