Time and Soda Can Contents

name         Melissa
status       educator
grade        other
location     IA

Question -   I teach at a youth shelter.  The students, the 
teacher, and I (teacher associate) were talking about density 
today.  We preformed the experiment where a can of diet soda 
floats in water and a can of regular soda sinks.  The we passed 
around the cans of soda, so students could feel the different in 
weight.  We realized that our diet soda can (which has an 
expiration date of 1998), seemed like it had much more air 
space--the liquid sloshed around more when you shook it.  The can 
has never been opened; there is no hold in it that liquid leaks 
through.  It does not seem to make sense that some for the diet 
soda could have evaporated over the years.  Does time have an 
effect on the volume of pop?  Could something have happened to 
make the can of diet soda sound like it is MUCH LESS full than 
the can of regular soda?
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   It is possible that a 1998 can of soda developed a pinhole leak. 
And you do not know that the two samples were filled exactly the 
same. Possibly there was a problem on the filling line of one or 
the other of the cans of soda that caused them to be underfilled or 
overfilled. You can do two experiments: 1. Open the cans and weigh 
the contents. That will resolve how much difference there is in the 
amount of diet soda and regular soda. Also weigh the empty cans. It 
is possible that the two cans have different thicknesses. The 
amount of aluminum in the can would have a significant effect on 
its total density.

Vince Calder
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Melissa,

I can not imagine why you would observe a much lower volume in a can 
of soda - even if it is from 1998. Moreover, the difference in mass 
(due to sugar versus aspartame) can not account for the volume 
difference since soda is sold by volume. This means the company has 
to, at least, hit a minimum volume in each can. While there is a 
measureable leakage of CO2 through effusion in the seals of plastic 
soda bottles (at the screw), the seals in aluminum cans are much 
better so CO2 effusion is much less. Water effusion (or diffusion) 
would be even less in a soda can. So I can not imagine why you 
should observe much less volume in a soda can. The only thing I can 
suggest is to compare relatively recent cans to see if you can 
observe the same difference in volume. If so, get back to us, and I 
will think on this some more.

Greg (Roberto Gregorius)
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Hi Melissa and students!

I cannot address the "sloshiness" question; that is a qualitative observation.
In other words what may be sloshy to you might not be to me.  However, I can
address the floating.  This is an experiment that we have been doing in my
classroom for many years.  You can even go to the store and get two brand
new, equally filled sounding, cans of soda and it will work.

The soda with the sugar is more dense than the can with the artificial
sweetener,  So the diet can will float and the regular will sink..  Think of
how much lighter the sweetener packets seem to be than the the packets of
sugar.  The sugar in the sweetened soda adds mass to the solution in the
can.  It has the same volume as the diet pop.  As you know volume being
equal, the more mass in the can, the higher the density.

After you have bought two new cans of soda, pour the other two out in a
measuring cup and see if the volumes are different.  If they are, it just
might have been filled a little less at the factory than the other can.
I have noticed a difference in soda volumes in sealed 2 liter bottles at the
store.  I imagine at the bottling plant they are more worried if the cans or
bottles are under-filled than if they are over-filled. The regular soda may
just be a little over.

It is another experiment any way.

Have fun,
Martha Croll
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