This experiment
can be done in a standard classroom or in a science laboratory classroom. Groups
as small as 2 students can perform the experiment successfully and groups should
not be larger than 4 students if possible. The experiment can be conducted in
approximately 10 minutes including set-up and clean-up time.
Alternative Setup: More sophisticated pumps are available that have a more constant flow rate and that can be set to specific flow rate values. The set up shown is using a computer data logger. The tubing has been insulated to protect against external exchange of heat. The data logger is also measuring the concentration of salt and the ambient temperature of the water.
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Click on either image for a larger version.
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In this movie, you can see a student opening the flow valve, injecting the ice water and then closing the flow valve. At the end of the movie, you can see the results on the computer screen. This is the group's second attempt at the data. You may notice two dips in the temperature. Since a smaller volume of water is being used (the beaker), only 10 cc of ice water is being injected. The temperature probes and the injector valve are insulated to reduce the external heat exchange. Notice the blue ice-water bath. It's important to draw the injectate quickly and introduce it into the system as soon as possible, so that the temperature of the injectate (ice water) can be assumed to be 0° C. |