CANCRUSH
a PLAYCHEM Experiment

Charles' Law
V1/T1 = V2/T2
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There is a Video (12.5 MB) at
http://genchem.rutgers.edu/CanCrush.wmv

Charles' Law:

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At constant PRESSURE, the Volume of a given amount of ideal gas is directly proportional to the absolute temperature.
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     Both of the above cans are being heated on the hot plate. One can has a small amount of boiling water in it, the other is dry. Both cans must remain on the hot plate for about 3-5 minutes after vigorous boiling starts in the one can. Why?
In any case bring along something to read or someone to talk to while you wait for the fun to begin.
     Using crucible tongs, first the
dry can is placed mouth down into the adjacent basin of water. Upon cooling to water temperature and while still upside down in the water basin, its opening is "tightly" covered by a large rubber stopper. The can and contained water is lifted out and set down upright. Make sure no water sucked in during the cooling is lost during this process. Also you will need the water temperature.
     Then in the same way, the
boiling water can is placed mouth down in the room temperature water basin. A second can with boiling water can be placed mouth down in an ice bath. Its reaction can be compared with that of the first.
     Using Charles' Law, the three weights, the density of water and a little logic, the average temperature while still on the hotplate of the hot gas in the dry can can be calculated to a reasonable approximation.  For this calculation, assume the atmospheric pressure remains constant and ignore the vapor pressure of water. Also the density of water can be rounded to 1.00 g/cc.

    Charles' Law is part of the Ideal Gas Law........PV=nRT
where pressure (P), the number of moles of gas (n) as well as the gas constant (R) remain constant.  What is this "constant pressure"?

As for the can(s) with the boiling water in it.......observe and explain..
  • What is the initial temperature of the water vapor in the can with the boiling water?
  • Why does the can crush rather than fill with water?
  • What does the size of the drinking hole in the top have to do with what happens?
  • What effect does the temperature of the cooling water have on the result?

How Accurate is this Experiment?
Don't throw away your thermometers yet!

The biggest error is probably caused by ignoring the partial pressure of water vapor.   Depending on the water bath temperature, an error in pressure of up to 3-5% can be made by ignoring the partial pressure of water at room temperature.
Atmospheric Pressure approximately 760 mm Hg
Vapor Pressure Water @ 25oC = 23.76 mm Hg
Vapor Pressure Water @ 0oC = 4.46 mm Hg
A 5% error in pressure translates into a 5% error in the temperature.
This is a 5% error in the absolute temperature (K).
100oC = 373.15 K
This means at 100oC or so, the error is not 5o but almost 20o!
You can figure out for yourself if neglecting the vapor pressure of water makes the calculated temperature too high or too low.
Smaller errors usually occur due to some cooling while the can is being   transferred from the hot plate to the water bath. This error can be big if you hesitate too long.
A very small error is due to not leveling the liquid levels in the  can and bath.
Density of water at 25oC is about 0.996 g/cc, rather than 1.00 g/cc

Measuring the temperature of the air in cans heated in an oven set at 127oC  gave temperatures of 120-125oC when measured by this method using P1V1/T1 = P2V2/T2.
Atmospheric pressure was corrected for the vapor pressure of water and the correct density of water was used.
 

To view some crushed cans, please click on................................. CANS

When you are finished, remember to.....................RECYCLE the ALUMINUM CANS.

R.W. Kluiber  1/13/2000; 3/15/2009