|MadSci Network: Chemistry|
Tough problem. The carbonated beverage industry uses an apparatus called a Zahm & Nagel tester to measure CO2 pressure inside a sealed container. They then compare the pressure they measure with a temperature/pressure/solubility curve for carbon dioxide to determine exactly how much CO2 is in there. This equipment is not something you will have lying around your classroom... I suppose your choices are either: try to make the equivalent of a Zahm & Nagel tester, or use a titration method. The ZN tester is essentially a pressure gauge with an angled point strong enough to pierce the bottle cap or can. You would need to make sure the seal is tight so you don't lose any CO2 to the atmosphere (which is why the gauge is mounted on the two rails). Rather clumsy and could be difficult to use. On the other hand, you should already have what you need to titrate carbonic acid, using phenolphthalein as an indicator. CO2 reacts with water to form carbonic acid so, if you titrate the soda right after you open it, you should get a fairly accurate measure of the CO2 content. This method will run into problems if you want to titrate a cola or a darkly-colored beverage so you might think about using a pH meter to identify the titration endpoint (around pH = 7). Good luck with your experiments! I kinda miss playing with soda... Kieran
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