Chemical Mystery #7: Curious Cans

floating cans

Chemical Mystery #7: Curious Cans

Q: Does an unopened can of soda pop float or sink in water?

A: It depends!

There are several factors involved in determining whether an unopened can of soda pop will float or sink: For example, what volume of gas is sealed in the headspace of the can? How much aluminum was used in making the can? How much soda is contained in the can? What is the composition of the beverage in the can? It is interesting that given all of these factors, almost all unopened cans of soda pop have densities very close to that of water: some a little bit higher, and others a little bit lower.1 Of course unopened cans with densities higher than water will sink, while unopened cans with densities lower than water will float.

Several people are familiar with the classic experiment in which unopened cans of regular and diet soda pop are placed in water. When doing this experiment it is observed that diet sodas tend to float, whereas sugared sodas tend to sink. These observations can be explained on the basis of the amount of material dissolved in each type of soda. The addition of solute material to water tends to increase the density of the resulting solution. Inspection of the nutritional information on any sugared soda shows that these sodas tend to contain around 10% sugar by mass. On the other hand, only miniscule amounts of sweetener are added to diet sodas (less than 0.1% by mass)2. Thus sugared sodas have higher densities than water and tend to sink while diet sodas have densities lower than water and tend to float. These observations are consistent with a paper which reported experimentally measured densities of unopened cans of soda:1 regular sodas had densities higher and diet sodas had densities lower than 1.0 g mL-1.  

While performing this classic experiment recently, I noticed some unexpected behavior. I won’t give away all the details just yet, because I’d like to share this unexpected result with you in Chemical Mystery #7: Curious Cans. Check out the video below, and see if you can solve the mystery of the curious cans! Be sure to share in the comments if you think you know what is going on.

The solution to this mystery can be found .

References:

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Concepts: 

Safety

General Safety

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For Demonstrations: Please refer to the ACS Division of Chemical Education .

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